Tumours of germline BRCA mutation carriers lack wild-type functional copies of BRCA1 or BRCA2, but normal tissues retain a single wild-type copy of the relevant gene [73], making treatment with PARP inhibitors highly tumour-specific, and less toxic [86], as the tumours in BRCA-mutated patients are defective in homologous recombination [87]. This evidence concerns the gene BRCA2 and neoplasm.