Several epidemiologic investigations of genetic susceptibility to NPC have discovered SNPs in relation to genetic polymorphisms in cytochrome P450 (CYP) and glutathione-S-transferase (GST) gene families encode phase I and II xenobiotic metabolism enzymes involved in the biotransformation of chemicals such as the toxin of Cd (30–32). This evidence concerns the gene PPIG and nasopharyngeal carcinoma.