HPGDS and nasopharyngeal carcinoma: GSTM1 (glutathione S‐transferase M1) is a member of the family of cytosolic GSTs, and the null genotype of GSTM1 has been proven to be associated with risk of colorectal cancer, renal cell carcinoma, oesophageal cancer, nasopharyngeal cancer and bladder cancer.42, 43, 44, 45, 46