Introduction

The geographical distribution of cancer of the esophagus is the most dramatic of any type of cancer (Day et al. 1982). There are large differences in incidence from one country to another, and also from one area to another within any country. In several regions the high- and lowincidence areas are very sharply demarcated.

The global incidence of cancer of the esophagus is one of the highest of all cancers (Parkin et al. 1988; Table 4.1). Combined with cancers of the mouth and pharynx, which often have a similar etiology, the incidence of these upper digestive tract cancers is the highest of any form of cancer. The rate ranges from 0.4/100000 women in the state of Utah, USA, to 174/100000 for women in the Gonbad region of Iran (Kmet et al. 1972). Especially high incidence regions are the notorious ‘cancer belt’, stretching from Iran to China, certain regions in South Africa, and the Normandy district of France (Sales et al. 1985; Fig. 4.1). The astonishingly wide variations in incidence between neighbouring areas have been studied most often in China, where the rate in the Taihang mountains is more than 80/100000 in the Linxian region, and less than 20/100000 in the neighbouring Fanxian county (Cai 1982).

This dramatic epidemiology led to the hope that the causes of the cancer would be relatively easy to identify, but in spite of extensive surveys no single predominating cause has been detected.