XRCC6P5 and neoplasm: Temozolomide and lomustine (CCNU) showed parallel toxicity in seven human tumour cell lines and this generally correlated (correlation coefficients 0.87 and 0.92 respectively) with the level of expression of the DNA repair protein O6-alkylguanine-DNA alkyltransferase (ATase, EC 2.1.1.63).