Role of DNA methylation‐based mitotic ageing indices in oral cancer development and recurrence.

Objective: DNA methylation data can be used to derive mitotic indices from complex tissues. Here, we assessed if the DNA methylation‐derived mitotic ageing indices are associated with oral squamous cell carcinoma (OSCC) development and recurrence‐free survival (RFS). Methods: DNA methylation‐based mitotic indices (MitoticAge, TNSC and hypoSC) were derived using algorithms "MitoticAge" and "epiTOC2" for the discovery [non‐malignant (n = 22), premalignant (n = 22) and OSCC (n = 68) tissues] and validation datasets (GSE87053, GSE136704 and TCGA‐HNSCC). Differences in mitotic indices between non‐malignant, premalignant and OSCC tissues were assessed. Finally, the association between estimated mitotic indices and RFS was evaluated in OSCCs. Results: In the discovery and validation datasets, increased mitotic ageing was observed in OSCC compared to non‐malignant and premalignant oral tissues. HPV‐positive HNSCCs had higher mitotic index TNSC. Mitotic age index hypoSC was associated with RFS in OSCC (p = 0.011, HR 2.61, 95% CI 1.24–5.48). Conclusions: DNA methylation‐derived mitotic indices are associated with OSCC development and RFS. Thus, DNA methylation‐derived mitotic indices may be a valuable research tool to reliably estimate the cumulative number of stem cell divisions in malignant and non‐malignant oral tissues. Future research utilizing mitotic indices for predicting clinical outcomes in OSCC is warranted. [ABSTRACT FROM AUTHOR]