Strikingly, polygenic mutations in BRCA2 + RAD51C in breast tumors led to significantly more severe disease and reduced the overall survival by >90 months compared to patients with single BRCA2 or RAD51C mutations only (Figs. 5a, 3.2-fold decrease in median overall survival in breast cancer patients with polygenic compared to monogenic BRCA2 or RAD51C tumor mutations, 3.5-fold decrease in median survival in patients with polygenic tumor mutations compared to patients with no BRCA2 or RAD51C mutation). This evidence concerns the gene BRCA2 and breast cancer.