Higher levels of estradiol in the body are associated with an increased risk of breast cancer and uterine cancer.

Some genes promote higher growth of estrogen receptors during menopausal hormone therapy. This increases the risk of ER-positive breast cancer.

Estrogen receptor positive is the most common form of breast cancer – around 80% of breast cancers are ER-positive.

Breast cancer cells that do not have estrogen receptors are known as estrogen-receptor-negative (or ER-negative) cancers.