p16 INK4A overexpression is frequently detected in tumour-free tonsil tissue without association with HPV.

AIMS: Oncogenic human papillomavirus (HPV) type 16 has been strongly associated with tonsillar squamous cell carcinoma (TSCC) and appears to be of prognostic significance. Because HPV+ TSCC also accumulates p16(INK4A), this cyclin-dependent kinase inhibitor has been proposed as a potential biomarker for HPV in clinical diagnosis. The aim of this study was to determine the prevalence of HPV in tumour-free tonsillar tissue and the value of p16(INK4A) overexpression in predicting its presence.

METHODS AND RESULTS: p16(INK4A) overexpression was detected by immunohistochemistry in tissue sections of tumour-free tonsils of 262 patients. They were treated for non-oncological reasons (snoring or chronic/recurrent tonsillitis) consisting of tonsillectomy. Genomic DNA isolated from these tissues was subjected to HPV-specific polymerase chain reaction (PCR) analysis. p16(INK4A) immunoreactivity was detected in 28% of samples in both crypt epithelium (49/177) and lymphoid germinal centres (52/187), which correlated with each other (P < 0.0001). No reactivity was observed in superficial squamous cell epithelium. HPV16 and 18 were detected by PCR analysis in 2/195 cases (1%), which, however, were negative on fluorescence in situ hybridization analysis and discrepant on p16(INK4A) immunostaining.

CONCLUSIONS: No proof was found for the presence of HPV in tumour-free tonsil tissue, despite increased p16(INK4A) expression in a quarter of tonsil cases. Other mechanisms than HPV infection are therefore implicated in p16(INK4A) up-regulation.