RELIABILITY OF P16 IMMUNOHISTOCHEMISTRY IN THE DISCRIMINATION OF HPV-POSITIVE OROPHARYNGEAL SQUAMOUS CELL CARCINOMA

OBJECTIVE. Human Papillomavirus (HPV)-related squamous cell carcinoma of the oropharynx (HPV-OPSCC) usually originates from the reticulated epithelium lining the crypts of Waldeyer’s ring. The increasing epidemiologic evidence of this type of tumors and the peculiar positive prognosis, suggested to introduce a dedicated staging system (1). The 8th edition of the American Joint Committe on Cancer (AJCC) staging manual presented a new classification to discriminate HPV-related cancers based on p16 over-expression, since it demonstrated to be an important biomarker (2). The detection of HPV-DNA could not be used as a defining factor due to its cost and lack of universal applicability. The main purpose of this preliminary study was to evaluate the concordance between the results of immunohistochemistry for p16 overexpression and the HPV-DNA detection performed with a commercial kit as control. MATERIALS AND METHODS. We retrospectively collected 32 cases of OPSCC diagnosed in 2016 at the Academic Hospital of Cattinara in Trieste, whose samples had been tested with Real Time PCR (Pyro Mark System Q96 IDTM - CE-IVD Diatech Pharmacogentetics Iesi Italy). The study was performed using tumor samples fixed in buffered formalin, embedded in paraffin and stored at room temperature for 6 to 18 months. All samples were selected by a pathologist based on sections stained with hematoxylin and eosin to confirm the adequacy of the tissue. The samples were tested for p16 by immunohistochemistry (CINtech® p16 Histology E6H4 ROCHE) and the positivity was assessed when nuclear expression was ≥+2/+3 intensity and ≥75% distribution according to the 8th edition of the AJCC staging manual. In the context of oropharyngeal cancer, the optimal cut-off for p16 overexpression is ≥+2/+3 intensity (+/- cytoplasmic staining) with ≥75% distribution. RESULTS. Seven cases were excluded because of lack of histological stored material for p16 immunohistochemical analysis (only cytological specimen). Among the remaining 25 cases, there were 5 HPV-positive and 20 HPV-negative tumors. The sensibility and specificity of the p16 immunostaining was equal to 100% (95%, confidence interval 83.4%-100%) and 100% (95%, confidence interval 83.4%-97.8%), respectively; the positive predictive value was 100% (95%, confidence interval 83.4%-100%) and the negative predictive value 100% (95% confidence interval, 83.4%-100%). CONCLUSIONS. In agreement with the literature, p16 overexpression demonstrated to be a reliable parameter to identify the cases of OPSCC in which performing an in-depth analysis by means the detection of HPV-DNA would be indicated. Indeed, it is widely known that the association of p16 immunostaining and HPV-DNA detection by quantitative PCR increases the prognostic discriminator (3). We intend to carry on this study adopting a prospective design increasing the sample size and the test accuracy.