GSTM1 and hepatocellular carcinoma: In a combined analysis, significantly increased HCC risks were found for null genotype of GSTM1 (OR = 1.29, 95% CI: 1.06–1.58; P = 0.01) and GSTT1 (OR = 1.43, 95% CI: 1.22–1.68; P<10−5).