Oropharyngeal squamous cell carcinoma: p16/p53 immunohistochemistry as a strong predictor of HPV tumour status.

Abstract

Oropharyngeal squamous cell carcinomas (OPSCC) related to human papillomavirus (HPV) infection have a better prognosis than those without HPV infection. Although p16INK4a overexpression is used as a surrogate marker for HPV infection, 5-20% of p16-positive OPSCC are described as being unrelated to HPV infection, with worse overall survival compared to OPSCC-related HPV. There is therefore a risk of undertreating a proportion of OPSCC patients falsely considered to be HPV-driven because of p16 positivity. TP53 mutations are highly prevalent in OPSCC driven by mutagens in tobacco and alcohol. We describe herein a combined p16/p53 algorithm to predict HPV tumour status in OPSCC. A total of 110 OPSCC were identified in the database of the pathology department and were studied using p16 and p53 immunohistochemistry. For p16-positive or p16-negative/wild-type patterns-p53 (WT-p53) cases (n=63), DNA in-situ hybridisation for high-risk HPV was performed, and if negative the HPV status was controlled by HPV DNA polymerase chain reaction (PCR) (n=19). A significant association between TP53 mutation and pattern of p53 expression was found (WT-p53, seven of 16, P<0.001). The p16-positive/WT-p53 was significantly associated with HPV+ tumour status (p16-positive/WT-p53, 50 of 110, P<0.001). Interestingly, a subset of p16-positive OPSCC was unrelated to HPV (13.5%, eight of 59), and showed mutant-type staining of p53 expression. The p16 protein immunopositivity in conjunction with the mutant-type pattern of p53 staining helped to reclassify a subset of p16-positive OPSCC as OPSCC-unrelated HPV. This approach could be routinely applied by pathologists involved in the management of OPSCC, because of their potential therapeutic implications.