Reappraisal of p16 for Determining HPV Status of Head and Neck Carcinomas Arising in HPV Hotspots

In an era of head and neck oncology where HPV status will soon dictate patient management, reliable HPV detection is critical. P16 immunohistochemistry (IHC) is currently recommended as the test of choice for oropharyngeal squamous cell carcinomas (OPSCCs). The purpose of this study was to determine the performance characteristics of p16 IHC based on a large clinical experience of squamous cell carcinomas (SCC) arising from HPV hot-spot regions of the head and neck. Consecutive OPSCCs, sinonasal SCCs, and metastatic SCCs of unknown primary sites were evaluated for the presence of HPV by p16 IHC and PCR-based HPV DNA testing as part of clinical care. For discrepant cases, high-risk HPV E6/E7 mRNA in situ hybridization (ISH) and, when possible, matrix-Assisted laser desorption/ionization-time of flight (MALDI-TOF) mass spectrometry (MassArray) genotyping were performed. 746 cancers underwent HPV testing by p16 IHC and DNA PCR genotyping. There was a 95.6% concordance between the 2 assays. Of the 33 discrepant cases, 32 cases (4.3%) were p16 positive but HPV DNA negative. In these cases, 68% were positive for mRNA ISH, invariably related to a non-16 HPV genotype. P16 IHC had an overall accuracy of 98.8%, a sensitivity of 99.8%, and a specificity of 92.1%. P16 IHC is a sensitive and specific assay for determining HPV status. HPV DNA PCR appears vulnerable to HPV genotype diversity and is prone to missing rare non-16 genotypes. HPV mRNA ISH is a practical and reliable direct measure of HPV that may help eliminate the small number of false-positive p16 cases and avoid potential patient harm related to erroneous HPV classification.