HPV DNA, E6*I-mRNA expression and p16INK4A immunohistochemistry in head and neck cancer – How valid is p16INK4A as surrogate marker?

It has been proposed that p16INK4A qualifies as a surrogate marker for viral oncogene activity in head and neck cancer (HNSCC). By analyzing 78 HNSCC we sought to validate the accuracy of p16INK4A as a reliable marker of active HPV infections in HNSCC. To this end we determined HPV DNA (HPVD) and E6*I mRNA (HPVR) expression status and correlated these results with p16INK4A staining. In tonsillar SCC 12/20 were HPVD+ and 12/12 of these showed active HPV infections whereas in non-tonsillar SCC 10/58 were HPVD+ and 5/10 showed active HPV infections. Thus, we prove about 8% of non-tonsillar SCC to be also correlated with HPV-associated carcinogenesis. Strikingly, 3/14 (21.4%) of tonsillar and non-tonsillar HPVD+/HPVR+ cases did not show p16INK4A overexpression and these cases would have been missed when applying initial p16INK4A staining only. However, in 13 cases negative for HPV, DNA p16INK4A was overexpressed. In conclusion, our data confirm tonsillar SCC to be predominantly but not only associated with active HPV infections. Furthermore, our data show that p16INK4A overexpression is not evident in a subgroup of HNSCC with active HPV infection. Definitive HPV data should therefore be utilized in diagnostics and treatment modalities of HPV positive and HPV negative HNSCC patients, resulting in a paradigm shift regarding these obviously different tumor entities.