Shinn JR, Davis SJ, Lang-Kuhs KA, et al. - In previous studies, 5% to 10% of oropharyngeal squamous cell carcinomas are identified as overexpressing p16 but with no association with transcriptionally-active high-risk human papillomavirus (HPV). Researchers herein performed a multi-institutional, retrospective review of oropharyngeal squamous cell carcinoma patients with p16 IHC and HPV mRNA testing by reverse transcriptase polymerase chain reaction in order to report the rate of p16 and HPV mRNA positivity, characterize patients with discordant testing, and determine features that may warrant selective use of HPV-specific testing after p16 IHC. Among 467 assessed patients, 71% had T1 or T2 tumors, 82% were p16 positive, and 84% were HPV mRNA positive. Overall, most tumors were nonkeratinizing (378, 81%), which was strongly associated with p16 and HPV positivity (93% and 95%, respectively). Overall, 81% of patients were reported as double positive, 14% were reported double negative, and 4.9% were reported as discordant (3.4% p16 negative/HPV mRNA positive and 1.5% p16 positive/HPV mRNA negative). The survival rates of these discordant patient groups fell squarely between the 2 concordant groups, although multivariate analysis for both disease-free survival and overall survival did not suggest statistically significantly different outcomes for discordant patients. Reclassification of patients by applying HPV mRNA testing when p16 results and morphology do not match, or when p16 results are equivocal, led to slight improvement in prognostication over p16 or HPV mRNA testing alone. When evaluated independently, a prognosis somewhat closer to double-positive patients was recorded for patients who were p16 negative but HPV mRNA positive, while a prognosis closer to that of double-negative patients was recorded for those who were p16 positive, but HPV mRNA negative. In this study, an algorithm has been described whereby confirmatory HPV mRNA testing is conducted in patients where p16 status is not consistent with tumor morphology. This identifies a majority of discordant patients and improves, albeit modestly, the prognostication.