The potent survival benefit conferred by PARPi treatments in mice implanted with Brca1−/−Trp53−/− mammary tumors was completely lost when tumours were additionally deleted of 53bp1 (ref. 55); however, they modestly extended lifespan in equivalent tumor engraftment experiments when the tumors were instead deleted for Shld1 or Shld2 (ref. 22). Here, SHLD2 is linked to breast cancer.