Effect of Dietary Intake of Isoflavones on the Estrogen and Progesterone Receptor Status of Breast Cancer

To examine if higher intake of isoflavones prior to diagnosis was associated with a positive status of estrogen receptors (ER) and progesterone receptors (PR) in breast tumor tissue, a retrospective study was conducted in 2004 to 2005 in 756 Chinese women with histologically confirmed breast cancer. We administered a food frequency questionnaire by face-to-face interview to assess the intake of the isoflavones daidzein and genistein. Unconditional logistic regression analysis was used to estimate odds ratios (ORs) and 95% confidence intervals (CIs) adjusted for potential confounders. Comparing the highest to lowest intake quartiles, the adjusted ORs for daidzein were 1.94 (95% CI = 1.20-3.32) and 2.18 (95% CI = 1.28-3.73) for ER positive and PR positive tumors, respectively, in premenopausal patients. The ORs for both ER and PR positive status combined were 2.48 (95% CI = 1.37-4.49) for daidzein and 1.94 (95% CI = 1.21-3.14) for genistein in premenopausal patients with statistically significant tests for trend. There was little or no evidence of associations in postmenopausal patients. We conclude that higher intake of daidzein and genistein before diagnosis was associated with ER and PR positive status in premenopausal Chinese women with breast cancer. The association might confer a more favorable prognosis.