BRCA1 and neoplasm: This suggests that PARP1 trapping still underlies the increased cytotoxicity of PARPi in these tumour cells but that some residual BRCA1 function allows these cells to tolerate PARP1 mutations (Fig. 3f–h), consistent with previous observations that some BRCA1 exon 11 mutations do not result in complete loss of BRCA1 function24, 25.