PARP1 and cancer: For instance, BRCA-deficient cancer cells, in which DNA double strand break repair (DSB) by homologous recombination is deficient [3,4], are particular sensitive to treatment with inhibitors of Poly(ADP-ribose) (PAR) polymerase 1 (PARP-1), a nuclear enzyme that recognizes and facilitates repair of DNA damage induced by oxidation, alkylation and ionizing radiation [2,5-7], showing reduced clonogenic survival and DNA DSB repair defects [8,9].