Exogenous Hormones and Breast Cancer Risk: Contraception, Menopausal Hormone Therapy, and Breast Cancer Survivors.

The use of exogenous estrogen and progesterone/progestin medications spans the reproductive and postreproductive lives of millions of women providing control over pregnancy timing, management of premenopausal and postmenopausal symptoms, and prevention of disease, including endometrial and ovarian cancer. These same hormones can also increase the risk of breast cancer in some settings and their use in breast cancer survivors may increase the risk of breast cancer recurrence. Given both the benefits and risks of these exogenous hormones, a detailed understanding of the available scientific evidence is imperative to help counsel individuals in their use across various settings.