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Proportion of premenopausal and postmenopausal breast cancers attributable to known risk factors

Breast cancer risk factors have been widely explored individually; however, little is known about their combined impact. Researchers included 67,634 women from the French E3N prospective cohort, aged 42-72 at baseline. During a 15-year follow-up period, 497 premenopausal and 3,138 postmenopausal invasive breast cancer cases were diagnosed.

Population-attributable fractions (PAFs) were used to estimate cases proportions attributable to risk factors under hypothetical scenarios of lowest exposure. overall premenopausal and postmenopausal invasive breast cancers and tumour subtypes (ER status and HER2 expression) were examined.

Premenopausal breast cancer was not significantly attributable to non-behavioural (61.2%, -15.5% to 91.88%) nor to behavioural (39.9%, -71.0% to 93.9%) factors, contrary to postmenopausal breast cancer (41.9%, 4.5% to 68.7% and 53.5%, 12.8% to 78.7%, respectively). Individually, the highest statistically significant PAFs were obtained in premenopause for birth weight (33.6%, 5.7% to 56.6%) and age at menarche (19.8%, 5.2% to 33.6%) for non-behavioural factors and in postmenopause for history of benign breast diseases (14.9%, 11.6% to 18.0%) and age at menarche (9.7%, 3.9% to 15.5%) for non-behavioural factors and for body shape at menarche (17.1%, 9.7% to 24.3%), use of hormone replacement therapy (14.5%, 9.2% to 19.6%), dietary pattern (10.1%, 2.6% to 17.4%) and alcohol consumption (5.6%, 1.9% to 9.3%) for behavioural factors. These proportions were higher for ER+, HER2- and ER+/ HER2- postmenopausal breast cancers. The data supports the hypothesis that in postmenopause, never starting unhealthy behaviours can reduce the number of diagnosed breast cancers.

Source: Proportion of premenopausal and postmenopausal breast cancers attributable to known risk factors: Estimates from the E3N-EPIC cohort. Dartois L, Fagherazzi G, Baglietto L, Boutron-Ruault MC, Delaloge S, Mesrine S, Clavel-Chapelon F. Int J Cancer. 2016 Jan 12. doi: 10.1002/ijc.29987.

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