Abstract
BackgroundWomen with an advantaged socioeconomic position (SEP) have a higher risk of developing breast cancer (BC). The reasons for this association do not seem to be limited to reproductive factors and remain to be understood. We aimed to investigate the impact of lifecourse SEP from childhood and social mobility on the risk of BC considering a broad set of potential mediators.MethodsWe used a discovery-replication strategy in two European prospective cohorts, E3N (N = 83,436) and EPIC-Italy (N = 20,530). In E3N, 7877 women were diagnosed with BC during a median 24.4 years of follow-up, while in EPIC-Italy, 893 BC cases were diagnosed within 15.1 years. Hazard ratios (HR) were estimated using Cox proportional hazard models on imputed data.ResultsIn E3N, women with higher education had a higher risk of BC (HR [95%CI] = 1.21 [1.12, 1.30]). This association was attenuated by adjusting for reproductive factors, in particular age at first childbirth (HR[95%CI] = 1.13 [1.04, 1.22]). Health behaviours, anthropometric variables, and BC screening had a weaker effect on the association. Women who remained in a stable advantaged SEP had a higher risk of BC (HR [95%CI] = 1.24 [1.07; 1.43]) attenuated after adjustment for potential mediators (HR [95%CI] = 1.13 [0.98; 1.31]). These results were replicated in EPIC-Italy.ConclusionsThese results confirm the important role of reproductive factors in the social gradient in BC risk, which does not appear to be fully explained by the large set of potential mediators, including cancer screening, suggesting that further research is needed to identify additional mechanisms.
Highlights
Women with an advantaged socioeconomic position (SEP) have a higher risk of developing breast cancer (BC)
We further examined the impact of health behaviours, anthropometric characteristics, reproductive factors, family history of hormonerelated cancer, and BC screening on these relationships
Women diagnosed with BC were more likely to have a family history of a hormonerelated cancer, to be Menopausal hormone therapy (MHT) ever user, to have fewer children, to have been older at first childbirth, not to have breastfed, to have a longer reproductive lifespan, to be in pre-menopause at baseline, and to have ever participated in mammographic screening before inclusion
Summary
Women with an advantaged socioeconomic position (SEP) have a higher risk of developing breast cancer (BC). The reasons for this association do not seem to be limited to reproductive factors and remain to be understood. Women with an advantaged socioeconomic position (SEP) have a higher risk of developing breast cancer (BC) compared to their disadvantaged counterparts [1, 2]. The few studies that have considered health behaviours or anthropometric factors have shown that women with higher early life SEP had a higher risk of BC, partly mediated by age at first childbirth and the number of children but not by health behaviours [9]. Several studies suggest that screening could act as a mediator in the association between SEP and the risk of BC [8, 12, 16, 17]
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