BRCA1 and neoplasm: Moreover, ionizing radiation (IR)-induced RAD51 foci assemble in olaparib-resistant Brca1−/−, 53BP1-deficient cells (albeit not at the same level as in Brca1+/+ cells), but not in olaparib-sensitive Brca1−/− tumor-derived cells (Jaspers et al., 2013).