This review summarises the researchbehind this development; charting the discovery of the first PARP enzyme (Chambon et al, 1963) and the development of PARPinhibitors as a class; highlighting why cancers defective in DNA repair could beselectively sensitive to these agents, and why the approval of the PARP inhibitorolaparib (Lynparza) has changed the management of BRCAm ovarian cancer. This evidence concerns the gene PARP1 and cancer.