BRCA2 and breast cancer: Similarly, BRCA1- and BRCA2-deficient breast cancers from TCGA had 0.31 and 0.33 median proportion of signature 3 compared to median of 0 in BRCA-proficient breast cancers (P = 3.5 x 10−20 and 3.4 x 10−18, respectively; Fig 1B).