The identification of Human Papilloma Virus (HPV) is very useful to identify a subset of head and neck cancer, especially oropharyngeal, with peculiar biological characteristics and favorable prognosis. In this setting it is important to have a sensitive and reliable method to identify high-risk (HR)-HPV types in formalin fixed-paraffin embedded (FFPE) specimens. We sought to define the optimal technical approach to identify HPV-related head and neck carcinomas, in order to reach adequate sensitivity and specificity with a method applicable to diagnostic laboratory routine. In addition, we wanted to evaluate if HR-HPV could be involved in non-oropharyngeal head and neck cancers.
We analyzed a total of 101 FFPE oropharyngeal squamous cell carcinomas (SCC), diagnosed from 1998 to 2015 in our institution and for comparison 43 non-oropharyngeal SCC (31 of the oral cavity, 6 of the larynx and 6 from other head and neck sites). All the samples were tested with HR-HPV In Situ Hybridization (ISH) Kit (Roche) and p16 Immunohistochemistry (IHC) (CINtec Histology v-kit Roche). On a subset of 34 oropharyngeal SCC we also performed the cartridge-based GeneXpert HPV assay (Cepheid), a qualitative real time PCR assay validated to detect HR-HPV DNA in cervical cytological specimens.
With ISH analysis, we identified HR-HPV positive cases in 32/101 (32%) oropharyngeal SCC and in 0/31 SCC of the oral cavity. In addition, we identified two HR-HPV positive SCC, one in the larynx and one in the nasal cavity. We obtained a good correlation between p16 and ISH, given that 118 of 133 comparable cases (89%) gave concordant results. The discordant cases included 12 out of 133 cases (9%) that were p16+/ISH- and 3 cases that were p16-/ISH+ (2%). In the cases studied with PCR, we obtained valid results in 28/34 cases (82%), with a 86% concordance with ISH analysis (24/28 cases). Three of 4 discordant cases were ISH-/PCR+ with a strong p16 immunoreactivity, evidencing a slightly better sensitivity of PCR in HPV detection. The latter discordant case was ISH+/PCR-, and showed no p16 immunoreactivity. Interestingly, the viral type identified was type 16 in 17/19 PCR positive cases.
The optimal strategy for the accurate identification of HR-HPV positive head and neck carcinomas is to combine the sensitivity of p16 IHC analysis and the specificity of ISH or PCR analysis. PCR showed a slightly greater sensitivity for HPV identification compared to ISH analysis: notably, GeneXpert HPV assay showed a good efficiency also starting from FFPE material. The impact of HPV in non-oropharyngeal head and neck SCC seems to be very limited in our series.