A peculiar distribution of esophageal cancer was observed in the Caspian littoral of Iran, where an ad hoc cancer registry has been in operation since 1968. A very high incidence, among the hghest recorded in the world, with a higher incidence in women than in men (male: 108.8 cases per 100,000 population; female: 174.1 per 100,000), was recorded in the northeastern corner of the region; this sparsely populated, semidesert area of the central Asian type, with predominantly saline soils, was settled by Turkomans. A lower incidence with a change in the male-to-female ratio was observed in the southeastern and central parts of the region, which are located in the piedmont area of the Elburz Mountains; these areas have more abundant rainfall and nonsaline soils, and are densely populated by Iranians. A steady decline in the incidence with an increase in the preponderance of male cases was observed toward the west, reaching the lowest figures (male: 17.2 cases per 100,000 population; female: 5.5 per 100,000) in the Caspian rain belt, with its heavily leached soils and somewhat subtropical characteristcs. Changes in the natural vegetation and in the agricultural practices parallel the changing features of the climate.
A multidisciplinary, multidisease, and multifactorial study is in preparation. By plotting the detailed physical, biotic, and cultural characteristics of the selected ecological regions on the intrinsic characteristics of the population groups experiencing different esophageal cancer risk, new and profitable working hypotheses as to the etiology of esophageal cancer might be produced.