Men and women had similar ages, whereas women had lower daily energy (kcal) intake, higher intake of fruit and vegetables per 1000 kcal/day, less formal education, drank less alcohol, and were less likely to ever smoke cigarettes, pipes, or cigars than men. In contrast, a higher percentage of women 31,542 (17.1% of 184,623) were current smokers then were men 35,256 (12.6% of 279,214) (). Between October 25, 1995 and December 31, 2003, during 3,334,956 years of follow-up, 6,334 study participants were diagnosed with lung carcinoma (4,097 men and 2,237 women).
In never smokers of cigarettes, the age-standardized incidence rates (per 100,000 person-years) for lung carcinoma were 22.8 (95% confidence interval (CI): 19.0–26.7) for men and 25.4 (95% CI: 21.4–29.5) for women (data not in tables). But, after excluding ever smokers of pipes or cigars from this category, the age-standardized incidence rates became 20.3 (95%CI: 16.3–24.3) for men and 25.3 (95%CI: 21.3–29.3) for women (). From an age adjusted Cox proportional hazards model, women who did not smoke cigarettes, pipes, or cigars had a HR of 1.2 (95% CI: 1.0–1.6) relative to men in this group (data not in tables). After multivariate adjustment for potential confounders, the risk estimate became 1.3 (95%CI: 1.0–1.8).
Adjusted incidence rates, hazard ratios, and 95% confidence intervals for cigarette use and lung carcinoma by sex.
presents incidence rates for lung carcinoma in cigarette smokers, tabulated by years of cessation and typical dose, along with multivariate adjusted hazard ratios directly comparing lung carcinoma risk in women with that for men of the same smoking stratum. Age-adjusted hazard ratios were similar to those with multivariate adjustment (data not shown). Current smokers of > 40 cigarettes (>2 packs per day), had incidence rates of 1,259.2 (95% CI: 1,035.0–1,483.3, 139 carcinomas) in men and 1,308.9 (95% CI: 924.2–1,693.6, 48 carcinomas) in women. Among this group, women had a HR of 1.1 (95% CI: 0.8–1.6) relative to men. Incidence rates were higher in male current smokers of less than 2 packs of cigarettes per day than in female smokers in the same smoking stratum. As an example, women (535 carcinomas) who reported currently smoking 11–20 cigarettes per day had a HR of 0.8 (95% CI: 0.7–0.9) relative to men (605 carcinomas) in this same smoking stratum. For current smokers overall, incidence rates standardized by age and typical smoking dose were 667.4 (95% CI: 635.0–699.9) in men and 584.8 (95%CI: 550.9–618.7) in women (data not in table). After adjusting for typical smoking dose, the HR for currently smoking women relative to currently smoking men was 0.9 (95%CI: 0.8–0.9; data not in table).
For former smokers compared within stratum of time since quitting and usual dose while smoking, men tended to have higher incidence rates than women, but these differences were not statistically significant. As an example, women that reported smoking > 40 cigarettes (>2 packs per day) but stopped smoking more than 10 years ago (51 carcinomas) had a RR of 0.8 (0.6–1.1) relative to men (337 carcinomas) in this group. For former smokers overall, incidence rates standardized by age, years of cessation, and typical smoking dose were 191.7 (95% CI: 183.7–199.7) in men and 185.6 (95% CI: 172.2–198.9) in women (data not in table). From the corresponding Cox proportional hazards model, women had a HR for lung carcinoma of 0.9 (95% CI: 0.9–1.0) relative to men (data not in table).
We also calculated incidence rates standardized by age and all stratums of cigarette use along with pipe or cigar use. After standardization by age and smoking use, incidence rates were 196.3 (95% CI: 190.1–202.5) in men and 190.6 (95% CI: 172.2–209.0) in women. In the corresponding Cox proportional hazards model, women had a HR of 0.9 (95% CI: 0.8–0.9) relative to men for lung carcinoma. We estimate that ever smoking cigarettes, pipes, or cigars accounted for 87% (95% CI, 85–89) of lung carcinoma in men and 85% (95% CI, 82–87) of lung carcinoma in women in this cohort.
Among lung carcinomas with known histologic sub-type (5,126 of 6,334 carcinomas), adenocarcinomas were the most frequent sub-type in never smokers (165 of 206, 80%), ever-smokers (2,562 of 4,920, 52%), men (1,574 of 3,321, 47%), and women (988 of 1,805, 55%). () The hazard ratios associated with smoking varied by histologic type. For example, relative to never smokers, we found higher hazard ratios associated with currently smoking > 1 pack per day for squamous tumors (men: 128.2, 95% CI: 60.1–273.6, 219 carcinomas; women: 139.8, 95% CI: 56.0–349.1, 70 carcinomas) then for adenocarcinomas (men: 17.6 (95% CI: 13.2–23.5, 238 carcinomas; women: 16.4, 95% CI: 12.7–21.1). For adenocarcinomas, never smoking women had borderline increased risk relative to never smoking men (HR for sex, 1.4, 95%CI: 1.0–2.0). The age-standardized incidence rate of adenocarcinoma in never smokers was 12.8 (95% CI: 9.6–16.0) in men and 17.0 (95% CI: 13.7–20.3) in women; among smokers, incidence rates were similar in men and women.
Adjusted incidence rates, hazard ratios, and 95% confidence intervals for cigarette use and lung carcinoma by sex and histology.
We found no significant differences between men and women by cigarette smoking history for undifferentiated and small cell carcinomas. Incidence rates for squamous tumors were twice as high in men as in women for each stratum of cigarette use.