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. 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. We 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. In 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. These 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.

中文翻译：

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生命周期社会经济地位和个人社会流动性对乳腺癌风险的影响

具有优越社会经济地位 (SEP) 的女性患乳腺癌 (BC) 的风险较高。这种关联的原因似乎并不限于生殖因素，仍有待了解。我们的目的是考虑一系列广泛的潜在中介因素，调查童年时期的生命全程 SEP 和社会流动性对 BC 风险的影响。我们在两个欧洲前瞻性队列 E3N (N = 83,436) 和 EPIC-Italy (N = 20,530) 中使用了发现-复制策略。在 E3N 中，7877 名女性在平均 24.4 年的随访期间被诊断出患有 BC，而在 EPIC-Italy 中，893 名 BC 病例在 15.1 年内被诊断出。使用 Cox 比例风险模型对估算数据进行风险比 (HR) 估计。在 E3N 中，受过高等教育的女性患 BC 的风险较高（HR [95%CI] = 1.21 [1.12, 1.30]）。通过调整生殖因素，特别是首次分娩的年龄，这种关联性被减弱（HR[95%CI] = 1.13 [1.04, 1.22]）。健康行为、人体测量变量和 BC 筛查对这种关联的影响较弱。保持稳定优势 SEP 的女性患 BC 的风险较高（HR [95%CI] = 1.24 [1.07; 1.43]），在调整潜在中介因素后减弱（HR [95%CI] = 1.13 [0.98; 1.31]） 。这些结果在 EPIC-Italy 中得到了重复。这些结果证实了生殖因素在 BC 风险的社会梯度中的重要作用，而这一点似乎并没有被包括癌症筛查在内的大量潜在中介因素完全解释，这表明需要进一步研究来确定其他机制。