Tumor-infiltrating lymphocytes and breast cancer mortality in racially and ethnically diverse participants of the Northern California Breast Cancer Family Registry.

Stromal tumor-infiltrating lymphocyte (sTIL) enrichment in pretreatment breast tumors has been associated with superior response to neoadjuvant treatment and survival. In a population-based cohort, we studied sTIL-survival associations by race and ethnicity. We assessed associations of continuous sTIL scores and sTIL-enriched breast cancers (defined as percent lymphocytic infiltration of tumor stroma or cell nests at cutoffs of 30%, 50%, and 70%) with clinical and epidemiologic characteristics and conducted multivariable survival analyses. Although we identified no difference in sTIL score by race and ethnicity, higher continuous sTIL score was associated with lower breast cancer-specific mortality only among non-Hispanic White and Asian American but not African American and Hispanic women. This finding suggests that complex factors influence treatment response and survival, given that sTIL enrichment was not associated with a survival advantage among women from minoritized groups, who more often experience health disparities. Further study of patient selection for sTIL-guided treatment strategies is warranted.