Hormonal therapy medicines treat hormone-receptor-positive breast cancers in two ways. One is by lowering the amount of the hormone estrogen in the body. And the other is by blocking the action of estrogen on breast cancer cells. Most of the estrogen in women’s bodies is made by the ovaries. Estrogen makes hormone-receptor-positive breast cancers grow. So reducing the amount of estrogen or blocking its action can reduce the risk of early-stage hormone-receptor-positive breast cancers coming back or recurring after surgery. Hormonal therapy medicines can also be used to help shrink or slow the growth of advanced-stage or metastatic hormone-receptor-positive breast cancers. There are several types of hormonal therapy medicines, including aromatase inhibitors, selective estrogen receptor modulators, and estrogen receptor down-regulators.