Esophageal cancer is one of the most common cancers world-wide, having a higher global incidence than the much-studied cancer of the liver. When added to oral and pharyngeal cancers, which have a similar etiology, cancers of the upper alimentary tract form the most prevalent cancers world-wide (Parkin et al. 1988). The difference in rate between high and low incidence areas around the world is extreme, ranging from 0.4/100000 for women in the state of Utah, USA, to 170/100 000 in the Gonbad region of Northern Iran. Even within any country, the geographical distribution of the cancer is often very sharply demarcated, exceptionally high-risk regions neighbouring onto districts with a much lower risk. At the French/Belgian and the Kenya/Uganda borders there is a sharp change in incidence at the political boundaries. Epidemiological studies carried out in these situations have very strongly implicated a variety of risk factors, notably alcohol consumption, deficiencies of certain micronutrients, consumption of food contaminated by mycotoxins, and a low consumption of fresh fruit and vegetables. None of these factors, however, has been shown to cause esophageal cancer in experimental animals.

Thousands of chemicals have been tested for carcinogenicity, but the only compounds found to be potent carcinogens for the esophagus in animal experiments are the nitrosamines. All species tested were found to be susceptible, from amphibia to primates, and there is no apparent reason why man should be excepted.