ABSTRACT
Soy-food intake has previously been associated with reduced breast cancer risk. Epidemiological evidence for subgroups of breast cancer, particularly by menopausal and hormone receptor status, is less consistent. To evaluate the role of hormone receptor and menopausal status on the association between soy-food intake and breast cancer risk, we measured usual soy-food intake in adolescence and adulthood via food frequency questionnaire in 70,578 Chinese women, aged 40-70 years, recruited to the Shanghai Women's Health Study (1996-2000). After a median follow-up of 13.2 years (range:0.01-15.0), 1,034 incident breast cancer cases were identified. Using Cox models, we found that adult soy intake was inversely associated with breast cancer risk (hazard ratio-HR) for fifth versus first quintile soy protein intake=0.78; 95% confidence interval (CI):0.63-0.97). The association was predominantly seen in premenopausal women (HR=0.46; 95% CI:0.29-0.74). Analyses further stratified by hormone receptor status showed that adult soy intake was associated with significantly decreased risk of ER+/PR+ breast cancer in postmenopausal women (HR=0.72; 95% CI:0.53-0.96) and decreased risk of ER-/PR- breast cancer in premenopausal women (HR=0.46; 95% CI:0.22-0.97). The soy association did not vary by HER2 status. Furthermore, we found that high soy intake during adulthood and adolescence was associated with reduced premenopausal breast cancer risk (HR=0.53; 95% CI:0.32-0.88; comparing third versus first tertile) while high adulthood soy intake was associated with postmenopausal breast cancer only when adolescent intake was low (HR=0.63; 95% CI:0.43-0.91). Our study suggests that hormonal status, menopausal status, and time window of exposure are important factors influencing the soy-breast cancer association. This article is protected by copyright. All rights reserved.
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