ESR1 and breast cancer: The magnitude of the protective effect from multiple full-term pregnancies for ER+PR+ breast cancer in our study is similar to that observed in a previous study of young women [21], smaller than that observed in a study of premenopausal women (OR 0.44, 95% CI 0.26 to 0.75 of ER+PR+ cancer for women having three or more live births compared with nulliparous women) [22], and greater than that in two studies of women under 45 years of age that did not find any associations with either receptor subtype [19,20].