RESUMO
BACKGROUND & AIMS: High intakes of the phytoestrogen lignans and high blood concentrations of its main biomarker, enterolactone, has been associated with a better breast cancer prognosis. We investigated the association between pre-diagnostic plasma concentrations of enterolactone and breast cancer prognosis (i.e. recurrence, breast cancer-specific mortality and all-cause mortality). METHODS: Plasma and data was available from the Danish Diet, Cancer and Health cohort. Information on treatment and clinical characteristics from registries and clinical databases and both pre-diagnostic and diagnostic plasma measurement of enterolactone on a sub-set. Enterolactone was quantified in plasma using a high-throughput LC-MS/MS method. We followed 1457 breast cancer cases from date of diagnosis and until censoring or end-of-follow-up (median 9 years), during this time 404 died (250 of breast cancer) and 267 experienced recurrence. Cox proportional hazards models were used to estimate hazard ratios (HR) with 95% confidence intervals (CI). RESULTS: Plasma enterolactone were borderline significantly associated with lower breast cancer-specific mortality (HRdoubling = 0.93, 95% CI:0.86, 1.00, P = 0.0501), but not associated with all-cause mortality (HRdoubling = 0.95, 95% CI:0.89, 1.01) and recurrence (HRdoubling = 0.96, 95% CI: 0.89, 1.04) in the models adjusted for smoking, schooling, BMI, physical activity and use of menopausal hormones. Adjusting further for clinical characteristics and treatment did not change the results considerably. In the sensitivity analyses, an inverse association was found with all-cause and breast cancer-specific mortality for those where blood was collected ≤5 years before diagnosis. CONCLUSIONS: Overall, no clear association was found between pre-diagnostic plasma concentrations of enterolactone and breast cancer prognosis.