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1.  Lung Cancer Occurrence in Never-Smokers: An Analysis of 13 Cohorts and 22 Cancer Registry Studies  
PLoS Medicine  2008;5(9):e185.
Background
Better information on lung cancer occurrence in lifelong nonsmokers is needed to understand gender and racial disparities and to examine how factors other than active smoking influence risk in different time periods and geographic regions.
Methods and Findings
We pooled information on lung cancer incidence and/or death rates among self-reported never-smokers from 13 large cohort studies, representing over 630,000 and 1.8 million persons for incidence and mortality, respectively. We also abstracted population-based data for women from 22 cancer registries and ten countries in time periods and geographic regions where few women smoked. Our main findings were: (1) Men had higher death rates from lung cancer than women in all age and racial groups studied; (2) male and female incidence rates were similar when standardized across all ages 40+ y, albeit with some variation by age; (3) African Americans and Asians living in Korea and Japan (but not in the US) had higher death rates from lung cancer than individuals of European descent; (4) no temporal trends were seen when comparing incidence and death rates among US women age 40–69 y during the 1930s to contemporary populations where few women smoke, or in temporal comparisons of never-smokers in two large American Cancer Society cohorts from 1959 to 2004; and (5) lung cancer incidence rates were higher and more variable among women in East Asia than in other geographic areas with low female smoking.
Conclusions
These comprehensive analyses support claims that the death rate from lung cancer among never-smokers is higher in men than in women, and in African Americans and Asians residing in Asia than in individuals of European descent, but contradict assertions that risk is increasing or that women have a higher incidence rate than men. Further research is needed on the high and variable lung cancer rates among women in Pacific Rim countries.
Michael Thun and colleagues pooled and analyzed comprehensive data on lung cancer incidence and death rates among never-smokers to examine what factors other than active smoking affect lung cancer risk.
Editors' Summary
Background.
Every year, more than 1.4 million people die from lung cancer, a leading cause of cancer deaths worldwide. In the US alone, more than 161,000 people will die from lung cancer this year. Like all cancers, lung cancer occurs when cells begin to divide uncontrollably because of changes in their genes. The main trigger for these changes in lung cancer is exposure to the chemicals in cigarette smoke—either directly through smoking cigarettes or indirectly through exposure to secondhand smoke. Eighty-five to 90% of lung cancer deaths are caused by exposure to cigarette smoke and, on average, current smokers are 15 times more likely to die from lung cancer than lifelong nonsmokers (never smokers). Furthermore, a person's cumulative lifetime risk of developing lung cancer is related to how much they smoke, to how many years they are a smoker, and—if they give up smoking—to the age at which they stop smoking.
Why Was This Study Done?
Because lung cancer is so common, even the small fraction of lung cancer that occurs in lifelong nonsmokers represents a large number of people. For example, about 20,000 of this year's US lung cancer deaths will be in never-smokers. However, very little is known about how age, sex, or race affects the incidence (the annual number of new cases of diseases in a population) or death rates from lung cancer among never-smokers. A better understanding of the patterns of lung cancer incidence and death rates among never-smokers could provide useful information about the factors other than cigarette smoke that increase the likelihood of not only never-smokers, but also former smokers and current smokers developing lung cancer. In this study, therefore, the researchers pooled and analyzed a large amount of information about lung cancer incidence and death rates among never smokers to examine what factors other than active smoking affect lung cancer risk.
What Did the Researchers Do and Find?
The researchers analyzed information on lung cancer incidence and/or death rates among nearly 2.5 million self-reported never smokers (men and women) from 13 large studies investigating the health of people in North America, Europe, and Asia. They also analyzed similar information for women taken from cancer registries in ten countries at times when very few women were smokers (for example, the US in the late 1930s). The researchers' detailed statistical analyses reveal, for example, that lung cancer death rates in African Americans and in Asians living in Korea and Japan (but not among Asians living in the US) are higher than those in people of the European continental ancestry group. They also show that men have higher death rates from lung cancer than women irrespective of racial group, but that women aged 40–59 years have a slightly higher incidence of lung cancer than men of a similar age. This difference disappears at older ages. Finally, an analysis of lung cancer incidence and death rates at different times during the past 70 years shows no evidence of an increase in the lung cancer burden among never smokers over time.
What Do These Findings Mean?
Although some of the findings described above have been hinted at in previous, smaller studies, these and other findings provide a much more accurate picture of lung cancer incidence and death rates among never smokers. Most importantly the underlying data used in these analyses are now freely available and should provide an excellent resource for future studies of lung cancer in never smokers.
Additional Information.
Please access these Web sites via the online version of this summary at http://dx.doi.org/10.1371/journal.pmed.0050185.
The US National Cancer Institute provides detailed information for patients and health professionals about all aspects of lung cancer and information on smoking and cancer (in English and Spanish)
Links to other US-based resources dealing with lung cancer are provided by MedlinePlus (in English and Spanish)
Cancer Research UK provides key facts about the link between lung cancer and smoking and information about all other aspects of lung cancer
doi:10.1371/journal.pmed.0050185
PMCID: PMC2531137  PMID: 18788891
2.  Evaluation of the Lung Cancer Risks at Which to Screen Ever- and Never-Smokers: Screening Rules Applied to the PLCO and NLST Cohorts 
PLoS Medicine  2014;11(12):e1001764.
Martin Tammemägi and colleagues evaluate which risk groups of individuals, including nonsmokers and high-risk individuals from 65 to 80 years of age, should be screened for lung cancer using computed tomography.
Please see later in the article for the Editors' Summary
Background
Lung cancer risks at which individuals should be screened with computed tomography (CT) for lung cancer are undecided. This study's objectives are to identify a risk threshold for selecting individuals for screening, to compare its efficiency with the U.S. Preventive Services Task Force (USPSTF) criteria for identifying screenees, and to determine whether never-smokers should be screened. Lung cancer risks are compared between smokers aged 55–64 and ≥65–80 y.
Methods and Findings
Applying the PLCOm2012 model, a model based on 6-y lung cancer incidence, we identified the risk threshold above which National Lung Screening Trial (NLST, n = 53,452) CT arm lung cancer mortality rates were consistently lower than rates in the chest X-ray (CXR) arm. We evaluated the USPSTF and PLCOm2012 risk criteria in intervention arm (CXR) smokers (n = 37,327) of the Prostate, Lung, Colorectal and Ovarian Cancer Screening Trial (PLCO). The numbers of smokers selected for screening, and the sensitivities, specificities, and positive predictive values (PPVs) for identifying lung cancers were assessed. A modified model (PLCOall2014) evaluated risks in never-smokers. At PLCOm2012 risk ≥0.0151, the 65th percentile of risk, the NLST CT arm mortality rates are consistently below the CXR arm's rates. The number needed to screen to prevent one lung cancer death in the 65th to 100th percentile risk group is 255 (95% CI 143 to 1,184), and in the 30th to <65th percentile risk group is 963 (95% CI 291 to −754); the number needed to screen could not be estimated in the <30th percentile risk group because of absence of lung cancer deaths. When applied to PLCO intervention arm smokers, compared to the USPSTF criteria, the PLCOm2012 risk ≥0.0151 threshold selected 8.8% fewer individuals for screening (p<0.001) but identified 12.4% more lung cancers (sensitivity 80.1% [95% CI 76.8%–83.0%] versus 71.2% [95% CI 67.6%–74.6%], p<0.001), had fewer false-positives (specificity 66.2% [95% CI 65.7%–66.7%] versus 62.7% [95% CI 62.2%–63.1%], p<0.001), and had higher PPV (4.2% [95% CI 3.9%–4.6%] versus 3.4% [95% CI 3.1%–3.7%], p<0.001). In total, 26% of individuals selected for screening based on USPSTF criteria had risks below the threshold PLCOm2012 risk ≥0.0151. Of PLCO former smokers with quit time >15 y, 8.5% had PLCOm2012 risk ≥0.0151. None of 65,711 PLCO never-smokers had PLCOm2012 risk ≥0.0151. Risks and lung cancers were significantly greater in PLCO smokers aged ≥65–80 y than in those aged 55–64 y. This study omitted cost-effectiveness analysis.
Conclusions
The USPSTF criteria for CT screening include some low-risk individuals and exclude some high-risk individuals. Use of the PLCOm2012 risk ≥0.0151 criterion can improve screening efficiency. Currently, never-smokers should not be screened. Smokers aged ≥65–80 y are a high-risk group who may benefit from screening.
Please see later in the article for the Editors' Summary
Editors' Summary
Background
Lung cancer is the most commonly occurring cancer in the world and the most common cause of cancer-related deaths. Like all cancers, lung cancer occurs when cells acquire genetic changes that allow them to grow uncontrollably and to move around the body (metastasize). The most common trigger for these genetic changes in lung cancer is exposure to cigarette smoke. Symptoms of lung cancer include a persistent cough and breathlessness. If lung cancer is diagnosed when it is confined to the lung (stage I), the tumor can often be removed surgically. Stage II tumors, which have spread into nearby lymph nodes, are usually treated with surgery plus chemotherapy or radiotherapy. For more advanced lung cancers that have spread throughout the chest (stage III) or the body (stage IV), surgery is rarely helpful and these tumors are treated with chemotherapy and radiotherapy alone. Overall, because most lung cancers are not detected until they are advanced, less than 17% of people diagnosed with lung cancer survive for five years.
Why Was This Study Done?
Screening for lung cancer—looking for early disease in healthy people—could save lives. In the US National Lung Screening Trial (NLST), annual screening with computed tomography (CT) reduced lung cancer mortality by 20% among smokers at high risk of developing cancer compared with screening with a chest X-ray. But what criteria should be used to decide who is screened for lung cancer? The US Preventive Services Task Force (USPSTF), for example, recommends annual CT screening of people who are 55–80 years old, have smoked 30 or more pack-years (one pack-year is defined as a pack of cigarettes per day for one year), and—if they are former smokers—quit smoking less than 15 years ago. However, some experts think lung cancer risk prediction models—statistical models that estimate risk based on numerous personal characteristics—should be used to select people for screening. Here, the researchers evaluate PLCOm2012, a lung cancer risk prediction model based on the incidence of lung cancer among smokers enrolled in the US Prostate, Lung, Colorectal and Ovarian Cancer Screening Trial (PLCO). Specifically, the researchers use NLST and PLCO screening trial data to identify a PLCOm2012 risk threshold for selecting people for screening and to compare the efficiency of the PLCOm2012 model and the USPSTF criteria for identifying “screenees.”
What Did the Researchers Do and Find?
By analyzing NLST data, the researchers calculated that at PLCOm2012 risk ≥0.0151, mortality (death) rates among NLST participants screened with CT were consistently below mortality rates among NLST participants screened with chest X-ray and that 255 people with a PLCOm2012 risk ≥0.0151 would need to be screened to prevent one lung cancer death. Next, they used data collected from smokers in the screened arm of the PLCO trial to compare the efficiency of the PLCOm2012 and USPSTF criteria for identifying screenees. They found that 8.8% fewer people had a PLCOm2012 risk ≥0.0151 than met USPSTF criteria for screening, but 12.4% more lung cancers were identified. Thus, using PLCOm2012 improved the sensitivity and specificity of the selection of individuals for lung cancer screening over using UPSTF criteria. Notably, 8.5% of PLCO former smokers with quit times of more than 15 years had PLCOm2012 risk ≥0.0151, none of the PLCO never-smokers had PLCOm2012 risk ≥0.0151, and the calculated risks and incidence of lung cancer were greater among PLCO smokers aged ≥65–80 years than among those aged 55–64 years.
What Do These Findings Mean?
Despite the absence of a cost-effectiveness analysis in this study, these findings suggest that the use of the PLCOm2012 risk ≥0.0151 threshold rather than USPSTF criteria for selecting individuals for lung cancer screening could improve screening efficiency. The findings have several other important implications. First, these findings suggest that screening may be justified in people who stopped smoking more than 15 years ago; USPSTF currently recommends that screening stop once an individual's quit time exceeds 15 years. Second, these findings do not support lung cancer screening among never-smokers. Finally, these findings suggest that smokers aged ≥65–80 years might benefit from screening, although the presence of additional illnesses and reduced life expectancy need to be considered before recommending the provision of routine lung cancer screening to this section of the population.
Additional Information
Please access these websites via the online version of this summary at http://dx.doi.org/10.1371/journal.pmed.1001764.
The US National Cancer Institute provides information about all aspects of lung cancer for patients and health-care professionals, including information on lung cancer screening (in English and Spanish)
Cancer Research UK also provides detailed information about lung cancer and about lung cancer screening
The UK National Health Service Choices website has a page on lung cancer that includes personal stories
MedlinePlus provides links to other sources of information about lung cancer (in English and Spanish)
Information about the USPSTF recommendations for lung cancer screening is available
doi:10.1371/journal.pmed.1001764
PMCID: PMC4251899  PMID: 25460915
3.  Cigarette smoking and the subsequent risk of lung carcinoma in the men and women of a large prospective cohort study 
The lancet oncology  2008;9(7):649-656.
Summary
Background
Whether women are more susceptible than men to lung cancer caused by cigarette smoking has been controversial. We aimed to determine the susceptibility of men and women to cigarette smoking by comparing lung carcinoma incidence rates by stratum of smoking use in the men and women of the National Institutes of Health–AARP cohort.
Methods
The analysis included 279,214 men and 184,623 women from eight U.S. states aged 50 to 71 years at study baseline who were mailed a questionnaire between October 13, 1995 and May 6, 1996 and were followed until December 31, 2003. We present age-standardized incidence rates and multivariate adjusted hazard ratios (HR) adjusted for potential confounders, each with 95% confidence intervals (CI).
Findings
During follow-up, lung carcinomas occurred in 4,097 men and 2,237 women. Incidence rates were 20.3 per 100,000 person-years (95% CI: 16.3–24.3) in never smoking men (99 carcinomas) and 25.3, 95% CI: 21.3–29.3 in never smoking women (152 carcinomas); for this group, the HR for lung carcinoma was 1.3 (95%CI: 1.0–1.8) for women relative to men. Smoking was associated with increased lung carcinoma risk in both men and women. The incidence rate of current smokers of >2 packs per day was 1,259.2 (95%CI: 1,035.0–1,483.3) in men and 1,308.9 (95%CI: 924.2–1,693.6) in women. Among current smokers, in a model adjusted for typical smoking dose, the HR was 0.9 (95%CI: 0.8–0.9) for women relative to men. For former smokers, in a model adjusted for years of cessation and typical smoking dose, the HR was 0.9 (95%CI: 0.9–1.0) for women relative to men. Incidence rates of adenocarcinoma, small cell, and undifferentiated tumors were similar in men and women; incidence rates of squamous tumors in men were twice that in women.
Interpretation
Our study suggests that women are not more susceptible than men to the carcinogenic effects of cigarette smoking in the lung. Future studies should confirm whether incidence rates are indeed higher in never smoking women than in never smoking men.
doi:10.1016/S1470-2045(08)70154-2
PMCID: PMC2601691  PMID: 18556244
4.  Current and Former Smoking and Risk for Venous Thromboembolism: A Systematic Review and Meta-Analysis 
PLoS Medicine  2013;10(9):e1001515.
In a meta-analysis of 32 observational studies involving 3,966,184 participants and 35,151 events, Suhua Wu and colleagues found that current, ever, and former smoking was associated with risk of venous thromboembolism.
Please see later in the article for the Editors' Summary
Background
Smoking is a well-established risk factor for atherosclerotic disease, but its role as an independent risk factor for venous thromboembolism (VTE) remains controversial. We conducted a meta-analysis to summarize all published prospective studies and case-control studies to update the risk for VTE in smokers and determine whether a dose–response relationship exists.
Methods and Findings
We performed a literature search using MEDLINE (source PubMed, January 1, 1966 to June 15, 2013) and EMBASE (January 1, 1980 to June 15, 2013) with no restrictions. Pooled effect estimates were obtained by using random-effects meta-analysis. Thirty-two observational studies involving 3,966,184 participants and 35,151 VTE events were identified. Compared with never smokers, the overall combined relative risks (RRs) for developing VTE were 1.17 (95% CI 1.09–1.25) for ever smokers, 1.23 (95% CI 1.14–1.33) for current smokers, and 1.10 (95% CI 1.03–1.17) for former smokers, respectively. The risk increased by 10.2% (95% CI 8.6%–11.8%) for every additional ten cigarettes per day smoked or by 6.1% (95% CI 3.8%–8.5%) for every additional ten pack-years. Analysis of 13 studies adjusted for body mass index (BMI) yielded a relatively higher RR (1.30; 95% CI 1.24–1.37) for current smokers. The population attributable fractions of VTE were 8.7% (95% CI 4.8%–12.3%) for ever smoking, 5.8% (95% CI 3.6%–8.2%) for current smoking, and 2.7% (95% CI 0.8%–4.5%) for former smoking. Smoking was associated with an absolute risk increase of 24.3 (95% CI 15.4–26.7) cases per 100,000 person-years.
Conclusions
Cigarette smoking is associated with a slightly increased risk for VTE. BMI appears to be a confounding factor in the risk estimates. The relationship between VTE and smoking has clinical relevance with respect to individual screening, risk factor modification, and the primary and secondary prevention of VTE.
Please see later in the article for the Editors' Summary
Editors' Summary
Background
Blood normally flows throughout the human body, supplying its organs and tissues with oxygen and nutrients. But, when an injury occurs, proteins called clotting factors make the blood gel (coagulate) at the injury site. The resultant clot (thrombus) plugs the wound and prevents blood loss. Occasionally, a thrombus forms inside an uninjured blood vessel and partly or completely blocks the blood flow. Clot formation inside one of the veins deep within the body, usually in a leg, is called deep vein thrombosis (DVT) and can cause pain, swelling, and redness in the affected limb. DVT can be treated with drugs that stop the blood clot from getting larger (anticoagulants) but, if left untreated, part of the clot can break off and travel to the lungs, where it can cause a life-threatening pulmonary embolism. DVT and pulmonary embolism are collectively known as venous thromboembolism (VTE). Risk factors for VTE include having an inherited blood clotting disorder, oral contraceptive use, prolonged inactivity (for example, during a long-haul plane flight), and having surgery. VTEs are present in about a third of all people who die in hospital and, in non-bedridden populations, about 10% of people die within 28 days of a first VTE event.
Why Was This Study Done?
Some but not all studies have reported that smoking is also a risk factor for VTE. A clear demonstration of a significant association (a relationship unlikely to have occurred by chance) between smoking and VTE might help to reduce the burden of VTE because smoking can potentially be reduced by encouraging individuals to quit smoking and through taxation policies and other measures designed to reduce tobacco consumption. In this systematic review and meta-analysis, the researchers examine the link between smoking and the risk of VTE in the general population and investigate whether heavy smokers have a higher risk of VTE than light smokers. A systematic review uses predefined criteria to identify all the research on a given topic; meta-analysis is a statistical method for combining the results of several studies.
What Did the Researchers Do and Find?
The researchers identified 32 observational studies (investigations that record a population's baseline characteristics and subsequent disease development) that provided data on smoking and VTE. Together, the studies involved nearly 4 million participants and recorded 35,151 VTE events. Compared with never smokers, ever smokers (current and former smokers combined) had a relative risk (RR) of developing VTE of 1.17. That is, ever smokers were 17% more likely to develop VTE than never smokers. For current smokers and former smokers, RRs were 1.23 and 1.10, respectively. Analysis of only studies that adjusted for body mass index (a measure of body fat and a known risk factor for conditions that affect the heart and circulation) yielded a slightly higher RR (1.30) for current smokers compared with never smokers. For ever smokers, the population attributable fraction (the proportional reduction in VTE that would accrue in the population if no one smoked) was 8.7%. Notably, the risk of VTE increased by 10.2% for every additional ten cigarettes smoked per day and by 6.1% for every additional ten pack-years. Thus, an individual who smoked one pack of cigarettes per day for 40 years had a 26.7% higher risk of developing VTE than someone who had never smoked. Finally, smoking was associated with an absolute risk increase of 24.3 cases of VTE per 100,000 person-years.
What Do These Findings Mean?
These findings indicate that cigarette smoking is associated with a statistically significant, slightly increased risk for VTE among the general population and reveal a dose-relationship between smoking and VTE risk. They cannot prove that smoking causes VTE—people who smoke may share other unknown characteristics (confounding factors) that are actually responsible for their increased risk of VTE. Indeed, these findings identify body mass index as a potential confounding factor that might affect the accuracy of estimates of the association between smoking and VTE risk. Although the risk of VTE associated with smoking is smaller than the risk associated with some well-established VTE risk factors, smoking is more common (globally, there are 1.1 billion smokers) and may act synergistically with some of these risk factors. Thus, smoking behavior should be considered when screening individuals for VTE and in the prevention of first and subsequent VTE events.
Additional Information
Please access these Web sites via the online version of this summary at http://dx.doi.org/10.1371/journal.pmed.1001515.
The US National Heart Lung and Blood Institute provides information on deep vein thrombosis (including an animation about how DVT causes pulmonary embolism), and information on pulmonary embolism
The UK National Health Service Choices website has information on deep vein thrombosis, including personal stories, and on pulmonary embolism; SmokeFree is a website provided by the UK National Health Service that offers advice on quitting smoking
The non-profit organization US National Blood Clot Alliance provides detailed information about deep vein thrombosis and pulmonary embolism for patients and professionals and includes a selection of personal stories about these conditions
The World Health Organization provides information about the dangers of tobacco (in several languages)
Smokefree.gov, from the US National Cancer Institute, offers online tools and resources to help people quit smoking
MedlinePlus has links to further information about deep vein thrombosis, pulmonary embolism, and the dangers of smoking (in English and Spanish)
doi:10.1371/journal.pmed.1001515
PMCID: PMC3775725  PMID: 24068896
5.  Burden of Total and Cause-Specific Mortality Related to Tobacco Smoking among Adults Aged ≥45 Years in Asia: A Pooled Analysis of 21 Cohorts 
PLoS Medicine  2014;11(4):e1001631.
Wei Zheng and colleagues quantify the burden of tobacco-smoking-related deaths for adults in Asia.
Please see later in the article for the Editors' Summary
Background
Tobacco smoking is a major risk factor for many diseases. We sought to quantify the burden of tobacco-smoking-related deaths in Asia, in parts of which men's smoking prevalence is among the world's highest.
Methods and Findings
We performed pooled analyses of data from 1,049,929 participants in 21 cohorts in Asia to quantify the risks of total and cause-specific mortality associated with tobacco smoking using adjusted hazard ratios and their 95% confidence intervals. We then estimated smoking-related deaths among adults aged ≥45 y in 2004 in Bangladesh, India, mainland China, Japan, Republic of Korea, Singapore, and Taiwan—accounting for ∼71% of Asia's total population. An approximately 1.44-fold (95% CI = 1.37–1.51) and 1.48-fold (1.38–1.58) elevated risk of death from any cause was found in male and female ever-smokers, respectively. In 2004, active tobacco smoking accounted for approximately 15.8% (95% CI = 14.3%–17.2%) and 3.3% (2.6%–4.0%) of deaths, respectively, in men and women aged ≥45 y in the seven countries/regions combined, with a total number of estimated deaths of ∼1,575,500 (95% CI = 1,398,000–1,744,700). Among men, approximately 11.4%, 30.5%, and 19.8% of deaths due to cardiovascular diseases, cancer, and respiratory diseases, respectively, were attributable to tobacco smoking. Corresponding proportions for East Asian women were 3.7%, 4.6%, and 1.7%, respectively. The strongest association with tobacco smoking was found for lung cancer: a 3- to 4-fold elevated risk, accounting for 60.5% and 16.7% of lung cancer deaths, respectively, in Asian men and East Asian women aged ≥45 y.
Conclusions
Tobacco smoking is associated with a substantially elevated risk of mortality, accounting for approximately 2 million deaths in adults aged ≥45 y throughout Asia in 2004. It is likely that smoking-related deaths in Asia will continue to rise over the next few decades if no effective smoking control programs are implemented.
Please see later in the article for the Editors' Summary
Editors' Summary
Background
Every year, more than 5 million smokers die from tobacco-related diseases. Tobacco smoking is a major risk factor for cardiovascular disease (conditions that affect the heart and the circulation), respiratory disease (conditions that affect breathing), lung cancer, and several other types of cancer. All told, tobacco smoking kills up to half its users. The ongoing global “epidemic” of tobacco smoking and tobacco-related diseases initially affected people living in the US and other Western countries, where the prevalence of smoking (the proportion of the population that smokes) in men began to rise in the early 1900s, peaking in the 1960s. A similar epidemic occurred in women about 40 years later. Smoking-related deaths began to increase in the second half of the 20th century, and by the 1990s, tobacco smoking accounted for a third of all deaths and about half of cancer deaths among men in the US and other Western countries. More recently, increased awareness of the risks of smoking and the introduction of various tobacco control measures has led to a steady decline in tobacco use and in smoking-related diseases in many developed countries.
Why Was This Study Done?
Unfortunately, less well-developed tobacco control programs, inadequate public awareness of smoking risks, and tobacco company marketing have recently led to sharp increases in the prevalence of smoking in many low- and middle-income countries, particularly in Asia. More than 50% of men in many Asian countries are now smokers, about twice the prevalence in many Western countries, and more women in some Asian countries are smoking than previously. More than half of the world's billion smokers now live in Asia. However, little is known about the burden of tobacco-related mortality (deaths) in this region. In this study, the researchers quantify the risk of total and cause-specific mortality associated with tobacco use among adults aged 45 years or older by undertaking a pooled statistical analysis of data collected from 21 Asian cohorts (groups) about their smoking history and health.
What Did the Researchers Do and Find?
For their study, the researchers used data from more than 1 million participants enrolled in studies undertaken in Bangladesh, India, mainland China, Japan, the Republic of Korea, Singapore, and Taiwan (which together account for 71% of Asia's total population). Smoking prevalences among male and female participants were 65.1% and 7.1%, respectively. Compared with never-smokers, ever-smokers had a higher risk of death from any cause in pooled analyses of all the cohorts (adjusted hazard ratios [HRs] of 1.44 and 1.48 for men and women, respectively; an adjusted HR indicates how often an event occurs in one group compared to another group after adjustment for other characteristics that affect an individual's risk of the event). Compared with never smoking, ever smoking was associated with a higher risk of death due to cardiovascular disease, cancer (particularly lung cancer), and respiratory disease among Asian men and among East Asian women. Moreover, the researchers estimate that, in the countries included in this study, tobacco smoking accounted for 15.8% of all deaths among men and 3.3% of deaths among women in 2004—a total of about 1.5 million deaths, which scales up to 2 million deaths for the population of the whole of Asia. Notably, in 2004, tobacco smoking accounted for 60.5% of lung-cancer deaths among Asian men and 16.7% of lung-cancer deaths among East Asian women.
What Do These Findings Mean?
These findings provide strong evidence that tobacco smoking is associated with a substantially raised risk of death among adults aged 45 years or older throughout Asia. The association between smoking and mortality risk in Asia reported here is weaker than that previously reported for Western countries, possibly because widespread tobacco smoking started several decades later in most Asian countries than in Europe and North America and the deleterious effects of smoking take some years to become evident. The researchers note that certain limitations of their analysis are likely to affect the accuracy of its findings. For example, because no data were available to estimate the impact of secondhand smoke, the estimate of deaths attributable to smoking is likely to be an underestimate. However, the finding that nearly 45% of the global deaths from active tobacco smoking occur in Asia highlights the urgent need to implement comprehensive tobacco control programs in Asia to reduce the burden of tobacco-related disease.
Additional Information
Please access these websites via the online version of this summary at http://dx.doi.org/10.1371/journal.pmed.1001631.
The World Health Organization provides information about the dangers of tobacco (in several languages) and about the WHO Framework Convention on Tobacco Control, an international instrument for tobacco control that came into force in February 2005 and requires parties to implement a set of core tobacco control provisions including legislation to ban tobacco advertising and to increase tobacco taxes; its 2013 report on the global tobacco epidemic is available
The US Centers for Disease Control and Prevention provides detailed information about all aspects of smoking and tobacco use
The UK National Health Services Choices website provides information about the health risks associated with smoking
MedlinePlus has links to further information about the dangers of smoking (in English and Spanish)
SmokeFree, a website provided by the UK National Health Service, offers advice on quitting smoking and includes personal stories from people who have stopped smoking
Smokefree.gov, from the US National Cancer Institute, offers online tools and resources to help people quit smoking
doi:10.1371/journal.pmed.1001631
PMCID: PMC3995657  PMID: 24756146
6.  Body Mass Index and Risk of Lung Cancer Among Never, Former, and Current Smokers 
Background
Although obesity has been directly linked to the development of many cancers, many epidemiological studies have found that body mass index (BMI)—a surrogate marker of obesity—is inversely associated with the risk of lung cancer. These studies are difficult to interpret because of potential confounding by cigarette smoking, a major risk factor for lung cancer that is associated with lower BMI.
Methods
We prospectively examined the association between BMI and the risk of lung cancer among 448 732 men and women aged 50–71 years who were recruited during 1995–1996 for the National Institutes of Health–AARP Diet and Health Study. BMI was calculated based on the participant’s self-reported height and weight on the baseline questionnaire. We identified 9437 incident lung carcinomas (including 415 in never smokers) during a mean follow-up of 9.7 years through 2006. Multivariable Cox proportional hazards regression models were used to estimate hazard ratios (HRs) and 95% confidence intervals (CIs) with adjustment for lung cancer risk factors, including smoking status. To address potential bias due to preexisting undiagnosed disease, we excluded potentially unhealthy participants in sensitivity analyses. All statistical tests were two-sided.
Results
The crude incidence rate of lung cancer over the study follow-up period was 233 per 100 000 person-years among men and 192 per 100 000 person-years among women. BMI was inversely associated with the risk of lung cancer among both men and women (BMI ≥35 vs 22.5–24.99 kg/m2: HR = 0.81, 95% CI = 0.70 to 0.94 and HR = 0.73, 95% CI = 0.61 to 0.87, respectively). The inverse association was restricted to current and former smokers and was stronger after adjustment for smoking. Among smokers, the inverse association persisted even after finely stratifying on smoking status, time since quitting smoking, and number of cigarettes smoked per day. Sensitivity analyses did not support the possibility that the inverse association was due to prevalent undiagnosed disease.
Conclusions
Our results suggest that a higher BMI is associated with a reduced risk of lung cancer in current and former smokers. Our inability to attribute the inverse association between BMI and the risk of lung cancer to residual confounding by smoking or to bias suggests the need for considering other explanations.
doi:10.1093/jnci/djs179
PMCID: PMC3352831  PMID: 22457475
7.  Association between smoking and risk of bladder cancer among men and women 
Context
Previous studies indicate that the population attributable risk of bladder cancer for tobacco smoking is 50–65% in men and 20–30% in women and that current cigarette smoking triples bladder cancer risk relative to never smoking. Over the last 30 years, incidence rates have remained stable in the United States (men: 123.8/100,000 person-years to 142.2/100,000 person-years; women: 32.5/100,000 person-years to 33.2/100,000 person-years), yet changing smoking prevalence and cigarette composition warrant revisiting risk estimates for smoking and bladder cancer in more recent data.
Objective
To evaluate the association between tobacco smoking and bladder cancer.
Design, Setting, and Participants
Men (n=281,394) and women (n=186,134) of the NIH-AARP cohort completed a lifestyle questionnaire and were followed from 1995 through Dec 31, 2006. Previous prospective cohort studies of smoking and incident bladder cancer were identified by systematic review and pooled using fixed effects models with heterogeneity assessed by I2.
Main outcome measures
Hazard ratios (HR), population attributable risks, and number needed to harm (NNH).
Results
During 4,518,938 years of follow-up, incident bladder cancer occurred in 3,896 men (144.0/100,000 person-years) and 627 women (34.5/100,000 person-years). Former smokers (119.8/100,000 person-years, HR: 2.22, 95%CI: 2.03–2.44, NNH: 1,250) and current smokers (177.3/100,000 person-years, HR: 4.06, 95%CI: 3.66–4.50; NNH: 727) had higher risks of bladder cancer than never smokers (39.8/100,000 person-years). In contrast, the summary risk estimate for current smoking in seven previous studies (initiated from 1963–1987) was 2.94 (95%CI: 2.45–3.54; I2=0.0%). The population attributable risk for ever smoking in our study was 0.50 (95%CI: 0.45–0.54) in men and 0.52 (95%CI: 0.45–0.59) in women.
Conclusions
Compared to a pooled estimate of US data from cohorts initiated between 1963 and 1987, relative risks for smoking in the more recent NIH-AARP cohort were higher, with population attributable risks for women comparable to those for men.
doi:10.1001/jama.2011.1142
PMCID: PMC3441175  PMID: 21846855
8.  The changing epidemiology of smoking and lung cancer histology. 
Environmental Health Perspectives  1995;103(Suppl 8):143-148.
In 1950, the first large-scale epidemiological studies demonstrated that lung cancer is causatively associated with cigarette smoking, a finding subsequently confirmed by the Royal College of Physicians in London, the U.S. Surgeon General, and the World Health Organization. Although cigarette consumption has gradually decreased in the United States from a high of about 3800 cigarettes per adult per year in 1965 to about 2800 cigarettes in 1993, death from lung cancer has reached a high among males at the rate of 74.9/100,000/year and among females at the rate of 28.5. However, in the younger cohorts, the lung cancer death rate is decreasing in both men and women. In this overview we discuss the steeper increase during recent decades of lung adenocarcinoma incidence compared with squamous cell carcinoma of the lung. In 1950, the ratio of these two major types of lung cancer in males was about 1:18; today it is about 1:1.2-1.4. This overview discusses two concepts that are regarded as contributors to this change in the histological types of lung cancer. One factor is the decrease in average nicotine and tar delivery of cigarettes from about 2.7 and 38 mg in 1955 to 1.0 and 13.5 mg in 1993, respectively. Other major factors for the reduced emission of smoke relate to changes in the composition of the cigarette tobacco blend and general acceptance of cigarettes with filter tips; the latter constitute 97% of all cigarettes currently sold. However, smokers of low-yield cigarettes compensate for the low delivery of nicotine by inhaling the smoke more deeply and by smoking more intensely; such smokers may be taking up to 5 puffs/min with puff volumes up to 55 ml. Under these conditions, the peripheral lung is exposed to increased amounts of smoke carcinogens that are suspected to lead to lung adenocarcinoma. Among the important changes in the composition of the tobacco blend of the U.S. cigarette is a significant increase in nitrate content (0.5% to 1.2-1.5%), which raises the yields of nitrogen oxides and N-nitrosamines in the smoke. Furthermore, the more intense smoking by the consumers of low-yield cigarettes increases N-nitrosamines in the smoke 2- to 3-fold. Among the N-nitrosamines is 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK), a powerful lung carcinogen in animals that is exclusively formed from nicotine. This organ-specific tobacco-specific nitrosamine (TSNA) induces adenocarcinoma of the lung. All of these factors, the more intense smoking, the deeper inhalation of the smoke, and the increased yields of N-nitrosamines in the smoke of low-yield cigarettes, are considered major contributors to the drastic increase in lung adenocarcinoma among cigarette smokers in recent years. This overview also discusses the differences in the major lung cancer types in female compared with male smokers as well as the likely underlying factors for increased lung cancer risk among African Americans compared with that among white Americans. Although the only sure way to prevent smoking-related diseases is giving up the tobacco habit, there must be a measure of protection for those who cannot accomplish this. Therefore, setting upper permissible limits of tar levels for the smoke of U.S. cigarettes, similar to strategies already taken in Western Europe, should be considered.
PMCID: PMC1518964  PMID: 8741774
9.  Risk of a Second Primary Cancer after Non-melanoma Skin Cancer in White Men and Women: A Prospective Cohort Study 
PLoS Medicine  2013;10(4):e1001433.
Studies have suggested a positive association between history of non-melanoma skin cancer (NMSC) and risk of subsequent cancer at other sites. This prospective study found a modestly increased risk of subsequent malignancies among individuals with a history of NMSC, specifically breast and lung cancer in women and melanoma in both men and women.
Background
Previous studies suggest a positive association between history of non-melanoma skin cancer (NMSC) and risk of subsequent cancer at other sites. The purpose of this study is to prospectively examine the risk of primary cancer according to personal history of NMSC.
Methods and Findings
In two large US cohorts, the Health Professionals Follow-up Study (HPFS) and the Nurses' Health Study (NHS), we prospectively investigated this association in self-identified white men and women. In the HPFS, we followed 46,237 men from June 1986 to June 2008 (833,496 person-years). In the NHS, we followed 107,339 women from June 1984 to June 2008 (2,116,178 person-years). We documented 29,447 incident cancer cases other than NMSC. Cox proportional hazard models were used to calculate relative risks (RRs) and 95% confidence intervals (CIs). A personal history of NMSC was significantly associated with a higher risk of other primary cancers excluding melanoma in men (RR = 1.11; 95% CI 1.05–1.18), and in women (RR = 1.20; 95% CI 1.15–1.25). Age-standardized absolute risk (AR) was 176 in men and 182 in women per 100,000 person-years. For individual cancer sites, after the Bonferroni correction for multiple comparisons (n = 28), in men, a personal history of NMSC was significantly associated with an increased risk of melanoma (RR = 1.99, AR = 116 per 100,000 person-years). In women, a personal history of NMSC was significantly associated with an increased risk of breast (RR = 1.19, AR = 87 per 100,000 person-years), lung (RR = 1.32, AR = 22 per 100,000 person-years), and melanoma (RR = 2.58, AR = 79 per 100,000 person-years).
Conclusion
This prospective study found a modestly increased risk of subsequent malignancies among individuals with a history of NMSC, specifically breast and lung cancer in women and melanoma in both men and women.
Please see later in the article for the Editors' Summary
Editors' Summary
Background
In the United Kingdom and the United States, about one in three people develop cancer during their lifetime and, worldwide, cancer is responsible for 13% of all deaths. Primary cancer, which can develop anywhere in the body, occurs when a cell begins to divide uncontrollably because of alterations (mutations) in its genes. Additional mutations allow the malignancy to spread around the body (metastasize) and form secondary cancers. The mutations that initiate cancer can be triggered by exposure to carcinogens such as cigarette smoke (lung cancer) or the ultraviolet (UV) radiation in sunlight (skin cancers). Other risk factors for the development of cancer include an unhealthy diet, physical inactivity, and alcohol use. In the United States, the most common cancer is non-melanoma skin cancer (NMSC). Although more than 2 million new cases of NMSC occur each year, fewer than 1,000 people die annually in the United States from the condition because the two types of NMSC—basal cell carcinoma and squamous cell carcinoma—rarely metastasize and can usually be treated by surgically removing the tumor.
Why Was This Study Done?
Some studies have suggested that people who have had NMSC have a higher risk of developing primary cancer at other sites than people who have not had NMSC. Such a situation could arise if exposure to certain carcinogens initiates both NMSC and other cancers or if NMSC shares a molecular mechanism with other cancers such as a deficiency in the DNA repair mechanisms that normally remove mutations. If people with a history of NMSC are at a greater risk of developing further cancers, a specific surveillance program for such people might help to catch subsequent cancers early when they can be successfully treated. In this prospective cohort study, the researchers examine the risk of primary cancer according to personal history of NMSC in two large US cohorts (groups)—the Health Professionals Follow-up Study (HPFS) and the Nurses' Health Study (NHS). The HPFS, which enrolled 51,529 male health professionals in 1986, and the NHS, which enrolled 121,700 female nurses in 1976, were both designed to investigate associations between nutritional factors and the incidence of serious illnesses. Study participants completed a baseline questionnaire about their lifestyle, diet and medical history. This information is updated biennially through follow-up questionnaires.
What Did the Researchers Do and Find?
The researchers identified 36,102 new cases of NMSC and 29,447 new cases of other primary cancers from 1984 in white NHS participants and from 1986 in white HPFS participants through 2008. They then used statistical models to investigate whether a personal history of NMSC was associated with a higher risk of subsequent primary cancers after accounting for other factors (confounders) that might affect cancer risk. A history of NMSC was significantly associated with an 11% higher risk of other primary cancers excluding melanoma (another type of skin cancer that, like NMSC, is linked to overexposure to UV light) in men and a 20% higher risk of other primary cancers excluding melanoma in women; a significant association is one that is unlikely to have happened by chance. The absolute risk of a primary cancer among men and women with a history of NMSC was 176 and 182 per 100,000 person-years, respectively. For individual cancer sites, after correction for multiple comparisons (when several conditions are compared in groups of people, statistically significant differences between the groups can occur by chance), a history of NMSC was significantly associated with an increased risk of breast and lung cancer in women and of melanoma in men and women.
What Do These Findings Mean?
These findings suggest that there is a modestly increased risk of subsequent malignancies among white individuals with a history of NMSC. Although the researchers adjusted for many confounding lifestyle factors, the observed association between NMSC and subsequent primary cancers may nevertheless be the result of residual confounding, so it is still difficult to be sure that there is a real biological association (due to, for example, a deficiency in DNA repair) between NMSC and subsequent primary cancers. Because of this and other study limitations, the findings reported here should be interpreted cautiously and do not suggest that individuals who have had NMSC should undergo increased cancer surveillance. These findings do, however, support the need for continued investigation of the apparent relationship between NMSC and subsequent cancers.
Additional Information
Please access these Web sites via the online version of this summary at http://dx.doi.org/10.1371/journal.pmed.1001433.
The US National Cancer Institute provides information on all aspects of cancer and has detailed information about non-melanoma skin cancer for patients and professionals (in English and Spanish)
The non-profit organization American Cancer Society provides information on cancer and how it develops and specific information on skin cancer (in several languages); its website includes personal stories about cancer
The UK National Health Service Choices website includes an introduction to cancer and a page on non-melanoma skin cancer
The non-profit organization Cancer Research UK provides basic information about cancer and detailed information on non-melanoma skin cancer
doi:10.1371/journal.pmed.1001433
PMCID: PMC3635863  PMID: 23630459
10.  Smoking and Prostate Cancer Survival and Recurrence 
Context
Studies of smoking in relation to prostate cancer mortality or recurrence in prostate cancer patients are limited, with few prostate cancer-specific outcomes.
Objective
To assess the relation of cigarette smoking and smoking cessation with overall, prostate cancer-specific, and CVD mortality and biochemical recurrence among men with prostate cancer.
Design, Setting, and Participants
Prospective observational study of 5 366 men diagnosed with prostate cancer between 1986–2006 in the Health Professionals Follow-Up Study.
Main Outcome Measures
Hazard ratios (HRs) for overall, prostate cancer-specific, and CVD mortality, and biochemical recurrence, defined by PSA rise.
Results
We documented 1,630 deaths, 524 (32%) due to prostate cancer and 416 (26%) due to CVD, and 878 biochemical recurrences. The absolute crude rates for prostate cancer-specific death for never smokers vs. current smokers were 9.6 vs. 15.3 per 1,000 person-years; for all-cause mortality the corresponding rates were 27.3 and 53.0 per 1,000 person-years. In multivariable analysis, compared with never smokers, current smokers had an increased risk of prostate cancer mortality (HR, 1.61; 95% confidence interval [CI], 1.11–2.32 and among men with clinical stage T1–T3: HR, 1.80; 95% CI, 1.04–3.12), biochemical recurrence (HR, 1.61; 95% CI, 1.16–2.22), total mortality (HR, 2.28; 95% CI, 1.87–2.80), and CVD mortality (HR, 2.13; 95% CI, 1.39–3.26). After adjusting for clinical stage and grade which are likely intermediates of the relation of smoking with prostate cancer recurrence and survival, the estimates for current smoking were as follows: prostate cancer mortality (HR, 1.38; 95% CI, 0.94–2.03 and HR, 1.41; 95% CI, 0.80–2.49); biochemical recurrence (HR, 1.47; 95% CI, 1.06–2.04). A greater number of pack-years was associated with a significantly increased risk of prostate cancer mortality but not biochemical recurrence: for current smokers of 40+ pack-years compared to never smokers: prostate cancer mortality (HR, 1.82; 95% CI, 1.03–3.20; biochemical recurrence (HR, 1.48; 95% CI, 0.88–2.48). Compared to current smokers, those who had quit smoking for 10 or more years, or who had quit for less than 10 years but smoked less than 20 pack-years, had prostate cancer mortality risks similar to never smokers: former smoker, quit 10+ years (HR, 0.60; 95% CI, 0.42–0.87); quit <10 years and <20 pack-years (HR, 0.64; 95% CI, 0.28–1.45); never smoker (HR, 0.61; 95% CI, 0.42–0.88).
Conclusions
Smoking at the time of prostate cancer diagnosis is associated with increased overall and CVD mortality and prostate cancer-specific mortality and recurrence. 10-year quitters have prostate cancer-specific mortality risks similar to never smokers.
doi:10.1001/jama.2011.879
PMCID: PMC3562349  PMID: 21693743
11.  Characterisation of smoking behaviour across the life course and its impact on decline in lung function and all-cause mortality: evidence from a British birth cohort 
Objectives:
To describe smoking trajectories from early adolescence into mid-life and to examine the effects of these trajectories on health and all-cause mortality.
Methods:
A nationally representative birth cohort study including 3387 men and women followed up since their birth in 1946 in England, Scotland and Wales. The main outcome measure is all-cause mortality by age 60 years and rate of decline in forced expiratory volume in 1 second (FEV1).
Results:
Eighteen per cent of the sample were categorised as lifelong smokers (smokers at all six waves at ages 20, 25, 31, 36, 43, 53 years), of whom 90% had begun smoking by age 18 years. By age 60 years, 10% of all lifelong smokers had died. They had a threefold increase in mortality rate compared with never smokers (hazard ratio (HR) 3.2, 95% confidence interval (CI) 2.1 to 4.8). For predominantly smokers (smokers for at least four of the six data collections), mortality rate remained higher than never smokers (HR 1.6, 95% CI 1.0 to 2.5). Predominantly non-smokers did not differ from those who never smoked (HR 1.3, 95% CI 0.9 to 2.0). Using the most recent smoking status available, current smokers had more than double the risk of mortality compared with never smokers (HR 2.4, 95% CI 1.6 to 3.5). Lifelong smokers and predominantly smokers had a greater rate of decline in lung function than never smokers (regression coefficients −18 ml/year, 95% CI −22 to −13; −6, 95% CI −10.3 to −1.7 respectively). For current smokers, the decline was 8.4 ml/year (95% CI −12.0 to −5.0) faster than never smokers.
Conclusions:
The strength and differentiation of adverse effects identified by using simplified smoking behaviours has highlighted the advantages of obtaining further information on lifelong smoking behaviour from former smokers, rather than just current smoking status.
doi:10.1136/jech.2007.068312
PMCID: PMC2774042  PMID: 18450766
12.  The 21st century hazards of smoking and benefits of stopping: a prospective study of one million women in the UK 
Lancet  2013;381(9861):133-141.
Summary
Background
Women born around 1940 in countries such as the UK and USA were the first generation in which many smoked substantial numbers of cigarettes throughout adult life. Hence, only in the 21st century can we observe directly the full effects of prolonged smoking, and of prolonged cessation, on mortality among women in the UK.
Methods
For this prospective study, 1·3 million UK women were recruited in 1996–2001 and resurveyed postally about 3 and 8 years later. All were followed to Jan 1, 2011, through national mortality records (mean 12 woman-years, SD 2). Participants were asked at entry whether they were current or ex-smokers, and how many cigarettes they currently smoked. Those who were ex-smokers at both entry and the 3-year resurvey and had stopped before the age of 55 years were categorised by the age they had stopped smoking. We used Cox regression models to obtain adjusted relative risks that compared categories of smokers or ex-smokers with otherwise similar never-smokers.
Findings
After excluding 0·1 million women with previous disease, 1·2 million women remained, with median birth year 1943 (IQR 1938–46) and age 55 years (IQR 52–60). Overall, 6% (66 489/1 180 652) died, at mean age 65 years (SD 6). At baseline, 20% (232 461) were current smokers, 28% (328 417) were ex-smokers, and 52% (619 774) were never-smokers. For 12-year mortality, those smoking at baseline had a mortality rate ratio of 2·76 (95% CI 2·71–2·81) compared with never-smokers, even though 44% (37 240/85 256) of the baseline smokers who responded to the 8-year resurvey had by then stopped smoking. Mortality was tripled, largely irrespective of age, in those still smoking at the 3-year resurvey (rate ratio 2·97, 2·88–3·07). Even for women smoking fewer than ten cigarettes per day at baseline, 12-year mortality was doubled (rate ratio 1·98, 1·91–2·04). Of the 30 most common causes of death, 23 were increased significantly in smokers; for lung cancer, the rate ratio was 21·4 (19·7–23·2). The excess mortality among smokers (in comparison with never-smokers) was mainly from diseases that, like lung cancer, can be caused by smoking. Among ex-smokers who had stopped permanently at ages 25–34 years or at ages 35–44 years, the respective relative risks were 1·05 (95% CI 1·00–1·11) and 1·20 (1·14–1·26) for all-cause mortality and 1·84 (1·45–2·34) and 3·34 (2·76–4·03) for lung cancer mortality. Thus, although some excess mortality remains among these long-term ex-smokers, it is only 3% and 10% of the excess mortality among continuing smokers. If combined with 2010 UK national death rates, tripled mortality rates among smokers indicate 53% of smokers and 22% of never-smokers dying before age 80 years, and an 11-year lifespan difference.
Interpretation
Among UK women, two-thirds of all deaths of smokers in their 50s, 60s, and 70s are caused by smoking; smokers lose at least 10 years of lifespan. Although the hazards of smoking until age 40 years and then stopping are substantial, the hazards of continuing are ten times greater. Stopping before age 40 years (and preferably well before age 40 years) avoids more than 90% of the excess mortality caused by continuing smoking; stopping before age 30 years avoids more than 97% of it.
Funding
Cancer Research UK, Medical Research Council.
doi:10.1016/S0140-6736(12)61720-6
PMCID: PMC3547248  PMID: 23107252
13.  Lung Cancer Risk Among Smokers of Menthol Cigarettes 
Background
Menthol cigarettes, preferred by African American smokers, have been conjectured to be harder to quit and to contribute to the excess lung cancer burden among black men in the Unites States. However, data showing an association between smoking menthol cigarettes and increased lung cancer risk compared with smoking nonmenthol cigarettes are limited. The Food and Drug Administration is currently considering whether to ban the sale of menthol cigarettes in the United States.
Methods
We conducted a prospective study among 85 806 racially diverse adults enrolled in the Southern Community Cohort Study during March 2002 to September 2009 according to cigarette smoking status, with smokers classified by preference for menthol vs nonmenthol cigarettes. Among 12 373 smokers who responded to a follow-up questionnaire, we compared rates of quitting between menthol and nonmenthol smokers. In a nested case–control analysis of 440 incident lung cancer case patients and 2213 matched control subjects, using logistic regression modeling we computed odds ratios (ORs) and accompanying 95% confidence intervals (CIs) of lung cancer incidence, and applied Cox proportional hazards modeling to estimate hazard ratios (HRs) of lung cancer mortality, according to menthol preference.
Results
Among both blacks and whites, menthol smokers reported smoking fewer cigarettes per day; an average of 1.6 (95% CI = 1.3 to 2.0) fewer for blacks and 1.8 (95% CI = 1.3 to 2.3) fewer for whites, compared with nonmenthol smokers. During an average of 4.3 years of follow-up, 21% of participants smoking at baseline had quit, with menthol and nonmenthol smokers having equal odds of quitting (OR = 1.02, 95% CI = 0.89 to 1.16). A lower lung cancer incidence was noted in menthol vs nonmenthol smokers (for smokers of <10, 10–19, and ≥20 cigarettes per day, compared with never smokers, OR = 5.0 vs 10.3, 8.7 vs 12.9, and 12.2 vs 21.1, respectively). These trends were mirrored for lung cancer mortality. In multivariable analyses adjusted for pack-years of smoking, menthol cigarettes were associated with a lower lung cancer incidence (OR = 0.65, 95% CI = 0.47 to 0.90) and mortality (hazard ratio of mortality = 0.69, 95% CI = 0.49 to 0.95) than nonmenthol cigarettes.
Conclusions
The findings suggest that menthol cigarettes are no more, and perhaps less, harmful than nonmenthol cigarettes.
doi:10.1093/jnci/djr102
PMCID: PMC3096798  PMID: 21436064
14.  Smoking and lung cancer: current trends in Austria 
Wiener klinische Wochenschrift  2012;124(0):493-499.
Summary
Background
Despite a recent decline in smoking behavior in many European countries, lung cancer rates remain high, especially in Central and Eastern Europe. This paper aims to describe trends in smoking behavior and lung cancer incidence and mortality, including histopathological classification of lung cancer, in a Central European country: Austria.
Methods
Using data from the Austrian Central Cancer Registry, we calculated age-standardized incidence, histopathology-specific incidence, and age-standardized and birth cohort-specific mortality rates for all lung cancer cases in Austria. Using national survey data, we estimated prevalence of smoking in the Austrian population. Our analysis covers the time period from 1970 to 2009.
Results
In 2009, lung cancer incidence rates were 41.3/100,000 and 18.5/100,000 and mortality rates were 36.3/100,000 and14.5/100,000, for males and females, respectively. Male lung cancer rates declined but increased steadily in females over the past three decades. In 2009, the most common histological type is adenocarcinoma, which reflects a shift from predominantly squamous cell carcinoma and large cell carcinoma in the mid 1980s. In 2009, 27 % of men and 19 % of women were smokers, which represent a rise of smoking rates in women, especially in younger women, and a decline in the men.
Conclusions
While in Austrian men the lung cancer rates, in accordance with their decreasing prevalence of smoking, declined over the past 30 years, the increasing smoking prevalence and lung cancer rates in women remain a public health concern. Antismoking laws and public health initiatives to curtail smoking habits are needed in Austria, especially targeting younger women.
doi:10.1007/s00508-012-0207-0
PMCID: PMC3782091  PMID: 22815002
Lung cancer; Smoking; Austria; Public health
15.  A regression model for risk difference estimation in population-based case–control studies clarifies gender differences in lung cancer risk of smokers and never smokers 
Background
Additive risk models are necessary for understanding the joint effects of exposures on individual and population disease risk. Yet technical challenges have limited the consideration of additive risk models in case–control studies.
Methods
Using a flexible risk regression model that allows additive and multiplicative components to estimate absolute risks and risk differences, we report a new analysis of data from the population-based case–control Environment And Genetics in Lung cancer Etiology study, conducted in Northern Italy between 2002–2005. The analysis provides estimates of the gender-specific absolute risk (cumulative risk) for non-smoking- and smoking-associated lung cancer, adjusted for demographic, occupational, and smoking history variables.
Results
In the multiple-variable lexpit regression, the adjusted 3-year absolute risk of lung cancer in never smokers was 4.6 per 100,000 persons higher in women than men. However, the absolute increase in 3-year risk of lung cancer for every 10 additional pack-years smoked was less for women than men, 13.6 versus 52.9 per 100,000 persons.
Conclusions
In a Northern Italian population, the absolute risk of lung cancer among never smokers is higher in women than men but among smokers is lower in women than men. Lexpit regression is a novel approach to additive-multiplicative risk modeling that can contribute to clearer interpretation of population-based case–control studies.
doi:10.1186/1471-2288-13-143
PMCID: PMC3840559  PMID: 24252624
Additive risk; Absolute risk; Case–control study; EAGLE; Lung cancer; Risk assessment; Sex factors; Smoking
16.  The risk of lung cancer with increasing time since ceasing exposure to asbestos and quitting smoking 
Objectives
To examine if the risk of lung cancer declines with increasing time since ceasing exposure to asbestos and quitting smoking, and to determine the relative asbestos effect between non‐smokers and current smokers.
Methods
A cohort study of 2935 former workers of the crocidolite mine and mill at Wittenoom, who responded to a questionnaire on smoking first issued in 1979 and on whom quantitative estimates of asbestos exposure are known. Conditional logistic regression was used to relate asbestos exposure, smoking category, and risk of lung cancer.
Results
Eighteen per cent of the cohort reported never smoking; 66% of cases and 50% of non‐cases were current smokers. Past smokers who ceased smoking within six years of the survey (OR = 22.1, 95% CI 5.6 to 87.0), those who ceased smoking 20 or more years before the survey (OR = 1.9, 95% CI 0.50 to 7.2), and current smokers (<20 cigarettes per day (OR = 6.8, 95% CI 2.0 to 22.7) or >20 cigarettes per day (OR = 13.2, 95% CI 4.1 to 42.5)) had higher risks of lung cancer compared to never smokers after adjusting for asbestos exposure and age. The asbestos effect between non‐smokers and current smokers was 1.23 (95% CI 0.35 to 4.32).
Conclusion
Persons exposed to asbestos and tobacco but who subsequently quit, remain at an increased risk for lung cancer up to 20 years after smoking cessation, compared to never smokers. Although the relative risk of lung cancer appears higher in never and ex‐smokers than in current smokers, those who both smoke and have been exposed to asbestos have the highest risk; this study emphasises the importance of smoking prevention and smoking cessation programmes within this high risk cohort.
doi:10.1136/oem.2005.025379
PMCID: PMC2078130  PMID: 16849527
smoking cessation; asbestos; lung cancer; relative asbestos effect
17.  Contribution of H. pylori and Smoking Trends to US Incidence of Intestinal-Type Noncardia Gastric Adenocarcinoma: A Microsimulation Model 
PLoS Medicine  2013;10(5):e1001451.
Jennifer Yeh and colleagues examine the contribution of IHelicobacter pyloriI and smoking trends to the incidence of past and future intestinal-type noncardia gastric adenocarcinoma.
Please see later in the article for the Editors' Summary
Background
Although gastric cancer has declined dramatically in the US, the disease remains the second leading cause of cancer mortality worldwide. A better understanding of reasons for the decline can provide important insights into effective preventive strategies. We sought to estimate the contribution of risk factor trends on past and future intestinal-type noncardia gastric adenocarcinoma (NCGA) incidence.
Methods and Findings
We developed a population-based microsimulation model of intestinal-type NCGA and calibrated it to US epidemiologic data on precancerous lesions and cancer. The model explicitly incorporated the impact of Helicobacter pylori and smoking on disease natural history, for which birth cohort-specific trends were derived from the National Health and Nutrition Examination Survey (NHANES) and National Health Interview Survey (NHIS). Between 1978 and 2008, the model estimated that intestinal-type NCGA incidence declined 60% from 11.0 to 4.4 per 100,000 men, <3% discrepancy from national statistics. H. pylori and smoking trends combined accounted for 47% (range = 30%–58%) of the observed decline. With no tobacco control, incidence would have declined only 56%, suggesting that lower smoking initiation and higher cessation rates observed after the 1960s accelerated the relative decline in cancer incidence by 7% (range = 0%–21%). With continued risk factor trends, incidence is projected to decline an additional 47% between 2008 and 2040, the majority of which will be attributable to H. pylori and smoking (81%; range = 61%–100%). Limitations include assuming all other risk factors influenced gastric carcinogenesis as one factor and restricting the analysis to men.
Conclusions
Trends in modifiable risk factors explain a significant proportion of the decline of intestinal-type NCGA incidence in the US, and are projected to continue. Although past tobacco control efforts have hastened the decline, full benefits will take decades to be realized, and further discouragement of smoking and reduction of H. pylori should be priorities for gastric cancer control efforts.
Please see later in the article for the Editors' Summary
Editors' Summary
Background
Cancer of the stomach (gastric cancer) is responsible for a tenth of all cancer deaths world-wide, with an estimated 700,000 people dying from this malignancy every year, making it the second most common cause of global cancer-related deaths after lung cancer. Unfortunately, the projected global burden of this disease estimate that deaths from gastric cancer will double by 2030. Gastric cancer has a poor prognosis with only a quarter of people with this type of cancer surviving more than five years. In order to reduce deaths, it is therefore of utmost importance to identify and reduce the modifiable risk factors associated with gastric cancer. Smoking and chronic gastric infection with the bacteria Helicobacter pylori (H. pylori), are known to be two common modifiable risk factors for gastric cancer, particularly for a type of gastric cancer called intestinal-type noncardia gastric adenocarcinoma (NCGA), which occurs at the distal end of the stomach and accounts for more than half of all cases of gastric cancer in US men.
Why Was This Study Done?
H. pylori initiates a precancerous process, and so infection with this bacteria can increase intestinal-type NCGA risk by as much as 6-fold while smoking doubles cancer risk by advancing increasing progression of existing lesions. Changes in these two risk factors over the past century (especially following the US Surgeon General's Report on Smoking and Health in 1964) have led to a dramatic decline in the rates of gastric cancer in US men. Understanding the combined effects of underlying risk factor trends on health outcomes for intestinal-type NCGA at the population level can help to predict future cancer trends and burden in the US. So in this study, the researchers used a mathematical model to estimate the contribution of H. pylori and smoking trends on the decline in intestinal-type NCGA incidence in US men.
What Did the Researchers Do and Find?
The researchers used birth cohorts derived from data in two national databases, the National Health and Nutrition Examination Survey (NHANES) and National Health Interview Survey (NHIS) to develop a population-based model of intestinal-type NCGA. To ensure model predictions were consistent with epidemiologic data, the researchers calibrated the model to data on cancer and precancerous lesions and using the model, projected population outcomes between 1978 and 2040 for a base-case scenario (in which all risk factor trends were allowed to vary over time). The researchers then evaluated alternative risk factors scenarios to provide insights on the potential benefit of past and future efforts to control gastric cancer.
Using these methods, the researchers estimated that the incidence of intestinal-type NCGA (standardized by age) fell from 11.0 to 4.4 per 100,000 men between 1978 and 2008, a drop of 60%. When the researchers incorporated only H. pylori prevalence and smoking trends into the model (both of which fell dramatically over the time period) they found that intestinal-type NCGA incidence fell by only 28% (from 12.7 to 9.2 per 100,000 men), suggesting that H. pylori and smoking trends are responsible for 47% of the observed decline. The researchers found that H. pylori trends alone were responsible for 43% of the decrease in cancer but smoking trends were responsible for only a 3% drop. The researchers also found evidence that after the 1960s, observed trends in lower smoking initiation and higher cessation accelerated the decline in intestinal-type NCGA incidence by 7%. Finally, the researchers found that intestinal-type NCGA incidence is projected to decline an additional 47% between 2008 and 2040 (4.4 to 2.3 per 100,000 men) with H. pylori and smoking trends accounting for more than 80% of the observed fall.
What Do These Findings Mean?
These findings suggest that, combined with a fall in smoking rates, almost half of the observed fall in rates of intestinal-type NCGA cancer in US men between 1978 and 2008 was attributable to the decline in infection rates of H. pylori. Rates for this cancer are projected to continue to fall by 2040, with trends for both H. pylori infection and smoking accounting for more than 80% of the observed fall, highlighting the importance of the relationship between risk factors changes over time and achieving long-term reduction in cancer rates. This study is limited by the assumptions made in the model and in that it only examined one type of gastric cancer and excluded women. Nevertheless, this modeling study highlights that continued efforts to reduce rates of smoking and H. pylori infection will help to reduce rates of gastric cancer.
Additional Information
Please access these Web sites via the online version of this summary at http://dx.doi.org/10.1371/journal.pmed.1001451.
The National Cancer Institute gives detailed information about gastric cancer
The Gastric Cancer Foundation has information on gastric cancer for patients and professionals
Cancer Research UK explains types of gastric cancer
doi:10.1371/journal.pmed.1001451
PMCID: PMC3660292  PMID: 23700390
18.  Lung cancer trends: smoking, obesity, and sex assessed in the Staten Island University’s lung cancer patients 
Introduction
The incidence of lung cancer in the United States decreased by 1.8% from 1991 to 2005 while it increased by 0.5% in females. We assessed whether nonsmokers afflicted with lung cancer at Staten Island University Hospital are disproportionately female in comparison to national averages. We also evaluated different factors including race, histology, and body mass index (BMI) in correlation with smoking history.
Methods
A retrospective chart review was conducted from 2005 to 2011 on 857 patients. Patients were divided into two groups according to their smoking status: current or ever-smokers, and former or never-smokers. A chi-square test for categorical data and multivariate logistic regression analyses was used to study the relation between BMI and the other clinical and demographic data.
Results
Forty-nine percent of patients were men and 51% were women with a mean age at diagnosis of 67.8 years. Current smokers were most common (50.2%) followed by ever-smokers (18.2%), former smokers (15.8%) and never-smokers (15.6%). Forty eight percent had stage IV lung cancer upon presentation. Never-smokers with lung cancer were 24 times more likely to be females. However, the proportion of female former smokers (31.6%) was lower than the proportion of male former smokers (68.4%) (P=0.001). There was no significant association between American Joint Committee on Cancer (AJCC) stage, sex, race, and histological type in the two smoking groups. Current/ever-smokers tended to be younger at age of diagnosis (P=0.0003). BMI was lower in the current/ever-smokers (26.8 kg/m2) versus former/never-smokers (28.8) in males (P=0.0005). BMI was significantly higher in males (30.26) versus females (25.25) in the never-smoker category (P=0.004). Current smokers, compared to others, had a lower BMI in males (26.4 versus 28.3; P=0.0001) and females (25.5 versus 26.9; P=0.013) but the mean BMI for all groups was in the overweight/obese range.
Conclusion
Our population of lung cancer patients although demographically distinct, reflects a similar proportion of afflicted nonsmokers to the national population. Smoking is a major risk factor for lung cancer, but there is also a possible direct correlation with BMI that would support obesity as a potential risk factor for lung cancer.
doi:10.2147/IJGM.S55806
PMCID: PMC4085324  PMID: 25061333
lung; cancer; smoking; obesity; BMI; Staten Island
19.  Smoking and Smoking Cessation in Relation to Mortality 
Context
Smoking causes death in many ways, but the rate of risk reduction after quitting, compared to continuing to smoke, is uncertain. There is inadequate or insufficient evidence to infer the presence or absence of a causal relationship between smoking and ovarian cancer and colorectal cancer.
Objective
To assess the relation between cigarette smoking and smoking cessation on total and cause-specific mortality in women.
Design, Setting, and Participants
Prospective observational study of 104,519 female participants in the Nurses’ Health Study followed from 1980 to 2004.
Main Outcome Measure
Hazard ratios for total mortality, further categorized into vascular and respiratory diseases, cancers and other causes.
Results
A total of 12483 deaths occurred in this cohort, 4485 (35.9%) among never smokers, 3602 (28.9%) among current smokers, and 4396 (35.2%) among past smokers. Compared to never smokers, current smokers had an increased risk of total mortality (hazard ratio = 2.81, 95% confidence interval (CI) = 2.68–2.95) and all major cause-specific mortality evaluated. The hazard ratio for cancers classified by the 2004 Surgeon General’s report to be smoking-related was 7.25 (CI:6.43–8.18) and for other cancers, 1.58 (CI:1.45–1.73). The hazard ratio for colorectal cancer was 1.63 (CI:1.29–2.05) for current smokers and 1.23 (CI:1.02–1.49) for former smokers, compared to never smokers. A significant association was not observed for ovarian cancer. Significant trends were observed for earlier age at initiation for total mortality (P=0.003), respiratory disease mortality (P=0.001), and all smoking-caused cancer mortality (P=0.001). The excess risk for all-cause mortality decreases to the level of a never smoker 20 years after quitting, with different timeframes for risk reduction observed across outcomes. Approximately 64% of deaths among current smokers and 28% of deaths among former smokers were attributable to cigarette smoking.
Conclusions
Most of the excess risk of vascular mortality due to smoking can be eliminated rapidly upon cessation and within 20 years for lung diseases. Postponing the age of smoking initiation has a dramatic impact on risk of respiratory disease, lung cancer, and other smoking-caused cancer deaths and little effect on other cause-specific mortality. These data suggest that smoking increases the risk of colorectal cancer mortality but not ovarian cancer mortality.
doi:10.1001/jama.299.17.2037
PMCID: PMC2879642  PMID: 18460664
20.  Overall obesity, abdominal adiposity, diabetes and cigarette smoking in relation to the risk of pancreatic cancer in two Swedish population-based cohorts 
British Journal of Cancer  2005;93(11):1310-1315.
We examined the associations of body mass index (BMI), waist circumference, a history of diabetes, and cigarette smoking with risk of pancreatic cancer among 37 147 women and 45 906 men followed up during 560 666 person-years in the Swedish Mammography Cohort and the Cohort of Swedish Men; 136 incident cases of pancreatic cancer were diagnosed. The multivariate rate ratio (RR) of pancreatic cancer for obese women and men (BMI ⩾30 kg/m2) was 1.81 (95% CI: 1.04–3.15) compared to those with a BMI of 20–25 kg/m2. For a difference of 20 cm (about two standard deviations) in waist circumference, the multivariate RRs were 1.32 (95% CI: 0.73–2.37) among women and 1.74 (95% CI: 1.00–3.01) among men. Pancreatic cancer risk was associated with history of diabetes (multivariate RR: 1.88; 95% CI: 1.09–3.26) and cigarette smoking (multivariate RR for current compared with never smokers: 3.06; 95% CI: 1.99–4.72). Current smokers of ⩾40 pack-years had a five-fold elevated risk compared with never smokers. Risk among past smokers approached the RR for never smokers within 5–10 years following smoking cessation. Findings from this prospective study support positive relationships of overall obesity, abdominal adiposity, diabetes and smoking with risk of pancreatic cancer.
doi:10.1038/sj.bjc.6602868
PMCID: PMC2361517  PMID: 16288300
anthropometry; body mass index; cohort studies; diabetes mellitus; pancreatic neoplasms; obesity; prospective studies; smoking; smoking cessation
21.  Serum uric acid and the risk of respiratory disease: a population-based cohort study 
Thorax  2014;69(11):1021-1026.
Introduction
Uric acid is the most abundant molecule with antioxidant properties found in human blood serum. We examined the relationship between serum uric acid and the incidence of respiratory disease including any effect modification by smoking status.
Methods
A cohort with serum uric acid measured between 1 January 2000 and 31 December 2012 was extracted from The Health Improvement Network primary care research database. New diagnoses of COPD and lung cancer were ascertained based on diagnostic codes entered into the medical records.
Results
During 1 002 496 person years (PYs) of follow-up, there were 3901 COPD diagnoses and 1015 cases of lung cancer. After multivariable adjustment, strong interactions with smoking status were detected (p<0.001) for both outcomes with significant negative relationships between serum uric acid and respiratory disease for current smokers but no strong relationships for never-smokers or ex-smokers. The relationships were strongest for lung cancer in heavy smokers (≥20 cigarettes per day) with predicted incidence rates 97 per 10 000 PYs (95% CI 68 to 126) in the lowest serum uric acid quintile (100–250 µmol/L) compared with a predicted 28 per 10 000 PYs (95% CI 14 to 41) in the highest quintile (438–700 µmol/L).
Conclusions
Low levels of serum uric acid are associated with higher rates of COPD and lung cancer in current smokers after accounting for conventional risk factors.
doi:10.1136/thoraxjnl-2014-205271
PMCID: PMC4215274  PMID: 24904021
COPD epidemiology; Lung Cancer; Oxidative Stress; Tobacco and the lung
22.  Particulate Matter Air Pollution Exposure, Distance to Road, and Incident Lung Cancer in the Nurses’ Health Study Cohort 
Environmental Health Perspectives  2014;122(9):926-932.
Background: A body of literature has suggested an elevated risk of lung cancer associated with particulate matter and traffic-related pollutants.
Objective: We examined the relation of lung cancer incidence with long-term residential exposures to ambient particulate matter and residential distance to roadway, as a proxy for traffic-related exposures.
Methods: For participants in the Nurses’ Health Study, a nationwide prospective cohort of women, we estimated 72-month average exposures to PM2.5, PM2.5–10, and PM10 and residential distance to road. Follow-up for incident cases of lung cancer occurred from 1994 through 2010. Cox proportional hazards models were adjusted for potential confounders. Effect modification by smoking status was examined.
Results: During 1,510,027 person-years, 2,155 incident cases of lung cancer were observed among 103,650 participants. In fully adjusted models, a 10-μg/m3 increase in 72-month average PM10 [hazard ratio (HR) = 1.04; 95% CI: 0.95, 1.14], PM2.5 (HR = 1.06; 95% CI: 0.91, 1.25), or PM2.5–10 (HR = 1.05; 95% CI: 0.92, 1.20) was positively associated with lung cancer. When the cohort was restricted to never-smokers and to former smokers who had quit at least 10 years before, the associations appeared to increase and were strongest for PM2.5 (PM10: HR = 1.15; 95% CI: 1.00, 1.32; PM2.5: HR = 1.37; 95% CI: 1.06, 1.77; PM2.5–10: HR = 1.11; 95% CI: 0.90, 1.37). Results were most elevated when restricted to the most prevalent subtype, adenocarcinomas. Risks with roadway proximity were less consistent.
Conclusions: Our findings support those from other studies indicating increased risk of incident lung cancer associated with ambient PM exposures, especially among never- and long-term former smokers.
Citation: Puett RC, Hart JE, Yanosky JD, Spiegelman D, Wang M, Fisher JA, Hong B, Laden F. 2014. Particulate matter air pollution exposure, distance to road, and incident lung cancer in the Nurses’ Health Study Cohort. Environ Health Perspect 122:926–932; http://dx.doi.org/10.1289/ehp.1307490
doi:10.1289/ehp.1307490
PMCID: PMC4154215  PMID: 24911062
23.  Cigarette tar yields in relation to mortality from lung cancer in the cancer prevention study II prospective cohort, 1982-8 
BMJ : British Medical Journal  2004;328(7431):72.
Objective To assess the risk of lung cancer in smokers of medium tar filter cigarettes compared with smokers of low tar and very low tar filter cigarettes.
Design Analysis of the association between the tar rating of the brand of cigarette smoked in 1982 and mortality from lung cancer over the next six years. Multivariate proportional hazards analyses used to assess hazard ratios, with adjustment for age at enrolment, race, educational level, marital status, blue collar employment, occupational exposure to asbestos, intake of vegetables, citrus fruits, and vitamins, and, in analyses of current and former smokers, for age when they started to smoke and number of cigarettes smoked per day.
Setting Cancer prevention study II (CPS-II).
Participants 364 239 men and 576 535 women, aged ≥ 30 years, who had either never smoked, were former smokers, or were currently smoking a specific brand of cigarette when they were enrolled in the cancer prevention study.
Main outcome measure Death from primary cancer of the lung among participants who had never smoked, former smokers, smokers of very low tar (≤ 7 mg tar/cigarette) filter, low tar (8-14 mg) filter, high tar (≥ 22 mg) non-filter brands and medium tar conventional filter brands (15-21 mg).
Results Irrespective of the tar level of their current brand, all current smokers had a far greater risk of lung cancer than people who had stopped smoking or had never smoked. Compared with smokers of medium tar (15-21 mg) filter cigarettes, risk was higher among men and women who smoked high tar (≥ 22 mg) non-filter brands (hazard ratio 1.44, 95% confidence interval 1.20 to 1.73, and 1.64, 1.26 to 2.15, respectively). There was no difference in risk among men who smoked brands rated as very low tar (1.17, 0.95 to 1.45) or low tar (1.02, 0.90 to 1.16) compared with those who smoked medium tar brands. The same was seen for women (0.98, 0.80 to 1.21, and 0.95, 0.82 to 1.11, respectively).
Conclusion The increase in lung cancer risk is similar in people who smoke medium tar cigarettes (15-21 mg), low tar cigarettes (8-14 mg), or very low tar cigarettes (≤ 7 mg). Men and women who smoke non-filtered cigarettes with tar ratings ≥ 22 mg have an even higher risk of lung cancer.
doi:10.1136/bmj.37936.585382.44
PMCID: PMC314045  PMID: 14715602
24.  Smoking and risk of amyotrophic lateral sclerosis: a pooled analysis of five prospective cohorts 
Archives of Neurology  2011;68(2):207-213.
Objective
Cigarette smoking has been proposed as a risk factor for amyotrophic lateral sclerosis (ALS), but epidemiological studies supporting this hypothesis have been small and mostly retrospective. We therefore prospectively examined the relation between smoking and ALS in five well-established large cohorts.
Design
Five prospective cohorts with study-specific follow-up ranging from 7 to 28 years.
Subjects
Participants of the Nurses’ Health Study (NHS), the Health Professionals Follow-up Study (HPFS), the Cancer Prevention Study II Nutrition Cohort, the Multiethnic Cohort, and the NIH-American Association of Retired Persons Diet and Health Study.
Main Outcome Measure
ALS deaths identified through the National Death Index. In NHS and HPFS confirmed non-fatal incident ALS was also included.
Results
832 participants with ALS were documented among 562,804 men and 556,276 women. Smokers had a higher risk of ALS than never smokers: age- and sex-adjusted relative risks=1.44 (95%CI: 1.23–1.68;p<0.0001) for former smokers, and 1.42 (95%CI: 1.07–1.88;p=0.016) for current smokers. Although the risk of ALS was positively associated with pack-years smoked (p<0.0001), duration (9% increase for each 10-years of smoking; p=0.006) and cigarettes smoked per day (10% increase for 10 cigarettes per day; p<0.001), these associations did not persist when never smokers were excluded. However, among ever-smokers, risk of ALS increased as age at smoking initiation decreased (p=0.028).
Conclusions
Results of this large longitudinal study support the hypothesis that cigarette smoking increases the risk of ALS. The potential importance of age at smoking initiation and the lack of a dose-response deserve further investigation.
doi:10.1001/archneurol.2010.367
PMCID: PMC3319086  PMID: 21320987
25.  Higher Rates of Clostridium difficile Infection among Smokers 
PLoS ONE  2012;7(7):e42091.
Objectives
Cigarette smoking has been shown to be related to inflammatory bowel disease. We investigated whether smoking affected the probability of developing Clostridium difficile infection (CDI).
Methods
We conducted a longitudinal study of 16,781 older individuals from the nationally representative Health and Retirement Study. Data were linked to files from the Centers for Medicare and Medicaid Services.
Results
Overall, the rate of CDI in older individuals was 220.6 per 100,000 person-years (95% CI 193.3, 248.0). Rates of CDI were 281.6/100,000 person-years in current smokers, 229.0/100,000 in former smokers and 189.1/100,000 person-years in never smokers. The odds of CDI were 33% greater in former smokers (95% CI: 8%, 65%) and 80% greater in current smokers (95% CI: 33%, 145%) when compared to never smokers. When the number of CDI-related visits was evaluated, current smokers had a 75% increased rate of CDI compared to never smokers (95% CI: 15%, 167%).
Conclusions
Smoking is associated with developing a Clostridium difficile infection. Current smokers have the highest risk, followed by former smokers, when compared to rates of infection in never smokers.
doi:10.1371/journal.pone.0042091
PMCID: PMC3407081  PMID: 22848714

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