Pre-diagnostic polyphenol intake and breast cancer survival: the European Prospective Investigation into Cancer and Nutrition (EPIC) cohort

The aim was to investigate the association between pre-diagnostic intakes of polyphenol classes (flavonoids, lignans, phenolic acids, stilbenes, and other polyphenols) in relation to breast cancer survival (all-cause and breast cancer-specific mortality). We used data from the European Prospective Investigation into Cancer and Nutrition cohort. Pre-diagnostic usual diet was assessed using dietary questionnaires, and polyphenol intakes were estimated using the Phenol-Explorer database. We followed 11,782 breast cancer cases from time of diagnosis until death, end of follow-up or last day of contact. During a median of 6 years, 1482 women died (753 of breast cancer). We related polyphenol intake to all-cause and breast cancer-specific mortality using Cox proportional hazard models with time since diagnosis as underlying time and strata for age and country. Among postmenopausal women, an intake of lignans in the highest versus lowest quartile was related to a 28 % lower risk of dying from breast (adjusted model: HR, quartile 4 vs. quartile 1, 0.72, 95 % CI 0.53; 0.98). In contrast, in premenopausal women, a positive association between lignan intake and all-cause mortality was found (adjusted model: HR, quartile 4 vs. quartile 1, 1.63, 95 % CI 1.03; 2.57). We found no association for other polyphenol classes. Intake of lignans before breast cancer diagnosis may be related to improved survival among postmenopausal women, but may on the contrary worsen the survival for premenopausal women. This suggests that the role of phytoestrogens in breast cancer survival is complex and may be dependent of menopausal status.