Within-stage racial differences in tumor size and number of positive lymph nodes in women with breast cancer

BACKGROUND. Black women have higher breast cancer mortality rates, are more likely to be diagnosed at an advanced stage of disease, and have worse stage-forstage survival than white women. It was hypothesized that differences in the tumor size and number of positive lymph nodes within each disease stage contribute to the survival disparity. METHODS. in the National Cancer Institute's Surveillance, Epidemiology, and End Results (SEER) database, black and white women diagnosed with a first primary tumor (TNM stage I-IIIA breast cancer) between 1988 and 2003 were identified. The demographic and clinical characteristics were compared by race. Logistic regression models of the association between race and tumor size and lymph node status were developed. Cox proportional hazards models of the association between mortality and race, tumor size, lymph node status, and other covariates were also examined. RESULTS. Among 256,174 SEER cases (21,861 black and 234,313 white women), more black than white women with lymph node-negative breast cancer had tumors measuring >= 2.0 cm. Adjusted for tumor size, more black than white women had >= 1 positive lymph nodes (odds ratio [OR], 1.24; 95% confidence interval [95% CI], 1.20-1.28). The age-adjusted and TNM stage-adjusted mortality rate ratio for blacks versus whites was 1.56 (95% CI, 1.51-1.61). Adjustment for within-stage differences in tumor size and lymph node involvement were found to have a negligible effect. With adjustment for additional covariates, the rate ratio was 1.39 (95% CI, 1.35-1.44). In addition, the rate ratio reflecting racial disparity increased as the stage of disease increased. CONCLUSIONS. Adjusting for within-stage differences in tumor size and lymph node status did not appear to reduce the racial disparity. The finding that disparities increased with higher stage of disease suggests that interventions aimed at reducing these differences should target women with more advanced disease.