CDKN2A and head and neck squamous cell carcinoma: Indeed, in order to prove an ethiological involvement of HPV in a certain cancer development, e.g. in HNSCC, recently a very elaborate and strict methodological process has been described involving (i) control for carryover by HPV free tissue sections between experimental blocks, (ii) measurement of HPV oncogene expression by detection of E6 and/or E7 mRNA, and (iii) detection p16ink4a upregulation [65].