Psychiatric Comorbidities Among Rectal Cancer Survivors in South Korea: A Nationwide Population-Based, Longitudinal Study

Abstract

Purpose/Objective(s): Human papillomavirus (HPV) has been implicated in the carcinogenesis of squamous cell carcinoma of the anal canal (SCCA). As seen for other body sites, HPV-negative tumors have been associated with poor prognosis in patients with SCCA. Varying methods have been used to define HPV-positive patients including the presence of p16 expression by immunohistochemistry (IHC) and of HPV DNA by polymerase chain reaction (PCR). Neither approach implies causality and these techniques have not been validated against the presence of HPV E6/7 mRNA in SCCA, which represents the gold standard to define HPVinduced carcinogenesis. We hypothesize that p16 IHC serves as an acceptable surrogate to identify HPV-mediated carcinogenesis in SCCA in comparison to the gold standard of E6/7 mRNA expression by in situ hybridization. Materials/Methods: Samples from 27 patients treated for SCCA at a single institution were analyzed using a tissue microarray. Concordance between p16 positivity and E6/7 mRNA expression was evaluated for the 25 patients for whom data on both parameters were available. p16 status was assessed with IHC by a single pathologist blinded to HPV E6/7 mRNA expression; positivity was defined as strong nuclear and cytoplasmic expression in a full thickness segment containing at least 10-20 cells. RNA in situ hybridization was used to determine E6/7 mRNA expression from high-risk HPV subtypes by the microscopic visualization of brown, punctate dots present in the nucleus or cytoplasm. Sensitivity, specificity, and positive predictive value (PPV) were assessed using mRNA expression as the gold standard. Results: Among the 25 patients evaluated, 24 (96%) had the presence of E6/7 mRNA, implying HPV-mediated causality in the majority of patients. p16 and E6/7 mRNA results were concordant in 24/25 specimens (97%). Of the 24 concordant samples tested, there were 23 true positives (p16+ and E6/7 mRNA+) and one true negative (p16-and E6/7-). One specimen was discordant between p16 and E6/7 mRNA (4%). This specimen was p16-but E6/7 mRNA+ (false negative). Multiple slides from the paraffin blocks confirmed this false negative. No patients expressed p16 without the presence of E6/7 mRNA. This resulted in a sensitivity of 96% and a specificity of 100%. PPV of p16 IHC for E6/7 mRNA expression was 100%. Conclusion: In this study, the majority of SCCA cases were caused by HPV as deemed by presence of E6/7 mRNA. The clinically prevalent method of p16 IHC showed excellent concordance with the gold standard of E6/7 mRNA expression and demonstrated its ability to serve as a reliable and widely available surrogate for identifying HPV-induced SCCA. Efforts at treatment intensification in the HPV-negative cohort can reliably use absence of p16 expression as a means of stratification.