BRCA1 and neoplasm: To test the potential of PDS to eliminate Brca1-deficient mouse tumor-derived cells refractory to olaparib, we used two Brca1−/− cellular mouse models, in which olaparib resistance was mediated by concomitant loss of REV7 (Figure 7A; Xu et al., 2015) or 53BP1 (Figure 7B; Jaspers et al., 2013).