BRCA2 and breast cancer: BRCA1- and BRCA2-deficient breast cancers had significantly higher number of reported mutations with the median number of mutations in WSI BRCA1- and BRCA2-deficient breast cancers being 2.4 and 2.6 fold higher, respectively, compared to BRCA-proficient breast cancers (P = 1.1 x 10−12 and 6.4 x 10−8, respectively; Fig 1C).