Hormone-related Risk Factors and Postmenopausal Breast Cancer Among Nulliparous Versus Parous Women: An Aggregated Study

摘要

Nulliparity is an established breast cancer risk factor, particularly when compared with parity at young ages. Thenauthors aggregated data from 4 US prospective studies (1979–2006) including 32,641 nulliparous (1,612 breastncancers) and 204,270 parous (8,180 breast cancers) women to examine the hypothesis that nulliparity may in-ncrease susceptibility to established postmenopausal breast cancer risk factors. The aggregated hazard ratio fornnulliparous versus all parous women ¼ 1.27 (95% confidence interval: 1.21, 1.34), and that for nulliparous versusnwomen <25 years of age at first birth ¼ 1.38 (95% confidence interval: 1.30, 1.46). Among nulliparous women, thenhazard ratios for current menopausal hormone therapy use (vs. never use), body mass index u000130 kg/m2n(vs. <25nkg/m2n), and weekly consumption of u00017 alcoholic drinks (vs. none) ranged from 1.3 to 1.6. The hazard ratios did notndiffer by parity. In a model including all women, the joint association for each of these factors and nulliparityncombined compared with first birth before age 25 years was an approximately 2-fold increased breast cancer risk.nAlthough the baseline risk is higher for nulliparous women compared with parous women, these results suggestnthat the associations between hormone-related factors and breast cancer do not differ by parity.