Smokeless tobacco, viruses and oral cancer.

Oral Squamous Cell Carcinoma (OSCC) is the most common epithelial malignancy in the oral cavity. OSCCs and their variants constitute over 90% of oral malignancies, and the disease is associated with poor prognosis. OSCC is a complex malignancy where environmental factors, viral infections, and genetic alterations most likely interact, and thus give rise to the malignant condition. The International Agency for Research on Cancer (IARC) in 2007 concluded: "there is sufficient evidence in humans to establish smokeless tobacco as carcinogenic, i.e. smokeless tobacco causes cancer of the oral cavity and pancreas". ST products contain a large array of carcinogens, although the number found is actually smaller than in cigarette smoke. Worldwide, ST products have many different names depending on the region where it is produced. However, there are two main types of ST, chewing tobacco and snuff. It is estimated that approximately 150 million people in the world use ST. Herein, we review available literature regarding smokeless tobacco and oral Carcinogenesis. We also discuss the role of viral infections in combination with ST in OSCC development.