BRCA1 and breast cancer: In addition, the PARP inhibitor olaparib has limited effects on breast cancer patients harboring germline mutations of BRCA1, especially the mutant with increased expression of BRCA1 exon 11 skipping (BRCA1-Δ11q) (Wang et al., 2016; Kim et al., 2017; Paschalis et al., 2018; Siegfried and Karni, 2018).