Epidemiology of testicular cancer in the Pacific Basin.

Although a rare tumor, testicular cancer shows substantial international variation in incidence. In whites, the peak incidence occurs at 25-30 years of age, with a second increase in old age. Blacks have much lower rates than do whites. The rate of increase in the incidence and mortality of this cancer has been consistent but low during the past 40 years. Risk factors identified in epidemiology studies of testicular cancer include cryptorchidism (best documented), inguinal hernia, testicular injury, wearing of tight-fitting underclothing, obesity, maternal use of exogenous estrogens during pregnancy, higher social class, and professional occupations. Epidemiological evidence provides two etiologic hypotheses: a relative hormone imbalance, particularly an excess of estrogen, and a failure of normal thermal regulation of the testis. In the Pacific Basin region, notable variation in incidence rates is also seen. High-risk populations include whites, Polynesians (in Hawaii and New Zealand), and Native Alaskans. Low-risk groups include Filipinos (in Hawaii and Manila), Japanese (in Hawaii and Japan), Indians, and Malays. Most of this variation occurs in the younger ages (0-54 yr). Several areas for potentially fruitful research on this cancer in the Pacific region are given.