Tumours harbouring a BRCA mutation or other defect in homologous recombination repair are sensitive to PARP inhibitors, because cells accumulate unrepaired single-strand breaks that are converted to double-strand breaks that cannot be repaired and therefore result in cell death (Bryant et al, 2005; Farmer et al, 2005; Helleday et al, 2007, 2008; Ashworth, 2008). The gene discussed is PARP1; the disease is neoplasm.