Discrepancy of p16 immunohistochemical expression and HPV RNA in penile cancer. A multiplex in situ hybridization/immunohistochemistry approach study

BACKGROUND: The high-risk human papillomavirus (HPV) infection represents one of the main etiologic pathways of penile carcinogenesis in approximately 30-50% of cases. Several techniques for the detection of HPV are currently available including Polymerase chain reaction-based techniques, DNA and RNA in situ hybridization (ISH), p16 immunohistochemistry (IHC). The multiplex HPV RNA ISH/p16 IHC is a novel technique for the simultaneous detection of HPV E6/E7 transcripts and p16INK4a overexpression on the same slide in a single assay. The main aim of this study was to evaluate the discrepancy of p16 IHC expression relatively to HPV RNA ISH in penile cancer tissue.METHODS: We collected a series of 60 PCs. HPV has been analysed through the RNA ISH, p16 IHC and the multiplex HPV RNA ISH/p16 IHC.RESULTS: The multiplex HPV RNA ISH /p16 IHC results in the series were in complete agreement with the previous results obtained through the classic p16 IHC and HPV RNA scope carried out on two different slides. The multiplex HPV RNA ISH /p16 IHC showed that HPV positivity in our series is more frequently in usual squamous cell carcinoma than in special histotypes (19 out of 60-15%- versus 6 out of 60-10%-), in high-grade than in moderate/low grade carcinomas (6 out of 60-10%- versus 4 out of 60-6.7%-). In addition, our data revealed that in 5 out of 20 cases with p16 high intensity expression is not associated with HPV RNA ISH positivity.CONCLUSIONS: Our findings emphasize that the use of p16 as a surrogate of HPV positivity was unsuccessful in approximatively 8% of cases analysed in our series. Indeed, p16 IHC showed a sensitivity of 100% and a specificity of 71%, with a positive predictive value (PPV) of 54% and a negative predictive value of 100%; when considering high intensity, p16 IHC showed a sensitivity of 100%, a specificity of 89%, with a PPV of 75% and NPV of 100%. Since HPV positivity could represent a relevant prognostic and predictive value, the correct characterization offered by this approach appears to be of paramount importance.