BRCA1 and cancer: PARP1,2 inhibition is selectively lethal in cancer with mutation in the BRCA1,2 tumour suppressors, causing HRd22, and multiple PARPi have regulator approval for the treatment of HRd and/or BRCA1,2-mutated ovarian, breast and pancreatic cancers, with recent FDA breakthrough status in castration-resistant prostate cancer23,24.