PARP1 and neoplasm: In tumors with biallelic BRCA1/2 inactivation, homologous recombination (HR) is impaired; pharmacologic PARP inhibition disables PARP-mediated single-strand break/base-excision repair and promotes PARP trapping on DNA, leading to replication-fork collapse, accumulation of lethal DNA damage, and selective tumor-cell death in HRD tumors (25).