Plasma Isoflavones and the Risk of Lung Cancer in Women: A Nested Case-Control Study in Japan

Background: Although several epidemiologic studies have found that isoflavone intake assessed by questionnaire is associated with a decreased risk of lung cancer, no prospective study has investigated this association using blood concentrations of isoflavones. Methods: We conducted a nested case-control study within a population-based prospective cohort study. A total of 24,127 women aged 40 to 69 years who returned the baseline questionnaire and provided blood samples were observed from 1990 through 2006. During a median follow-up period of 13.5 years, 126 newly diagnosed lung cancer cases were identified. For each case, we selected two controls matched for age, area, smoking status, and condition of blood draw. A conditional logistic regression model was used to estimate the odds ratios (ORs) and 95% CIs of lung cancer in relation to plasma concentrations of genistein, daidzein, glycitein, equol, and total isoflavones. Results: After exclusion of 20 lung cancer cases diagnosed in the first 3 years after blood collection, an inverse association was found between plasma genistein concentration and lung cancer risk. The multivariate-adjusted OR (95% CI) of lung cancer in the highest quintile of plasma genistein concentration as compared with that in the lowest quintile was 0.31 (0.12, 0.86; P for trend -0.085). Other isoflavones and total isoflavones were not associated with a significant decrease in the risk of lung cancer. Conclusion: Plasma genistein concentration was inversely associated with lung cancer risk in Japanese women. Impact: Our data support the previously observed association between isoflavone intake and lung cancer risk. Cancer Epidemiol Biomarkers Prev; 20(3); 419-27. (C)2011 AACR.