MLH1 and head and neck squamous cell carcinoma: This prospective study aimed to investigate whether MLH1 c.-93G>A (rs1800734), MSH2 c.211+9C>G (rs2303426), MSH3 c.3133G>A (rs26279), EXO1 c.1765G>A (rs1047840), and EXO1 c.2270C>T (rs9350) single nucleotide polymorphisms (SNPs) of the mismatch repair (MMR) pathway change side effects and response rate of 90 HNSCC patients treated with CDDP and RT.