Cancer plays favourites, certain forms strike more virulently in certain places. Although most of these geographical concentrations remain to be explained, they often provide clues to a custom or climate that causes the peculiarly local disease. One form of cancer traced to specific causes, Burkitt's lymphoma, is linked to environment. Six other factors fairly conclusively established as causes of distinctive cancers are illustrated on the following pages. These causes are surprisingly diverse: local foodstuffs or food-preparation techniques, personal habits and a parasite that lives mainly in the Nile River. Among the most puzzling cancer pockets are those where breast cancer is unusually prevalent. The disease is apparently influenced by many factors - heredity, childbearing, possibly viruses and, according to some authorities, a diet high in fats. None of these suspected causes, however, explains why in all the United States, breast cancer is most common around the Great Lakes.

The concentration of lung cancer in Great Britain and the Southern United States is attributed to cigarette smoking - an almost universal habit - and to industrial pollution in those areas. But no one knows why the states of Georgia and South Carolina should suffer so from esophageal cancer - a widely scattered disease whose suspected causes elsewhere have been isolated. In the Transkei (region of South Africa) many Bantu men contract this cancer because - it is speculated - they drink a maize beer that contains a cancer-causing nitrosamine. Alcohol cunsumption, perhaps in combination with smoking, may be the reason for esophageal cancer in France. And among Iran's nomadic Turkomans, the cause could be their regular fare of sooty bread.

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