BackgroundEndocrine-resistant HR+/HER2- breast cancer (BC) and triple-negative BC (TNBC) are of interest for molecularly informed treatment due to their aggressive natures and limited treatment profiles. Patients of African Ancestry (AA) experience higher rates of TNBC and mortality than European Ancestry (EA) patients, despite lower overall BC incidence. Here, we compare the molecular landscapes of AA and EA patients with HR+/HER2- BC and TNBC in a real-world cohort to promote equity in precision oncology by illuminating the heterogeneity of potentially druggable genomic and transcriptomic pathways.MethodsDe-identified records from patients with TNBC or HR+/HER2- BC in the Tempus Database were randomly selected (N= 5000), with most having stage IV disease. Mutations, gene expression, and transcriptional signatures were evaluated from next-generation sequencing data. Genetic ancestry was estimated from DNA-seq. Differences in mutational prevalence, gene expression, and transcriptional signatures between AA and EA were compared. EA patients were used as the reference population for log fold-changes (logFC) in expression.ResultsAfter applying inclusion criteria, 3433 samples were evaluated (n= 623 AA andn= 2810 EA). Observed patterns of dysregulated pathways demonstrated significant heterogeneity among the two groups. Notably,PIK3CAmutations were significantly lower in AA HR+/HER2- tumors (AA = 34% vs. EA = 42%,P< 0.05) and the overall cohort (AA = 28% vs. EA = 37%,P= 2.08e−05). Conversely,KMT2Cmutation was significantly more frequent in AA than EA TNBC (23% vs. 12%,P< 0.05) and HR+/HER2- (24% vs. 15%,P= 3e−03) tumors. Across all subtypes and stages, over 8000 genes were differentially expressed between the two ancestral groups includingRPL10(logFC = 2.26, P= 1.70e−162),HSPA1A(logFC = − 2.73,P= 2.43e−49), ATRX(logFC = − 1.93,P= 5.89e−83),andNUTM2F(logFC = 2.28,P= 3.22e−196). Ten differentially expressed gene sets were identified among stage IV HR+/HER2- tumors, of which four were considered relevant to BC treatment and were significantly enriched in EA: ERBB2_UP.V1_UP (P= 3.95e−06), LTE2_UP.V1_UP (P= 2.90e−05), HALLMARK_FATTY_ACID_METABOLISM (P= 0.0073), and HALLMARK_ANDROGEN_RESPONSE (P= 0.0074).ConclusionsWe observed significant differences in mutational spectra, gene expression, and relevant transcriptional signatures between patients with genetically determined African and European ancestries, particularly within the HR+/HER2- BC and TNBC subtypes. These findings could guide future development of treatment strategies by providing opportunities for biomarker-informed research and, ultimately, clinical decisions for precision oncology care in diverse populations.Supplementary InformationThe online version contains supplementary material available at 10.1186/s13058-023-01627-2.