BRCA1 and neoplasm: The wild-type BRCA allele commonly undergoes loss-of-heterozygosity during tumourigenesis in individuals with heterozygous BRCA1/2 m, leading to severe deficiency in the homologous recombination pathway.20 Therefore, a germline heterozygous BRCA1/2 mutation may be sufficient to identify tumour cells that are more likely to be sensitive to PARPi.