Effect of Dietary Intake of Phytoestrogens on Estrogen Receptor Status in Premenopausal Women With Breast Cancer

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Abstract
Although many dietary studies have focused on breast cancer risk, few have examined dietary influence on tumor characteristics such as estrogen receptor (ER) status. Because phytoestrogens may modulate hormone levels and ER expression, we analyzed ER status and phytoestrogen intake in a case-case study of 124 premenopausal breast cancer patients. We assessed intake with a food-frequency questionnaire and obtained ER status from medical records. Rather than focusing on risk, we evaluated whether low intakes were more strongly associated with ER-negative tumors than with ER-positive disease. In logistic regression adjusting for potential confounders, threefold greater risks of ER-negative tumors relative to ER-positive tumors were associated with low intake of the isoflavones genistein (odds ratio, OR = 3.50; 95% confidence interval, CI = 1.43–8.58) and daidzein (OR = 3.10; 95% CI = 1.31–7.30). Low intake of the flavonoid kaempferol (OR = 0.36; 95% CI = 0.16–0.83), the trace element boron (OR = 0....