Serum Levels of Prostate-Specific Antigen Among Japanese-American and Native Japanese Men

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Abstract
Background: Fourfold to sixfold higher prostate cancer rates in Japanese-American men in the United States compared with Japanese men in Japan have been cited to support a role for environmental risk factors in the etiology of the disease. To examine the hypothesis that part or all of the elevated prostate cancer rates in Japanese-American men may reflect more intensive prostate cancer screening in the United States than in Japan, we compared prostate-specific antigen (PSA) levels in community-based samples of serum from men without prostate cancer. Methods: Japanese-American men aged 40–85 years and native Japanese men aged 40–89 years with no history of prostate cancer provided sera, respectively, in the United States from March 1990 through March 1992 (n = 237) or in Japan from January 1992 through December 1993 (n = 3522). Age-specific PSA levels were used to estimate the prevalences of undetected prostate cancer in the two populations. Results: Age-specific mean PSA levels were significantly lower in Japanese-Americans than in native Japanese (two-sided P <.001). The prevalence of an elevated PSA level increased with age in both populations and exceeded 5% among men aged 60 years or more. Combined with data on prevalence of detected prostate cancer in the two populations, our data suggest that some 10.0% of Japanese-Americans aged 75 years have prostate cancer, with 31% of that fraction remaining undiagnosed. The corresponding estimates in Japan are a total cancer prevalence of 5.4%, of which 81% has not been detected clinically. Conclusions: The total cancer prevalence ratio 10.0/5.4 = 1.9 (95% confidence interval = 1.5–2.3) in Japanese-American men compared with Japanese men in Japan suggests an increased risk for Japanese-American men, but of less magnitude than the fourfold to sixfold increase indicated by the incidence data.