Originally published as JCO Early Release 10.1200/JCO.2008.16.8807 on November 17 2008

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Plasma Isoflavones and Subsequent Risk of Prostate Cancer in a Nested Case-Control Study: The Japan Public Health Center

Norie Kurahashi, Motoki Iwasaki, Manami Inoue, Shizuka Sasazuki, Shoichiro Tsugane

From the Epidemiology and Prevention Division, Research Center for Cancer Prevention and Screening, National Cancer Center, Tokyo, Japan

Corresponding author: Norie Kurahashi, MD, PhD, Epidemiology and Prevention Division, Research Center for Cancer Prevention and Screening, National Cancer Center, 5-1-1 Tsukiji Chuo-ku Tokyo 104-0045 Japan; e-mail: nkurahas{at}gan2.res.ncc.go.jp

Purpose The incidence of prostate cancer is much lower in Japanese than Western populations. Given the preventive effects of isoflavones on carcinogenesis in the prostate in many nonhuman studies and the high consumption of isoflavones in Japanese, this low incidence may be partly due to the effects of soy.

Patients and Methods We conducted a nested case-control study within the Japan Public Health Center–based Prospective Study. A total of 14,203 men aged 40 to 69 years who had returned the baseline questionnaire and provided blood samples were observed from 1990 to 2005. During a mean of 12.8 years of follow-up, 201 newly diagnosed prostate cancers were identified. Two matched controls for each case were selected from the cohort. Conditional logistic regression model was used to estimate the odds ratios (ORs) and 95% CIs for prostate cancer in relation to plasma levels of isoflavone.

Results Plasma genistein level tended to be inversely associated with the risk of total prostate cancer. Although plasma daidzein showed no association, the highest tertile for plasma equol, a metabolite of daidzein, was significantly associated with a decreased risk of total prostate cancer (OR = 0.60; 95% CI, 0.36 to 0.99; P_trend = .04). These inverse associations were strengthened after analysis was confined to localized cases, with ORs in the highest group of plasma genistein and equol compared with the lowest of 0.54 (95% CI, 0.29 to 1.01; P_trend = .03) and 0.43 (95% CI, 0.22 to 0.82; P_trend = .02), respectively. Plasma isoflavone levels were not statistically significantly associated with the risk of advanced prostate cancer.

Conclusion Isoflavones may prevent the development of prostate cancer.

published online ahead of print at www.jco.org on November 17, 2008.

Supported by Grants-in-Aid for Cancer Research (Grant No. 19shi-2), for the 3rd Term Comprehensive 10-Year Strategy for Cancer Control (Grant No. H18-sanjigan-ippan-001), and for Research on Risk of Chemical Substances (Grant No. H17-kagaku-ippan-014) from the Ministry of Health, Labour and Welfare of Japan, and Grants-in-Aid for Scientific Research on Priority Areas from the Ministry of Education, Culture, Sports, Science and Technology (Grant No. 17015049).

Authors’ disclosures of potential conflicts of interest and author contributions are found at the end of this article.

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