Histomorphology based prediction of p16 immunopositivity and p16/HPV DNA co-positivity in oral squamous cell carcinoma

The histomorphological features predictive of p16 and human papilloma virus (HPV DNA) positivity in oropharyngeal carcinoma have been a matter of much debate. However, only few studies have been done on oral squamous cell carcinoma (OSCC) to correlate the histomorphological features with p16 and HPV DNA positivity. Oral squamous cell carcinoma has distinct etiopathogenesis, treatment and prognosis as compared to oropharyngeal carcinomas. A total of 800 oral squamous cell carcinoma biopsy cases were evaluated for features suggestive of HPV infection like basaloid appearance, absence of stromal reaction, nests and lobules of tumor cells with pushing borders, central necrosis, lympho-epithelial morphology, koilocytes, and non-keratinizing or hybrid morphology. Immunohistochemistry was performed for p16 expression (E6H4 clone, CINtec histology, Roche diagnostics). The cases which showed 2+/3+ (from moderate to high intensity) staining with >75 % cells were considered as p16 immunopositive. All the p16 immunopositive cases were subjected to real-time PCR (polymerase chain reaction) for HPV DNA detection to confirm HPV positivity. A total of 139 (17.37 %) OSCC cases were p16 immunopositive and out of these 104 (104/139, 74.8 %) cases showed HPV-DNA PCR positivity. None of the features were found to be predictive on multivariate logistic regression analysis. However, on bivariable analysis, nest/lobule with pushing border was the only histopathological feature which had a significant correlation with p16 immunopositivity (P value = 0.0001) and p16 and HPV DNA copositivity (P value = 0.0001). (Fisher's exact test -two tailed). To conclude-morphology is not really predictive of HPV positivity in OSCC cases. Only one feature- nests and lobule with pushing border is suggestive on bivariable analysis.