Genetic etiology of oral cancer.

Head and neck squamous cell carcinoma (HNSCC) is the sixth most common cancer worldwide. It accounts for 2.5% of all new cancer cases and 1.9% of all cancer deaths annually. More than 90% of oral cancers (occurring in the mouth, lip, and tongue) are oral squamous cell carcinoma. The incidence rate of oral cancer varies widely throughout the world, with an evident prevalence in South Asian countries. This high incidence occurs in correlation with oral cancer-associated behaviors such as alcohol, tobacco use. Researchers have reported that these behaviors lead to genetic variations in tumor suppressor genes (APC, p53), proto-oncogenes (Myc), oncogene (Ras) and genes controlling normal cellular processes (EIF3E, GSTM1). Processes such as segregation of chromosomes, genomic copy number, loss of heterozygosity, telomere stabilities, regulations of cell-cycle checkpoints, DNA damage repairs and defects in notch signaling pathways are involved in causing oral cancer. In order to develop preventive and therapeutic options, it is necessary to comprehend the basic molecular mechanisms forcing oral tumorigenesis. This review examines, in detail, the mechanisms of genetic alteration which are considered to be responsible for the initiation of oral cancer.