BRCA1 and neoplasm: Tumour cells that lack BRCA1 or BRCA2 are deficient in error-free homologous recombination (HR), and DNA double-stranded breaks (DSBs) accumulated during DNA replication need to be repaired by alternative, error-prone repair pathways, which results in incorrect repair of the DNA lesions caused by PARPi and consequent cytotoxicity [8].