Michael K. Reger, PhD, MPH: No relevant financial relationship(s) with ineligible companies to disclose.
Objectives: The purpose of this study is to investigate if the intake of phytoestrogens influences the risk of different types of breast cancer.
Methods: During a median follow-up of 11.8 years, 2,364 cases of breast cancer have been identified among 51,530 women in the Prostate, Lung, Colorectal, and Ovarian Cancer Screening Trial (PLCO). Dietary intake of phytoestrogens was assessed using a food frequency questionnaire and divided into tertiles (T) upon the removal of outliers. Cox proportional hazard regression analysis was performed to estimate the hazard ratios (HRs) and 95% confidence intervals (CI) for dietary phytoestrogens in relation to risk of breast cancer development and different subtypes, including those classified by human epidermal growth factor receptors (HER2), estrogen receptors (ER), progesterone receptors (PR), total hormone receptors (HR), and triple negative breast cancer (TNBC).
Results: Statistically significant differences were observed across demographic and anthropometric variables according to breast cancer status. Breast cancer cases were more likely to have a higher education level, drink alcohol, have a family history of breast cancer, and have taken female hormones. No statistically significant associations were observed between the intake of phytoestrogens and overall breast cancer development after adjustment for confounders. When comparing the risk of subtype development in the breast cancer only population, a decreased risk of ER+ breast cancer (T3 HR: 0.64 [95% CI: 0.44 – 0.95]), PR+ breast cancer (T3 HR: 0.64 [95% CI: 0.43 – 0.96]), and HR+ breast cancer (T3 HR: 0.60 [95% CI: 0.40 – 0.92]) was associated with the intake of total isoflavones. Similar decreased risks were associated with the intake of coumestrol. Total isoflavone intake was also associated with an increased risk of TNBC (T2 HR: 9.55 [95% CI: 1.07 – 85.1]).
Conclusions: Hormone receptor-positive breast cancers have a higher survival rate due to the availability of targeted receptor hormone therapies. These results suggest that there may be unexplored dietary avenues to reduce the risk of development of less responsive subtypes, however further study is needed to confirm these results in a population with higher variability of phytoestrogen intake and an increased sample size of TNBC.
