Estrogen and progesterone are naturally occurring hormones. Given to women to treat the symptoms of menopause, they have been linked to increased risk of breast cancer.
Estrogen may also increase the risk of endometrial cancer, but progesterone helps protect against this increased risk. Estrogen and progestin (a synthetic form of progesterone) taken together are associated with increased risks of breast cancer, heart disease, stroke, and blood clots. Women who take oral contraceptives, which contain both estrogen and progestin, may have increases in early-onset breast cancers and liver cancer, but have substantially reduced risks of endometrial and ovarian cancers.