Similar Effect of P16 Hydroxymethylation and True Methylation on Prediction of Malignant Transformation of Oral Epithelial Dysplasia: A Prospective Study

Abstract

Background: Total P16 methylation (P16M), including P16 hydroxymethylation (P16H) and true-P16M, correlates with malignant transformation of oral epithelial dysplasia (OED). Both true-P16M and P16H are early events in carcinogenesis. Aim: The aim of this study is to prospectively determine if discrimination of true-P16M from P16H similarly is necessary for prediction of cancer development from OEDs. Methods: Patients (n = 265) with mild or moderate OED were recruited into the double-blind 2-center cohort. Total-P16M and P16H were analyzed using the 115-bp MethyLight, TET-assistant bisulfite (TAB) methylation-specific PCR (MSP), and TAB-sequencing. Total-P16M-positive and P16H-negative samples were defined as true-P16M-positive. Progression of OEDs was monitored for a minimum 24 months follow-up period. Results: P16H was detected in 23 of 73 (31.5%) total-P16M-positive OEDs. Follow-up information was obtained from 247 patients with an ultimate compliance of 93.2%. OED-derived squamous cell carcinomas were observed in 13.0% (32/247) patients during the follow-up (median, 41.0 months). The cancer progression rate for total-P16M-positive patients was significantly increased when compared with total-P16M-negative patients (23.3% vs 8.6%; adjusted odds ratio = 2.67 [95% CI: 1.19-5.99]). However, the cancer progression rate was similar between P16H- and true-P16M-positive OEDs (26.1% [6/23] vs 22.0% [11/50]; odds ratio = 0.80 [95% CI: 0.22-2.92]). The progression-free survival was also similar for these patients. Conclusion: P16H and true-P16M are similar biomarkers for determining malignant potential of OEDs. Discrimination of P16H from true-P16M, at least in OED, may be not necessary in clinical applications.