MPO and nasopharyngeal carcinoma: We also investigated sixteen adjacent tagging SNPs of GSTP1, MPO and NQO1 (which covered 100% haplotype variation within these genes), and four SNPs of CYP2E1 (one of which covered CYP2E1-RsaI polymorphisms) in another independent case-control cohort with 213 NPC cases and 230 controls.