The incidence of advanced breast cancer diagnosis among African American women remained 30 percent to 90 percent higher compared to white women between 1992 and 2004, according to new findings by Hutchinson Center researchers. They also found the disparity in the incidence of advanced colorectal cancer actually widened over this time period as rates fell among whites but increased slightly among African Americans. The findings were published online in the inaugural issue of the journal Hormones and Cancer.
“While we could not determine the exact contributors to the trends we saw in this study, it is interesting to note that for breast cancer, mammographic screening rates were quite similar among African American and white women in the United States during the time period we studied. This suggests that factors other than screening may be contributing to this persistent disparity, including differences in both lifestyle and genetics,” said senior author Dr. Chris Li of the Public Health Sciences Division.
Li said a potential explanation for this disparity is that African American women tend to have more aggressive tumors that are more difficult to detect and treat as compared to non-Hispanic white women.
Overall, rates of advanced breast cancer remained essentially constant among women of both races throughout the study period, affecting about 18 out of 100,000 black women and 12 out of 100,000 white women.
The study also looked at rates of advanced-stage colorectal and prostate cancer in an attempt to deduce how screening practices may have impacted the magnitude of racial disparities in these malignancies during this 12-year period, an era of increased use of breast, colorectal and prostate cancer screening in the U.S.
Colorectal endoscopy screening rates may factor
For colorectal cancer, the researchers saw a widening of the racial disparity gap. Late-stage incidence rates among non-Hispanic whites declined over time but increased somewhat among African Americans. “It is possible that differing rates of colorectal endoscopy screening between African American and non-Hispanic whites could contribute to this widening disparity,” said lead author Jean McDougall, an epidemiology doctoral student at the University of Washington School of Public Health.
The African American colorectal cancer patients in this study were slightly younger at diagnosis and were more likely to be female as compared to whites. The relative risk of advanced colorectal cancer was significantly elevated in African Americans throughout the study period. In 1992, they were 60 percent more likely to be diagnosed with late-stage colorectal cancer as compared to whites, and by 2004 that likelihood had doubled.
Study links screening awareness to lower prostate cancer rates
However, for prostate cancer, the disparity gap narrowed somewhat over time, as advanced-stage prostate cancer incidence rates declined for both African American and non-Hispanic whites. The incidence of late-stage prostate cancer among African American men fell from 50 cases in 100,000 at the start of the study to 19.8 cases in 100,000 in 2004. This level was still three times higher than that of white men, but it was a significant decline nonetheless.
“During this time period it became increasingly apparent that prostate cancer was an important public health problem in the African American community and there was a lot of effort to address this issue by raising awareness of screening,” Li said. “I think that maybe we’re seeing some of the benefits of that work here.”
For the study, the researchers analyzed data from 12 population-based urban cancer registries throughout the continental U.S. and Hawaii, representing about 14 percent of the population. The study did not evaluate late-stage cancer rates among Asians/Pacific Islanders, American Indians/Alaska Natives or those of Hispanic ethnicity due to insufficient numbers of cases.
Because the study was based on population-based data rather than individual data that would reflect tumor biology or screening practices, the authors caution that the findings cannot predict individual risk but should be interpreted as a broad view of cancer trends over time.
“Epidemiologic studies such as this one are an important first step in understanding trends in disease rates on a population level,” McDougall said. “However, we cannot draw strong conclusions regarding the factors contributing to the trends observed from this study, as its goal was to describe trends over time without using detailed data on individual cases and the complex factors that contribute to disease.”
The authors concluded that African Americans continue to have a disproportionately high cancer burden, and therefore “continued multipronged efforts aimed at improving access to breast, colorectal and prostate cancer prevention, screening, diagnostics and treatment services are warranted.”