PARP1 and cancer: Because of these somewhat opposing observations, that polymorphisms associated with reduced PARP-1 activity are associated with cancer predisposition on the one hand, and increased PARP activity in tumours on the other, we set out to investigate PARP-1 polymorphisms, expression and activity, using assays validated to GCLP for clinical trials, in a panel of 19 human cancer cell lines and one human immortalised cell line.