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Cancer incidence and mortality rates have decreased over the last few decades, yet not all groups have benefited equally from these successes. This has resulted in increased disparities in cancer burden among various population groups.
This study examined trends in absolute and relative disparities in overall cancer incidence and mortality rates between African American and white residents of Wisconsin during 1995 to 2006.
Cancer incidence data were obtained from the Wisconsin Cancer Reporting System. Mortality data were accessed from the National Center for Health Statistics’ public use mortality file. Trends in incidence and mortality rates during 1995–2006 for African Americans and whites were calculated and changes in relative disparity were measured using rate ratios.
With few exceptions, African American incidence and mortality rates were higher than white rates in every year of the period 1995–2006. Although cancer mortality and incidence declined for both groups over the period, relative racial disparities in rates persisted over the period and account for about a third of African American cancer deaths.
Elimination of cancer health disparities will require further research into the many contributing factors, as well as into effective interventions to address them. In Wisconsin, policy makers, health administrators, and healthcare providers need to balance resources carefully and set appropriate priorities to target racial inequities in cancer burden.
Cancer health disparities are a major public health concern nationally and in Wisconsin. Although treatments for cancer are improving and cancer mortality is decreasing1, 2, not all Americans benefit equally from these successes3, 4. Many population groups in Wisconsin and nationwide, often identified by race, ethnicity, socioeconomic status, and geography, experience a greater burden of cancer along the continuum from prevention to detection, diagnosis, treatment, survivorship, and end-of-life. For example, recent national data from an American Cancer Society study5 showed that compared to white men, African American men had a 19% higher all site cancer incidence rate and 37% higher mortality rate. In the state of Wisconsin, previous reports have revealed similar racial and ethnic disparities in cancer mortality and incidence2, 6–10. The report Wisconsin Cancer Incidence and Mortality 2000–2004 showed that whites had lower all site cancer incidence and mortality rates than any other racial group, except Asian/Pacific Islanders8. Another study found that disparities in cancer incidence and mortality between African Americans and whites were greater in Wisconsin than in the rest of the United States9. Statewide studies of cancer outcomes by socioeconomic status and geography in Wisconsin are limited2, 11, 12.
National organizations such as the National Cancer Institute, US Department of Health and Human Services, and the American Cancer Society have targeted the elimination of health disparities. In Wisconsin, eliminating health disparities is an overarching goal embodied in Healthiest Wisconsin 201013 and is the motivation for the Wisconsin Minority Health Program6. Cancer health disparities are also a prominent, cross cutting issue in Wisconsin’s Comprehensive Cancer Control Plan14.
Monitoring trends in cancer incidence and mortality is an important part of any coordinated state plan to reduce disparities. This information is useful to cancer prevention programs, clinicians, and policy makers who seek to reduce the burden of cancer. At the national level, there is some evidence that the African American/white disparity in cancer rates has narrowed15. There is no such trend data for Wisconsin: previously published reports on cancer health disparities in the state2, 6–10 have combined several years of data in order to report on multiple racial groups. While limited to a comparison between African Americans and whites, the two largest race groups in the state, the present study is unique in providing annual rates over a 12-year period as well as calculating trends in incidence and mortality. The decision to focus on disparities between African Americans and whites and not other racial or ethnic groups was based on the statistical limitations inherent in analyzing rare events in small populations, as Wisconsin’s minority populations are relatively small in number and geographically clustered.
The purpose of this study is to provide information about trends over time in cancer incidence and mortality among African Americans and whites in Wisconsin. This study features the latest data available in March 2010 covering Wisconsin cancer cases and deaths, displayed by single years for the two largest race groups in the state. Finally, this study estimates the potential burden experienced by African Americans by showing how many deaths would have occurred if African Americans experienced the same age-specific cancer death rates as whites.
We obtained incidence data from the Wisconsin Cancer Reporting System for the period 1995 to 2006, the most recent year for which data were available. As required by state law, cancer cases are reported to the Cancer Reporting System by Wisconsin hospitals, clinics, and physician offices. All invasive and noninvasive malignant tumors, except basal and squamous cell carcinomas of the skin and in situ cancers of the cervix uteri, are reportable to the Cancer Reporting System. Incidence rates were age-adjusted using the 2000 US standard population and were calculated using NCI’s SEER*Stat software.
Mortality data used in this study reflect Wisconsin resident death records from the Vital Records Section, Wisconsin Department of Health Services. We accessed mortality data from the National Center for Health Statistics (NCHS) public use data file of Wisconsin deaths for the period 1995 to 2006. Population data used in calculating cancer rates are obtained periodically by NCHS from the Census Bureau; those used in this study were age-adjusted to the 2000 US standard population16. We used the SEER*Stat software package to calculate mortality rates. We also applied race categories used by NCHS17.
First, we plotted the observed annual incidence and mortality rates over the period 1995 to 2006 for all Wisconsin residents, by race and gender. Next, we plotted trend lines of the incidence and mortality data, by race and gender, using slopes and intercepts derived from ordinary least squares regressions. Then we calculated the ratio of the African American incidence and mortality rates to the white rates (rate ratio) in 1995 and 2006, based on the 1995–2006 trend line. This ratio constitutes our measure of relative disparity18, and was compared between the beginning and the end of the period.
In order to measure the extent of cancer disparities in mortality, we constructed a hypothetical situation in which African Americans experienced the cancer mortality rates observed among whites. We calculated simulated deaths by multiplying the age-specific mortality rates observed among whites by the African American population in each five-year age group. We used the ratio of modeled to observed deaths among African Americans as an estimate of excess mortality, or deaths that would have been averted if African Americans had experienced the lower age-specific death rates of whites.
During 1995–2006, cancer was diagnosed in 319,958 Wisconsin residents, including 303,072 whites and 11,345 African Americans. Overall age-adjusted cancer incidence decreased 5.0% from 476 per 100,000 in 1995 to 452 per 100,000 in 2006. For both African Americans and whites, incidence also decreased over the period. However, an absolute disparity in rates persisted, with African American rates higher than white rates in every year (Figure 1). Relative disparity, measured using the ratio of the African American incidence rate to the white incidence rate, persisted over the period at 1.15 in 1995 and 1.14 in 2006 (Table 1). (Note that in all cases, the rate ratios for 1995 and 2006 were not significantly different at the p<.05 level.)
From 1995 to 2006, there were 128,920 deaths due to cancer among Wisconsin residents, including 122,866 whites and 4,899 African Americans. Overall age-adjusted cancer mortality declined 9.5% from 200 per 100,000 in 1995 to 181 per 100,000 in 2006. While mortality decreased over the period among both African Americans and whites, the African American rate was greater than the white rate in every year (Figure 1). The relative disparity persisted over the period, as evidenced by the rate ratio of 1.39 in 1995 and 1.40 in 2006 (Table 1). Moreover, if African Americans had experienced the same age-specific mortality rates as whites, about one third of African American cancer deaths would have been averted in 1995 and 2006 (Table 2).
From 1995 to 2006, cancer was diagnosed in 165,660 Wisconsin men, including 156,490 whites and 6,189 African Americans. Overall age-adjusted cancer incidence among men decreased 10.0% from 572 per 100,000 in 1995 to 515 per 100,000 in 2006. Incidence also decreased among African Americans and whites. However, an absolute disparity in cancer incidence between African American and white males persisted over the period, with African American rates higher than white rates in all years (Figure 2). The relative disparity between the two groups decreased slightly between 1995 and 2006 (from a rate ratio of 1.34 to 1.27) (Table 1).
During 1995–2006, there were 67,042 deaths due to cancer among Wisconsin men, including 63,766 whites and 2,698 African Americans. The age-adjusted cancer morality rate among men declined 15.9% from 258 per 100,000 in 1995 to 217 per 100,000 in 2006. For both African Americans and whites, mortality decreased over the period, but the African American rate remained greater than the white rate in every year (Figure 2). The relative disparity in overall cancer mortality also persisted over the period (rate ratio 1.54 in 1995 and 1.57 in 2006) (Table 1). If African Americans had experienced the lower age-specific mortality rates of whites, about 40% of cancer deaths among African American men would have been averted in 1995 and 2006 (Table 2).
During 1995–2006, cancer was diagnosed in 154,298 Wisconsin women, including 146,582 whites and 5,156 African Americans. Overall age-adjusted cancer incidence among women decreased 1.9% from 416 per 100,000 in 1995 to 408 per 100,000 in 2006. The incidence rate for white women was higher than for African American women in 1995. However, over the period 1995–2006 (Figure 3), the white rate decreased and the African American rate increased so that in 2006 the incidence rate was essentially the same in each group (406 per 100,000 among African Americans and 407 per 100,000 among whites). Thus, the relative disparity between the two groups increased slightly from a rate ratio of 0.97 in 1995 to 1.02 in 2006 (Table 1).
From 1995 to 2006, there were 61,878 deaths due to cancer among Wisconsin women, including 59,100 whites and 2,201 African Americans. The overall age-adjusted cancer mortality rate among women declined 4.8% from 165 per 100,000 in 1995 to 157 per 100,000 in 2006. The mortality rate among African Americans remained the same and for whites decreased slightly over the period, although the African American rate was consistently higher than the white rate (Figure 3). The relative disparity between African American and white female cancer mortality rates persisted at 1.24 in 1995 to 1.26 in 2006 (Table 1). If African American women had experienced the lower age-specific death rates of whites, about 20% of cancer deaths among African American women in 1995 and 2006 (Table 2).
For all Wisconsin residents, all site cancer incidence and mortality rates decreased over the period 1995–2006. This decline was observed among whites and African American males. For African American females, cancer mortality rates remained constant over the period, while incidence rates increased. There was a persistent absolute disparity in African American and white cancer incidence and mortality rates, with African American rates exceeding white rates in nearly every year. The only exception was African American females, for whom incidence rates started lower than white rates in 1995, but increased to meet the (decreasing) white rate by 2006. The relative disparities in cancer incidence and mortality between African Americans and whites persisted over the period. This result differs from national data which show a recent narrowing in all site cancer disparities15.
Other reports2, 6–10 have also found that African Americans in Wisconsin have a higher risk of developing and dying from cancer than whites. However, these reports aggregated data over several years. Only one of these Wisconsin reports used a measure of relative disparities9, but it did not measure change over time. By measuring trends in rate ratios, the present study provides evidence that, while cancer mortality and incidence have declined in general, Wisconsin has not made sufficient progress towards the overarching goal of eliminating racial disparities13. The elimination of disparities has proven to be a long-term process that may take a generation to achieve19.
Factors known to contribute to racial disparities in cancer incidence and mortality vary by disease site but include differences in exposure to risk factors as well as access to screening, diagnosis, and treatment5. Socioeconomic factors (such as poverty, inadequate education, and lack of health insurance) and their interaction with known risk factors (such as tobacco use, physical inactivity, and obesity) have been shown in some studies to be more important in explaining racial disparities in cancer than biological differences2–4, 20. However, some recent studies have shown genetic and tumor morphology associations with survival and prognosis disparities among racial groups21, 22. Other factors that have been shown to influence racial health disparities include quality of care, exposure to environmental risk factors, and discrimination4, 20, 23, 24. In Wisconsin, African Americans have higher exposure than whites to several factors known to contribute to cancer disparities, including higher rates of tobacco use and obesity, and lower screening rates, lower quality of healthcare, and less insurance coverage6, 14.
In the past decade, there has been increasing discussion of strategies to reduce cancer health disparities. National reports have outlined interventions focused on modifiable risk factors for cancer, such as smoking, physical inactivity, and obesity, the expanded use of recommended screening tests among vulnerable populations, and expanded access to clinical trials20, 24. In 2004 the Trans-Health and Human Services Cancer Health Disparities Progress Review Group stressed the need for community engagement in design of healthcare delivery systems, a culturally competent healthcare work force, more participatory research conducted with communities facing high cancer disparities, and expanded access to health care25.
Modeled after national and state plans, Wisconsin’s Comprehensive Cancer Control Plan14 (WCCC) outlines opportunities to reduce the cancer burden through a variety of initiatives, including prevention, screening and detection, treatment, palliative care, and improved data collection, as well as to reduce cancer health disparities as a cross cutting issue. To meet the state’s prevention needs, several groups are working to reduce the burden of tobacco and improve diet and physical fitness. Smoke Free Wisconsin and many other stakeholders were recently successful in passing a statewide smoking ban in public areas that will take effect in June 2010. The Center for Tobacco Research and Intervention (CTRI) provides cessation assistance for Wisconsin residents who decide to quit smoking. CTRI works with the Wisconsin Department of Public Health’s Tobacco Prevention and Poverty Network to target disparities by improving access to tobacco control resources for lower socioeconomic populations. To reduce disparities in diet and exercise-related factors that affect cancer risk, Wisconsin’s Nutrition and Physical Activity State Plan to Prevent Obesity and Other Chronic Diseases is working to identify and implement culturally sensitive and evidence-based strategies to reduce health disparities.
To meet the state’s cancer screening needs, the WCCC plan seeks to expand colorectal screening for populations facing economic, geographic, or cultural barriers. The Wisconsin Well Women Program provides breast and cervical screening to approximately 12,000 low income, uninsured, and underinsured women each year, of whom approximately 15% are African American women from southeastern Wisconsin. Despite the earnest work by these programs and institutions, more research on effective interventions is needed to overcome cancer disparities such as those identified in this study23, 25.
A number of limitations should be considered when interpreting the results of this study. First, the scope is limited to differences in cancer incidence and mortality rates between African American and whites. The decision to focus on these two groups was determined by the demographic composition of Wisconsin and the rarity of cancer events. Wisconsin has relatively small non-white populations, making the comparisons in this report difficult to replicate between other racial or ethnic groups in the state. Cancer incidence and mortality rates among many minority populations vary widely from year to year. However this variation is likely due to the small size of the population groups rather than real changes in disease burden. Discussion of cancer incidence and mortality trends in Wisconsin’s other minority populations is important and should be featured in future research which identifies and discusses the statistical issues involved in observing rare events in small populations.
Second, WCRS, as a central state cancer registry participating in the National Program of Cancer Registries, maintains a passive system of data collection and therefore, the various reporting facilities are largely responsible for the quality and timeliness of the data submissions to WCRS. Reporting variability may impact the relatively small annual numbers reported in this analysis. In spite of the data collection improvements and suggestions WCRS has made in determining the race and ethnicity of cancer cases (the numerator for incidence rates), it is likely that an unknown degree of misclassification or under-reporting of race still exists. There are no national standards for collecting race data; facilities vary in the methods used for collecting racial and ethnic data. Patients’ race may be recorded on the admission form, physician’s notes, insurance forms, or not recorded at all. Some facilities do not ask patients to self identify or do not collect data for place of birth, although both are strongly recommended by state cancer registries. Especially when the number of cases is relatively small, the quality of data collection and reporting can greatly impact annual incidence numbers and rates.
The results of this research indicate that disparities in cancer incidence and mortality between African Americans and whites in Wisconsin have persisted over the past decade. Elimination of these chronic disparities will require further research into a multitude of contributing factors, as well as into effective intervention strategies. Any solution will require a careful balance of resources and appropriate priorities to target these inequities and engagement of the populations and communities affected23, 25. There is current promise in the Wisconsin programs directed at reducing racial and ethnic disparities in cancer rates. To help inform those programs, data in this report serve to demonstrate the temporal persistence of African Americans’ disproportionate cancer burden.