Hormone therapies slow or stop the growth of hormone receptor-positive tumors by preventing the cancer cells from getting the hormones they need to grow. The hormone estrogen can play a part in stimulating some breast cancers to grow; there are a number of different hormone therapies that work in different ways to block the effect of estrogen on cancer cells. Hormone therapy is used to treat breast cancer that has come back after treatment (recurrence) or that has spread to another part of the body. Hormone therapy is often used after surgery to help reduce the risk of cancer coming back. There are several types of hormone therapy, which use different ways to keep estrogen from helping cancer grow. Most types of hormone therapy for breast cancer either lower estrogen levels or stop estrogen from acting on breast cancer cells. Hormonal therapy medicines can also be used to help shrink or slow the growth of advanced-stage or metastatic hormone-receptor-positive breast cancers. The side effects of hormone therapy depend largely on the specific drug or the type of treatment. The benefits and harms of taking hormone therapy should be carefully weighed for each woman.