PARP1 and neoplasm: The observation that tumour cells exposed to chronic hypoxia acquire defects in homologous recombination and increased sensitivity to PARP inhibition (Hegan et al, 2010) is an example of ‘contextual synthetic lethality’ in which hypoxia-induced repair-deficient tumour cells can be targeted by disrupting backup pathways (Chan and Bristow, 2010).