• Foluso O Ademuyiwa, Yu Tao, Jingqin Luo, Katherine Weilbaecher, and Cynthia X Ma.
• Division of Oncology, Department of Medicine, Washington University in St. Louis School of Medicine, St. Louis, MO, 63110, USA. bisiademuyiwa@wustl.edu.
• Breast Cancer Res. Treat. 2017 Feb 1; 161 (3): 491-499.

BackgroundTriple-negative breast cancer (TNBC) occurs at higher frequency in African Americans compared with Caucasians. It is unclear if the biology of TNBC is different in African American versus Caucasians. In this study, we sought to evaluate racial differences in the molecular pathology of TNBC.MethodsUsing data from The Cancer Genome Atlas, we identified TNBC patients with information on race. We analyzed differences in clinical characteristics, tumor somatic mutations, and gene expression patterns by race from whole exome and microarray data.Results1104 patients were identified, of which 178 had TNBC. TNBC was more frequent in African Americans than Caucasians (33.3 vs 14.9%). Although more African Americans than Caucasians overall were classified as basal-like from PAM50 gene expression (34.8 vs 16.1%), no differences in the TNBC cohort were observed. Median tumor somatic mutation counts were higher in African Americans versus Caucasians (39.5 vs 34), but no racial differences in the mutation counts in TNBC were observed. Somatic mutation analysis revealed racial differences in specific high prevalence genes in all patients (TP53 46% in African Americans vs 27% in Caucasians; PIK3CA 23% in African Americans vs 34% in Caucasians; and MLL3 12% in African Americans vs 6% in Caucasians). TNBC patients did not have any specific high prevalence genes associated with racial differences. There were no racial differences in gene expression patterns in selected genes involved in breast cancer biology. Overall, African Americans had shorter TTP and worse DFS. Racial differences in clinical outcomes were not observed in TNBC.ConclusionThe mutational landscape of TNBC is similar between African Americans and Caucasians. The higher frequency of TNBC in African Americans is therefore not associated with a different genomic profile of commonly established tumor regulatory pathway genes. Other modifiable factors may exist that contribute to the racial disparity in TNBC.

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