P16^INK4A promoter hypermethylation is associated with invasiveness and prognosis of oral squamous cell carcinoma in an age-dependent manner

Oral squamous cell carcinoma (OSCC) is a common cancer worldwide that is highly lethal due to its recurrence and metastasis. Our candidate-based study aimed to link promoter CpG island hypermethylation to OSCC risk assessment. We examined the promoter hypermethylation status of p16^INK4A (p16), glutathione S-transferase pi (GSTP1), O⁶-methylguanine-DNA methyltransferase (MGMT), death-associated protein kinase 1 (DAPK1), RAS-association domain family 1, isoform A (RASSF1A), and E-cadherin (CDH1) genes in OSCC tumors. Quantitative methylation-specific PCR analysis showed a significant increase in promoter hypermethylation of p16 and CDH1 in OSCC tumors relative to paired non-tumorous tissues. The mean age of patients with hypermethylated p16 was lesser than those without (P = 0.027). Multiple logistic regression predicted patients with hypermethylated p16 have higher risks of lymph node invasion (adjusted OR = 6.21, P = 0.030) in young patients and distant metastasis (adjusted OR = 19.23, P = 0.007) in older patients. Moreover, p16 promoter hypermethylation was significantly associated with shortened disease-free survival (P = 0.034) in older patients. Our results suggested that p16 hypermethylation was associated with early incidence of OSCC, increased lymph node invasion in young patients, and poor prognosis in older patients. Further, p16 hypermethylation may also be implicated in age-related tumor invasion in carcinogenesis.