The precise mechanistic details responsible for defective DSB repair are still unclear as both reduced protein expression of 53BP1 and DNA-Pk involved in NHEJ, and BRCA2 and RAD51 involved in HR have been shown in two HPV-positive HNSCC cells, but only in comparison to a single HPV-negative cell line [12]. This evidence concerns the gene PRKDC and head and neck squamous cell carcinoma.