The results indicate that disparities in CRC incidence and mortality between African Americans and whites in Wisconsin are large and have increased over the last decade. These results are similar in trajectory to those observed at the national level over the same period, although the scale of change in Wisconsin was much larger. For the U.S. as a whole, CRC mortality rates decreased for both whites and African Americans from 1999 to 2006, but the rate ratio increased from 1.4 to 1.5. National CRC incidence rates have also decreased, but the relative disparity has remained stable at 1.2 (32)
. The state-level data are critical to understanding where Wisconsin is in its effort to reduce the burden of CRC, and to informing research and interventions for CRC prevention and control.
The reasons for the alarming increase in disparities in CRC mortality and incidence between African Americans and whites in Wisconsin are unknown, but may be due to changes in risk factors in these two populations, such as obesity. Results from the Wisconsin Behavioral Risk Factor Survey reveal that between 2000 and 2009, overweight/obesity rates among African Americans increased 26% (from 64% to 86%). Overweight/obesity rates also increased among whites, but the increase was much smaller (11%, from 58% to 65%) (33)
Low socioeconomic status has been shown to be associated with an increase in the incidence of and poorer survival from CRC (34)
. The fact that in Wisconsin, African Americans are more likely to live in poverty and less likely to have graduated from high school than whites (36)
may explain some of the observed CRC disparities. Cancer disparities have also been explained by differential access to screening, diagnosis, and treatment (2)
. African American residents of Wisconsin are twice as likely to be uninsured as whites (36)
. It is thus possible that African Americans are less likely to receive appropriate CRC screening (18)
, appropriate, timely treatment for CRC (15)
, or services known to prevent CRC (41)
. The staging distribution presented here shows that there have been increasing numbers of limited stage CRC diagnosed amongst African Americans, suggesting a possible screening effect. Finally, health care access has also improved for African Americans. In 1996-2000, the uninsurance rate among African Americans was 17% (47)
, compared to 13% in 2001-2005 (46)
A number of limitations should be considered when interpreting the results of this study. First, the scope is limited to differences in CRC 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 the present study 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. The African American population in Wisconsin has been stable in numbers for some time in Wisconsin, and is concentrated in larger urban areas, chiefly Milwaukee. This is in contrast to southern United States where African Americans are distributed in rural and urban areas and not heavily concentrated. Thus, in Wisconsin migration is not a large issue for the African American population in such a way to make raise concern about selection bias.
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. WCRS has made data collection improvements and suggestions in determining the race and ethnicity of cancer cases (the numerator for incidence rates). However, 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, and facilities vary in the methods used for collecting racial and ethnic data. Especially when the number of cases is relatively small, the quality of data collection and reporting can greatly impact annual incidence numbers and rates. Cancer registry stage is also reported in a format different from the American Joint Commission on Cancer TNM staging that clinicians use in practice, so one cannot compare the two directly. The WCRS does not report data on geographic location, age distribution or socioeconomic status. Additionally, the treatment data collected in the WCRS is not reliably validated and so is not reported.
In summary, disparities in CRC incidence and mortality between African Americans and whites in Wisconsin are large and have worsened over the period 1995 to 2006. Statewide action to reduce CRC disparities must start with this evidence. First, African Americans may fall into a higher risk group warranting earlier initiation of colorectal screening than the currently recommended starting age for all average risk adults. There is also promise in efforts to reduce exposure to risk factors and improve access to appropriate screening, treatment, and prevention (2)
among all Wisconsin residents, and in particular among African Americans. Patient navigation is one such tool (43)
. Care must be taken that any plan carefully balance resources and set appropriate priorities to target inequities in CRC burden.