A new study has reported that women in the highest fourth of circulating enterolactone levels have a 35% lower risk of postmenopausal breast cancer than those in the lowest quartile. Enterolactone is a lignan phytoestrogen derived from a variety of foods such as seeds, whole grain products, and some fruits and vegetables. Lignans are found mainly in woody or fibrous tissues. Several population studies have reported that lignans may protect against breast cancer. Participants included 1,250 breast cancer cases and 2,164 cancer-free controls. Circulating enterolactone levels were measured using blood draws. Also examined was whether estrogen receptor (ER), progesterone receptor (PR), and HER2 status influenced the association. The authors also performed a meta-analysis of seven other studies that previously examined the link between enterolactone levels and breast cancer risk.

In the current study, postmenopausal breast cancer risk was found to decrease with increasing serum enterolactone levels. This association was found for both hormone receptor positive (ER+/PR) and hormone receptor negative (ER-/PR-) disease, but was stronger for ER-/PR- (including triple negative tumors). HER2 status did not influence the association for ER-/PR- tumors. The meta-analysis also yielded a significant reduced pooled risk estimate when comparing the highest to the lowest quantiles of enterolactone levels. The authors conclude that they found strong evidence for a significant inverse association between serum enterolactone and postmenopausal breast cancer risk, which was stronger for ER-PR- than for ER+PR+ tumors but not influenced further by HER2 expression. Taken together with other studies, the evidence supports an inverse association between higher serum enterolactone levels and postmenopausal breast cancer risk.