Trends in frequency of latent prostate carcinoma in Japan from 1965-1979 to 1982-1986.

By analyzing serial step-sections of whole prostate obtained at autopsy, we determined the chronologic change of the frequency of latent prostate tumor in Japan in two periods: 1965-1979 and 1982-1986. Methods of specimen preparation and examination were identical for both periods. The frequency with which latent prostate carcinoma was found in the 660 samples for 1982-1986 was 34.6% and was significantly higher than the 22.5% seen in the 576 observed for 1965-1979 (P less than .0001). This significant finding can be attributed to an increase in the frequency of latent infiltrative tumor (LIT). However, the increase in the frequency of noninfiltrative tumor (LNT) was less significant (P = .045). Both sets of specimens were subsequently combined and reanalyzed according to the year of birth of the decedents. The LIT has progressively increased in frequency in each age-specific category. By morphometry, we determined that the mean tumor volume decreased due to an increase in the number of smaller tumors during the study periods. Although the frequency of latent prostate carcinoma and the LIT:LNT in the samples obtained most recently were comparable to those of U.S. whites, cancer incidence and mortality rates remain lower in Japan. Apparently, the initial step in the induction of prostate carcinoma in indigenous Japanese is now similar to that in U.S. whites. The rates of clinical carcinoma in Japan are still low when compared with those in the United States and countries in Western Europe, but our findings may presage a time when these differences may be greatly reduced or nonexistent.