Incidence
Squamous cell cancers of the upper aerodigestive tract are a significant global problem with 380,000 new cases diagnosed worldwide in 1980. Almost three quarters of these cases occur in developing countries, and in some countries (e.g., India, Pakistan, Bangladesh) these cancers may account for almost 25% of all cancers. In parts of India, this figure may rise to almost 50%. In developed countries the incidence is less common, ranking this type as the eighth most common cancer; however, the incidence varies from country to country (e.g., in some areas of France it is extremely common). In the United States, the incidence of these cancers has stabilized, comprising 3% of all cancers in men and 2% in women, and results in 2% of all cancer deaths in males and 1% in females. In general, the incidence is greater in males than in females, and these cancers are more common in the elderly, although the disease is being seen more commonly in females and in younger patients.

Etiology
The exact origin or cause of squamous cell cancer is not well understood, but it appears to develop in a susceptible host, with the process being precipitated by environmental factors. These include tobacco, alcohol, radiation, drugs, diet, pollution, viral infections, and other unknown factors. Of these, tobacco (smoked or smokeless) is the most important, with the majority of cases occurring in those who use tobacco products. Tobacco and alcohol appear to have a synergistic effect in the development of these cancers. There is some suggestion that there exists a genetic predisposition to the carcinogenic effects of tobacco products. Other factors (e.g., radiation exposure, syphilis, viral infections, lichen planus, vitamin deficiencies) all may be implicated but appear to have a lesser role.