Racial differences in CD8⁺ T cell infiltration in breast tumors from Black and White women

African American/Black women with breast cancer have poorer survival than White women, and this disparity persists even after adjusting for non-biological factors. Differences in tumor immune biology have been reported between Black and White women, and the tumor immune milieu could potentially drive racial differences in breast cancer etiology and outcome.

We examined the association of CD8⁺ cytotoxic T cells with clinical-pathological variables in the Women's Circle of Health Study (WCHS) population of predominantly Black breast cancer patients. We evaluated 688 invasive breast tumor samples (550 Black, 138 White) using immunohistochemical staining of tissue microarray slides. CD8⁺ T cells were scored for each patient tumor sample with digital image analysis.

Black women had a significantly higher percentage of high-grade, estrogen receptor (ER)-negative, and triple-negative tumors than White women and significantly higher CD8⁺ T cell density (median 87.6/mm² vs. 53.1/mm²; p < 0.001). Within the overall population and in the population of Black women only, CD8⁺ T cell density was significantly higher in younger patients and patients with high-grade and ER/PR-negative tumors. No significant associations were observed between CD8⁺ T cell density and overall survival or breast cancer-specific survival in the overall population, or when Black patients were analyzed as a separate group. However, when stratified by subtype, Black women with triple-negative breast cancer and high CD8⁺ T cell density showed a trend towards better overall survival in comparison with patients with low CD8⁺ T cell density (HR = 0.51; 95% CI 0.25-1.04).

Our data raise the possibility that distinct mechanisms of immune cell action may occur in different racial groups.