BRCA1 and cancer: However, there was no evidence of BRCA1 loss of heterozygosity (Fig. 1c) nor BRCA1/2 germline defects that would suggest biallelic inactivation of BRCA1. While we cannot rule out the possibility that the PARP inhibitor olaparib contributed to NCI0422’s CR, given BRCA1 mutations are rare in SCLC2 and SCLC is not a BRCA-associated cancer type20, it is unlikely to have accounted for the CR to the ICB combination.