- New evidence on hormones and breast cancer risk clarifies associations with endogenous hormones, oral contraception, intrauterine devices (IUDs), parity, and lactation.
- Data have shown that estrogens, testosterone, and insulin-like growth factor I (IGF-1) are associated with a modest increased risk for breast cancer in premenopausal women.
- New data show anti-Müllerian hormone (AMH) is also associated with breast cancer risk in premenopausal women to a similar extent as other hormones.
- Data have clearly established that testosterone, prolactin, and estrogens have a positive association with breast cancer in postmenopausal women.
- Combining genetic risk score, mammography density, and plasma hormone levels significantly improves breast cancer risk prediction models, such as the National Cancer Institute’s Gail model and the Rosner-Colditz model.
- New data on oral contraception confirm older findings of modestly increased breast cancer risk, with slightly less long-term attenuation after longer duration of use than previously seen.
- Limited data on hormonal IUDs show modest positive or null association with breast cancer risk, with less data on influence of duration of use.
- Regarding established association between parity and breast cancer risk: increasing parity is associated with decreasing risk for ER+ breast cancer, but increasing risk for ER– breast cancer
- New evidence on lactation indicates increased lactation reduces risk for ER– disease.