The disparity between black women and white women in breast cancer survival has not changed appreciably since the early 1990s, and it appears to be related primarily to differences between the two racial groups at presentation rather than to treatment differences, according to a report in the July 24/31 issue of JAMA.
These are the findings of a large, population-based study using an innovative statistical approach to tease out the complex interactions among demographic, clinical, and treatment differences between the races.
"Our results suggest that it may be difficult to eliminate the racial disparity in survival ... unless differences in presentation can be reduced," said Dr. Jeffrey H. Silber of the Center for Outcomes Research at Children’s Hospital of Philadelphia and his associates.
Dr. Jeffrey Silber
The researchers analyzed information from the Surveillance, Epidemiology and End Results (SEER)-Medicare database to assess the racial disparity in 5-year breast cancer survival among women older than 65 years at diagnosis in 1991-2005.To do so, they used rigorous matching methods in three sequential analyses to compare 7,375 black patients with white control subjects selected from a pool of 99,898 white patients.
The black women first were compared with white women who had similar demographic traits (age, year of diagnosis, and SEER site), then with white patients who had similar clinical presentations (comorbidities, tumor stage, and other tumor factors), and finally with white patients who had similar treatment (specifics of surgery, radiotherapy, and chemotherapy).
"The three matched white groups sequentially remove aspects of the [racial] disparity while leaving other aspects in place, so as to develop an understanding of how the disparity occurs," the investigators noted (JAMA 2013;310:389-97).
There were four major findings:
First, 5-year breast cancer survival improved somewhat in both races over time, but the disparity between black women and white women remained constant.
Second, when the women were matched for demographic characteristics at presentation, 5-year survival was 68.8% for white women and 55.9% for black women, an absolute difference of nearly 13%, which represents approximately 3 years of life. In other words, compared with white women of the same age, year of diagnosis, and geographical location, black women still had a significantly lower 5-year breast cancer survival. Thus, demographic differences explain only a small part of the racial disparity.
Third, when the women were matched for clinical traits at presentation, this disparity in 5-year survival dropped to 4.4%, which represents approximately 1 year. This is a smaller but still significant difference between black women and white women who present with the same clinical picture.
Fourth, when the women were matched for treatment factors, this disparity only decreased slightly. "Hence, treatment differences explained only 0.81% of the 12.9% difference in 5-year survival," Dr. Silber and his associates said.
Most of the disparity in survival could be attributed to the poorer health of black women at presentation. Black women were markedly less likely than were white women to have seen a primary care provider during the preceding year and were significantly less likely to have undergone recent screening for breast cancer, colon cancer, or high cholesterol.
Black women also were significantly more likely than white women to have comorbid conditions. "Some of the effectiveness of cancer treatment ... may be blunted by other health problems" or by the treatment of those health problems, the investigators said.
Finally, black women were more likely than were white women to present with advanced breast cancer and worse biological features, such as larger tumor size and less favorable receptor status. The mean interval between diagnosis and the first treatment also was significantly longer for black women than for white women, they added.
This study was supported by the Agency for Healthcare Research and Quality, the U.S. Department of Health and Human Services, and the National Science Foundation. No relevant conflicts of interest were reported.