Despite progress in breast cancer treatment, disparity persists in survival time between African American (AA) and Caucasian women in the US. Tumor stage and tumor grade are the major prognostic factors that define tumor aggressiveness and contribute to racial disparity between AA and Caucasian women. Studying the interaction of race with tumor grade or stage may provide further insights into the role of intrinsic biological aggressiveness in disecting the AA-Caucasian survival disparity. Therefore, the current study was performed to evaluate the interaction of race with tumor grade and stage at diagnosis regarding survival in a cohort of patients treated at the Winthrop P. Rockefeller Cancer Institute of the University of Arkansas for Medical Sciences (Little Rock, AR, USA). The cohort included 1,077 patients, 208 (19.3%) AA and 869 (80.7%) Caucasian, diagnosed with breast cancer between January 1997 and December 2005. Kaplan-Meier survival plots were generated and Cox regressions were performed to analyze the associations of race with breast cancer-specific survival time. Over a mean follow-up time of 1.5 years, AA women displayed increased mortality risk due to breast cancer-specific causes [hazard ratio (HR), 1.74; 95% confidence interval (CI), 1.23-2.46]. The magnitude of racial disparity varied strongly with tumor grade (race-x-grade interaction; P<0.001). No significant interaction was observed between race and tumor stage or race and age at diagnosis. Among women diagnosed with grade I tumors, the race disparity in survival time after controlling for tumor stage and age was strong (HR, 9.07; 95% CI, 2.11-38.95), but no significant AA-Caucasian disparity was observed among women with higher-grade tumors. The data suggest that, when diagnosed with grade I breast cancer, AA may experience poorer survival outcomes compared with Caucasian patients, regardless of tumor stage or age. The findings potentially provide significant clinical and public health implications and justify further investigation.
Keywords: African American; Caucasian; breast cancer; health disparity.