HPRT1 and neoplasm: This effect may be related to the HPRT mutagenesis seen in BRCA2 mutant Capan-1 cells.12 If PARP inhibition has a weak selective mutagenic effect on BRCA1/2-deficient cells only, this may accelerate the development of resistance in existing BRCA-deficient tumours, but would not contribute to the induction of secondary malignancies.