BRCA1 and cancer: However, when both BRCA1 and 53BP1 are lost, repair by homologous recombination is restored and the sensitivity to DNA damaging agents is reduced, leading to resistance to cis-platinum and PARPi in BRCA1-deficient cells, suggesting a critical role of 53BP1 in cancer cells in which BRCA1 is mutated or epigenetically silenced [30-33].