MTNR1A and oral cavity squamous cell carcinoma: Melatonin has been postulated to be a tumor suppressor gene due to its oncostatic effect in various cancers [33,57,58], as such, expression of MTNR1A was found to be frequently silenced through methylation of CpG islands surrounding the MTNR1A promoter in cases of oral squamous cell carcinoma (OSCC) and other primary cancers [59].