Racial Disparities in Survival in Breast Cancer

Healthcare researchers have identified racial disparities in survival among women with breast cancer for the past 20 years. Studies have demonstrated worse outcomes in black patients with breast cancer and have identified possible reasons for the disparities, including differences in screening, presentation, comorbid conditions on presentation, tumor biology, stage, treatment, and socioeconomic status.

Researchers recently conducted a study to identify the extent of racial disparity in survival among patients with breast cancer in the Medicare population. The primary goal of the study was to determine if the disparity is primarily attributable to differences in presentation characteristic at diagnosis or to differences in subsequent treatment. Results were reported in JAMA [2013;310(4):389-397].

The study was also designed to assess the magnitude of the disparity, whether the disparity changed between the era before introduction of taxanes (1991-1998) and the era after the introduction of taxanes (1999-2005), the relative contributions of presentation at diagnosis and treatment after diagnosis to differences in survival, and the effect of socioeconomic status on the survival differences.

The researchers compared the entire population of black women in the Surveillance, Epidemiology and End Results (SEER)-Medicare database with 3 white female populations individually paired to the black population to answer (1) are white women who present like black women treated in the same way as black patients, and, if not, (2) to what extent does a difference in treatment explain the disparity in survival?

The study cohort included 7375 black women ≥65 years of age diagnosed with breast cancer between 1991 to 2005 and 3 sets of 7375 matched white women (controls), selected from 99,989 white potential controls. All participants received follow-up through December 31, 2009. The black women were matched to the white controls on demographics (age, year of diagnosis, SEER site), presentation (demographics variables plus patient comorbid conditions and tumor characteristics), and treatment (presentation variables plus details of surgery, radiation therapy, and chemotherapy).

In the demographics match, 5-year survival among black women was 55.9%, compared with 68.8% among the white female participants (absolute difference, 12.9%; 95% confidence interval [CI], 11.5%-14.5%; P<.001). The difference was unchanged between 1991 and 2005.

Following matching based in presentation characteristics, the absolute difference in 5-year survival was 4.4% (95% CI, 2.8%-5.8%; P<.001). The absolute difference in 5-year survival between the treatment-matched white female population and the total black female population was 3.6% (P<.001).

In the presentation match, fewer black women received treatment compared with white women (87.4% vs 91.8%: P<.001), time from diagnosis to treatment was longer (29.2 days vs 22.8 days; P<.001), use of anthracyclines and taxols was lower (3.7% vs 5.0%; P<.001), and breast-conserving surgery without other treatment was more frequent (8.2% vs 7.3%; P=.04). However, the researchers noted, differences in survival associated with treatment differences accounted for only 0.81% of the 12.9% survival difference.

Limitations to the study cited by the researchers included the lack of chart review to verify definitions of treatment coded from Medicare bills or noted in SEER data, which prevented the tracking of the use of tamoxifen. In addition, use of SEER data did not allow the researchers to define triple-negative tumors; however, the researchers noted that triple-negative tumors are less common in postmenopausal than premenopausal black women (14% vs 39%), and postmenopausal black and white women display no difference in their rates of triple-negative tumors.

In conclusion, the researchers stated, “In the SEER-Medicare database, differences in breast cancer survival between black and white women did not substantially change among women diagnosed between 1991 and 2005. These differences in survival appear primarily related to presentation characteristics at diagnosis rather than treatment differences.”