Population-specific patterns in assessing molecular subtypes of young black females with triple-negative breast...

We determined triple-negative breast cancer (TNBC) subtypes, genetic ancestry, and immune features in a cohort of self-reported Black females with TNBC diagnosed at or below age 50. Among 104 tumors, 34.6% were basal-like 1 (BL1), 17.3% basal-like 2 (BL2), 9.6% luminal androgen receptor (LAR), 26.9% mesenchymal (M), and 11.5% unsubtyped (UNS). Subtypes resembled those seen in Europeans or East Asians, with less LAR (9.6% vs. 14.6-24.4%) and more UNS (11.5% vs. 0-7.5%). "High" proportion of West African ancestry was associated with more LAR (14.9% vs. 4.9%) and less M (25.5% vs. 34.2%). M demonstrated reduced immune activity and was marginally associated with worse overall survival in a multivariate model including stage, West African ancestry, BMI, and TILs, meriting future research. Our study is the largest to date of TNBC subtypes in young Black females. These results reinforce TNBC subtypes' application across populations and potential use as a prognostic biomarker.