GAPDH and neoplasm: The mean expression, normalized against GAPDH, of MTH1, MTH2, MTH3 and NUDT5 in tumor tissues were 0.724±0.295, 0.478±0.435, 0.568±0.171 and 0.761±0.278 (mean±SD), respectively, which were significantly higher than the mean values of 0.077±0.052, 0.054±0.037, 0.147±0.109 and 0.191±0.096 for normal tissues, respectively.