GSTM1 and head and neck squamous cell carcinoma: EFS and OS of HNSCC patients with GSTM1 plus XPC c.2815A>C, GSTM1 plus XPD c.934G>A, GSTM1 plus XPD c.225A>C, and GSTM1 plus TP53 c.215G>C are presented in Fig. 1.