Effect of soybean on breast cancer according to receptor status: A case–control study in Japan

The possible association of high soy food consumption with low incidence of breast cancer in Asian countries has been widely investigated, but findings from epidemiologic studies have been inconsistent. Breast cancers defined by receptor status, estrogen receptor (ER), progesterone receptor (PR) and human epidermal growth factor receptor 2 (HER2) may have distinct etiologic factors. Here, we conducted a case-control study to clarify associations between intake of soybean products and breast cancer risk according to receptor status. A total of 678 breast cancer cases and 3,390 age- and menopausal status-matched noncancer controls were included. Odds ratios (ORs) with 95% confidence intervals (CIs) were estimated using conditional logistic models adjusted for potential confounders. On analysis according to receptor status, we observed a significantly reduced risk of ER-positive (ER+) (top tertile OR = 0.74; 95% CI, 0.58-0.94; trend p = 0.01) and HER2-negative (HER2-) tumors (top tertile OR = 0.78; 95% CI, 0.61-0.99; trend p = 0.04). Further, when the 3 receptors were jointly examined, a reduced risk was observed only in patients with ER+/PR+/HER2- tumor (top tertile OR = 0.73; 95% CI, 0.54-0.97; trend p = 0.03). These findings indicate that the protective effect of soy against breast cancer risk differs by receptor status.