The BRCA1/2 pathogenic variant is germline in these patients, so both normal ovarian cells and breast cancer cells exhibit a deficiency in the DNA DSB repair machinery (although the extent of the deficiency likely differs: heterozygous in normal ovarian cells and likely homozygous in breast cancer cells due to a second genetic event, as suggested by Knudson’s hypothesis). This evidence concerns the gene BRCA1 and breast cancer.