Several differences between black and white women in the genotypic traits of their breast tumors have been identified and may explain, at least in part, the greater aggressiveness of breast cancer in black women, according to a report published online Sept. 14 in Journal of Clinical Oncology.

Researchers analyzed data from The Cancer Genome Atlas in what they described as the first study to systematically characterize the racial pattern of genomic and gene expression traits in primary breast tumors and to examine the association of these traits with tumor recurrence. They focused on 1,374 samples from white and 264 samples from black patients with stage I, II, or III breast cancer diagnosed in 1988-2013, reported Dr. Tanya Keenan of Massachusetts General Hospital and Harvard Medical School, Boston, and her associates.

The five most frequent mutations—in the TP53, PIK3CA, CDH1, GATA3, MLLT3, and MAP3K1 genes – were the same between black women and white women, but they occurred in different frequencies by race. Compared with white women, black women had significantly more TP53 mutations, more PAM50 basal tumors, and more TNBC basal-like 1 and mesenchymal stem–like tumors, all of which signal a more aggressive tumor biology. These differences also “might have implications as genotype-driven targeted therapies are developed,” the investigators said.

In addition, the breast cancers in black women had significantly greater intratumor genetic heterogeneity, which “may reflect either greater underlying genomic instability or more exposure to epigenetic or environmental agents of DNA damage. Either way, the greater genomic diversity within African American tumors suggests a greater capacity for clonal evolution that may contribute to aggressive or therapy-resistant disease,” they noted (J Clin Oncol. 2015 Sep 14. doi: 10.1200/JCO.2015.62.2126 ).

Black women had a higher risk of breast cancer recurrence than white women, which was greatly attenuated in multivariable analyses that controlled for their excess of TP53 mutations and PAM50 basal subtypes. This also suggests that differences in tumor genetics account, at least in part, for the known disparity in survival outcomes between the races, Dr. Keenan and her associates said.


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