Worldwide, oral squamous cell carcinoma ranks the sixth most common cancer and accounts for 3-5% of all human malignancies. In India, oral cancer ranks as no. 1 amongst all cancers in males and no. 3 amongst all cancers in female. Tobacco smoking betel quid chewing and alcohol consumption are established risk factors associated with oral squamous cell carcinoma and most common oral pre-malignancies. All the above forms of tobacco are known to contain hydrocarbons and several potent nitrosamines which are carcinogenic and act via alterations in DNA thus playing key role in promotion of oral cancer.
OSCC arises as a result of multiple molecular events that develop from combined influences of an individual. Genetic predisposition, immunodeficiency and external agents such as dietary factors and viruses like Human Papilloma Virus and Epstein Barr Virus. Accumulation of genetic alterations can lead to the development of premalignant lesions and subsequent invasive carcinoma, correct diagnosis of premalignant oral lesions enables treatment before progression. The most common premalignant lesions in oral cavity are leukoplakia without dysplasia, submucous fibrosis and oral lichen planus. Both genetic and epigenetic changes are known to contribute tumorigenesis in humans. While genetic alterations refer to irreversible changes in DNA sequencing leading to oncogene activation or tumour suppressor gene inactivation. Epigenetic changes denote reversible modifications in gene expression without any alterations in gene sequence.
DNA methylation is the most significant epigenetic modification. Methylation of cytosine at CpG dinucleotide is a common feature in many higher eukaryotic genomes. This cytosine modification has become intensively epigenetic DNA marker. DNA methylation proposed to be a useful marker for cancer diagnosis, screening, surveillance in high-risk individuals, monitoring of minimal residual disease and determining optimal therapeutic options. Therefore, there are increasing demand for reliable assays to measure DNA methylation, particularly for tissues.