Comparative study of latent carcinoma of the prostate among Japanese in Japan and Hawaii.

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The age-adjusted mortality rates from cancer of the prostate among Japanese in Hawaii are more closely aligned to the high rates of U.S. whites than to the low rates of native Japanese. As the first step toward clarification of the underlying causes for this increase, latent carcinoma of the prostate in Hawaiian Japanese and native Japanese was studied with special reference to its prevalence and histologic features. We examined 239 prostates of native Japanese and 158 of U.S. Japanese in Hawaii, which were removed at autopsy from males over 50 years old. Special attention was paid to comparability of examination methods and histologic diagnoses. The age-adjusted prevalence of latent cancer of the prostate did not differ significantly between native and Hawaiian Japanese. Nevertheless, in Hawaiian Japanese, latent cancer tended to proliferate and invade, and the prevalence of the proliferative type of latent carcinoma was higher in the migrant group. Factors that promote the growth of cancer cells appeared more effective in Hawaiian Japanese than in those who always lived in japan. Environmental factors were suggested as the probable cause for this difference.