BRCA2 and breast cancer: Signature 3 is characterized by large insertions and deletions at breakpoint junctions and is strongly associated with germline mutations in BRCA1 and BRCA2. Because patients showing signature 3 are highly responsive to platinum-based chemotherapy, it is believed that their HR repair is defective31,32 However, a study conducted by Nik-Zainal et al. on TCGA data from 560 patients with BC revealed that 50% of the patients showing a signature 3 pattern had BRCA mutations, whereas the remaining 50% had dysfunctional BRCA-related DNA repair, despite the absence of BRCA mutations19.