GSTP1 and head and neck cancer: Considering the evidence presented, this study aimed to investigate the association of GSTM1 and GSTT1 null genotypes and single nucleotide polymorphisms (SNPs) A313G and C341T of the GSTP1 gene with head and neck cancer, as well as to verify the association between these polymorphisms and the anatomical site of tumor occurrence, clinical-pathological characteristics, relapse-free time and survival of patients with head and neck cancer treated with chemotherapy and/or radiotherapy.