Dietary intake and breast cancer among carriers and noncarriers of BRCA mutations in the Korean Hereditary Breast Cancer Study.

BACKGROUND Soy intake is associated with a lower risk of breast cancer. However, it is unclear whether the same reduction in risk associated with high soy intake is also applicable to familial or genetic breast cancer. OBJECTIVE The aim of this study was to assess the dietary factors among carriers and noncarriers of BRCA mutations in the Korean Hereditary Breast Cancer Study (KOHBRA). DESIGN The KOHBRA Study is an ongoing project composed of affected breast cancer patients and familial members of breast cancer cases with BRCA mutations. To assess the association between dietary diversity and breast cancer risk, an HR was estimated by comparing affected subjects with their familial nonaffected members. To assess the interaction between the combination of BRCA mutation and diet diversity, the case-only OR (COR) was estimated by comparing BRCA mutation carriers and noncarriers only in affected subjects. RESULTS Soy product intake was associated with a lower risk of breast cancer in carriers (HR: 0.39; 95% CI: 0.19, 0.79 for the highest quartile). The highest quartile of meat intake was associated with a higher risk of breast cancer regardless of BRCA mutation in carriers (HR: 1.97; 95% CI: 1.13, 3.44) and noncarriers (95% CI: 1.41; 1.12, 1.78). The associations of meat intake and soybean intake for breast cancer were more prominent in BRCA2 mutation carriers. In the analysis with only cases, the highest quartile of soy intake, but not meat intake, was associated with BRCA-related breast cancer (COR: 0.57; 95% CI: 0.36, 0.91). CONCLUSION Our study suggests that soy product consumption is associated with lower breast cancer risk and it had an interaction with BRCA mutation.