Thyroid Cancer in the Pacific

Extract

Thyroid cancer is one of only a few cancers that occurs more frequently among women than among men, with incidence rates typically two to three times higher among females than among males in most parts of the world ( 1 ). What is less well-known is that rates of thyroid cancer vary substantially geographically. Herein, we describe the international variation in thyroid cancer occurrence, noting the remarkable clustering of elevated incidence rates among residents of multiple islands in the Pacific.

Age-adjusted (world standard) annual thyroid cancer incidence rates per 100000 population among females and males during the 1980s for selected areas of Europe, North and South America, Asia, Australia, and island nations in the Atlantic and Pacific Oceans are shown in Fig. 1 . In most continental nations, the incidence rates of thyroid cancer among women range from about two to about six cases per year per 100 000 population. This is the situation throughout Europe, North and South America, Asia, and Australia. In contrast, rates among numerous Pacific island groups exceed six per 100 000. The world's highest incidence rates (exceeding 15 per 100 000) are reported among females in Hawaii, French Polynesia, and New Caledonia. The high rates in the Pacific islands tend to affect all ethnic groups, although considerably more so native (Polynesian, Melanesian) than European (white) residents. Among western countries, the highest rates of thyroid cancer are reported for the island of Iceland, while no excess is seen among residents of islands of the South Atlantic ocean. The geographic patterns are generally similar for both sexes, although the variation is most pronounced among females.