ERCC4 and head and neck squamous cell carcinoma: It is possible that the sum or synergism of functional abnormalities, such as detoxification and apoptosis, as seen in GSTM1 present plus TP53 c.215GC or CC combined genotype, and repair double defect, as seen in XPD c.2251AA plus XPF c.2505TT is necessary to alter the survival of HNSCC cells and HNSCC patients ́ survival in the current analysis, and this the most plausible explanation for the association of combined genotypes but not of isolated genotypes with the survival of patients enrolled in the recent analysis of this prospective study.