Assessing the Reliability and Positive Predictive Value of p16 as a Surrogate for Human Papillomavirus-Mediated E6/7 mRNA Expression in Squamous Cell Carcinoma of the Anal Canal

Background: Human papillomavirus has been implicated in the carcinogenesis of squamous cell carcinoma of the anal canal. p16 expression and the presence of human papillomavirus DNA have been used to define human papillomavirus-positive patients, but neither approach has been validated against the standard of human papillomavirus E6/7 mRNA expression at this disease site. Objective: This study aimed to evaluate the acceptability of p16 immunohistochemistry as a surrogate to E6/7 mRNA expression in identifying human papillomavirus-mediated squamous cell carcinoma of the anal canal. Design: This was a retrospective analysis of a previously constructed tissue microarray. SETTINGS: This study was conducted at a tertiary academic center. Patients: Biopsies and resection specimens from patients diagnosed with squamous cell carcinoma of the anal canal at the study institution from 2005 to 2015 were reviewed for sample adequacy. Main Outcome Measures: Concordance between p16 positivity by immunohistochemistry and E6/7 mRNA expression by in situ hybridization was evaluated. Sensitivity, specificity, and positive predictive value were assessed. Results: Among the 25 patients evaluated, p16 and E6/7 mRNA results were concordant in 24 of 25 specimens (96%). Of the 24 concordant samples, there were 23 true positives (p16+ and E6/7+) and 1 true negative (p16- and E6/7-). One specimen was discordant (p16- and E6/7+) between p16 and E6/7 mRNA (4%). This resulted in a sensitivity of 96% and a specificity of 100%. Positive predictive value of p16 immunohistochemistry for E6/7 mRNA expression was 100%. Limitations: This study was limited by its retrospective nature and small sample size. It only assessed diagnostic parameters rather than prognostic implications. Conclusions: In this study, the clinically prevalent method of p16 immunohistochemistry showed excellent concordance with the standard of E6/7 mRNA expression and demonstrated its potential to serve as a surrogate for identifying human papillomavirus-induced squamous cell carcinoma of the anal canal.