The incidence of mutations that restore BRCA1/2 function in ovarian cancer ranges from 0% to 21%, and as high as 40% to 50% in breast cancer.62, 63, 64 A pooled analysis of several studies on reversion mutations revealed mutagenic end-joining DNA repair pathways, particularly those affecting BRCA2, play a key role in the generation of reversion, as indicated by a significant accumulation of microhomology in deletions surrounding DNA sequences leading to reversion events.65 The gene discussed is BRCA1; the disease is ovarian carcinoma.