TUESDAY, July 23, 2013 (HealthDay News) -- The survival differences between black women and white women diagnosed with breast cancer has long been recognized, but now a new study focuses on the reasons why black women don't fare as well.
"The vast differences in breast cancer survival between white and black patients relates to the risk factors blacks present with when diagnosed," said lead researcher Dr. Jeffrey H. Silber, the Nancy Abramson Wolfson Endowed Chair in Health Services Research at Children's Hospital of Philadelphia.
"That includes differences in tumor stage and size, and higher rates of chronic health conditions such as diabetes and heart failure," he said.
Although treatment differences, which often are blamed, do play a role, Silber said they did not explain a large portion of the survival disparity he saw in his research.
The study is published in the July 24/31 issue of the Journal of the American Medical Association.
For the study, Silber and his team compared nearly 7,400 black women, all aged 65 and older, who were diagnosed with breast cancer between 1991 and 2005. They followed them through 2009. All patients had Medicare insurance.
Silber compared the black women with breast cancer with three different groups of nearly 7,400 white women. One group was matched on demographics (age, year of diagnosis and geographic area). Another was matched on "presentation" (demographic variables plus tumor characteristics and coexisting health problems such as high blood pressure and heart failure). A third group was matched on treatment (the presentation variables plus information on surgery, radiation therapy and chemotherapy).
Silber found survival times were longer in whites, as other researchers have seen. "Whites live three years longer," he said.
When he looked at white women who had presentations similar to blacks, however, the story was different. "If the presentation is similar to blacks, they only live one year longer," he said.
Although nearly 69 percent of whites were alive at five years after diagnosis, less than 56 percent of black women were.
When Silber matched blacks and whites on presentation, the difference in five-year survival declined to 4.4 percent; when matched on treatment, it dropped to 3.6 percent.
These presentation factors explain most of the disparity, Silber said. "That includes differences in tumor stage and size, and higher rates of chronic health conditions such as diabetes and heart failure," he said.
"Treatment differences, though apparent, do not explain a large portion of the survival disparity," Silber said. "At this point, that is not driving the disparity."
Blacks were more likely not to have any treatment than whites and their time from diagnosis to treatment was longer -- 29 days compared to 22.
Even though the study uncovered some of the reasons for survival differences, the disparity can't yet be completely explained. "We don't fully understand why blacks present with worse disease characteristics," Silber said.
The study is important, said Dr. Jeanne Mandelblatt, a professor of oncology and medicine at the Georgetown Lombardi Comprehensive Cancer Center at Georgetown University Medical Center in Washington, D.C.
"I think the most important finding is they have quantified the importance of presentation versus treatment on the black-white disparity," Mandelblatt wrote in an editorial accompanying the study.
However, she cited some limitations. "[Silber] didn't consider a key component of breast cancer treatment -- hormonal treatment -- and more than two-thirds of older women get it," she said. Mandelblatt was referring to the five-year course of hormone therapy given after the initial treatment to lower the risk of death. The database also lacked some information about doses of chemotherapy, she said.
Dr. Laura Kruper, director of the Cooper-Finkel Women's Health Center and co-director of the breast oncology program at the City of Hope Cancer Center in Duarte, Calif., agreed that the lack of information about treatments is a limitation. But it's an understandable one, she said: "They can't compute all the treatment differences."
"In a statistically elegant way, they tried to parse out where the disparities in survival were," Kruper said. "Now we need out figure out why they are presenting later. It's not just screening. It's about access, and it's due to education and socioeconomic factors."
To learn more about survival differences in black and white women diagnosed with breast cancer, visit the American Cancer Society.