Hormones are chemicals produced by glands in the body and are circulated in the blood. Hormone therapy -- also called hormonal therapy, hormone treatment, or endocrine therapy -- is any treatment that adds, blocks, or removes hormones. For certain conditions (such as diabetes or menopause), hormones are given to boost low hormone levels. Sometimes, hormone therapy is used to slow or stop the growth of certain cancers (such as prostate and breast cancer). The female hormones estrogen and progesterone, for example, promote the growth of some breast cancer cells. So hormone therapy may be given to block the body's naturally occurring estrogen and fight the cancer's growth. Sometimes surgery is needed to remove the source of the hormone in question -- in the case of breast cancer, the ovaries may be removed.
 

When Is It Used to Treat Breast Cancer?
Hormone therapy is used in women with breast cancer whose tumors are sensitive to the hormones estrogen or progesterone (meaning that hormones cause the cancer to grow). Not all breast cancers are hormone sensitive, so not all breast cancers will respond to a hormone-blocking treatment.

The drugs slow or stop the growth of cancer cells that are present in the body. As an adjuvant (add-on) therapy, hormone therapy helps prevent the original breast cancer from returning and also helps prevent the development of new cancers in the other breast.

Women at an increased risk of developing breast cancer (those with a genetic predisposition or family history) have the option of taking hormone therapy to reduce their chance of ever developing the disease.

What Are Common Hormone Drugs Used for Breast Cancer?

Tamoxifen.The gold standard of hormone therapy in breast cancer is tamoxifen, marketed as Nolvadex, a drug in pill form that interferes with the activity of estrogen. Known as the "antiestrogen," tamoxifen is a pill that has been used for more than 30 years to treat patients with advanced (metastatic or stage IV) breast cancer.

Tamoxifen is also used as additional therapy following surgery for early (stages I and II) and locally advanced (stage III) breast cancer and as a means of reducing the risk of ever developing breast cancer among women at particularly high risk (those with a genetic predisposition to and a family history of the disease). Tamoxifen is useful in both premenopausal and postmenopausal women.

Tamoxifen is also used to treat men with breast cancer.

Arimidex and Femara. The most well known of these drugs, Arimidex and Femara, belong to a class of medications known as aromatase inhibitors. After menopause, a woman's main source of estrogen comes through a process called aromatization, in which male hormones called androgens (produced by the adrenal glands located at the top of the kidneys) are converted into estrogen. This process takes place throughout the body, in the fatty tissue. These drugs fight tumor growth by stopping the conversion of androgens into estrogen.

Arimidex (Anastrozole is the generic name) was initially approved for the treatment of advanced (stage IV) breast cancer in women who've gone through menopause and whose cancer has grown despite taking tamoxifen. It has replaced tamoxifen as the first-line therapy for postmenopausal women with hormone-positive or hormone-unknown locally advanced (stage III) or stage IV breast cancer. It is also approved as an add-on treatment of early hormone-positive breast cancer (stages I and II) in women who are postmenopausal. It is also taken in pill form.

Femara (also called Letrozole) is approved for initial or follow-up treatment of hormone-sensitive locally advanced or metastatic breast cancer in women who have gone through menopause. It is taken in pill form, once each day.

Tamoxifen and Raloxifene (marketed as Evista) are the only drug currently approved for breast cancer prevention in high-risk women. However, studies are under way to test whether the aromatase inhibitors can also be safely used for this purpose.

What Are the Side Effects of Hormone Therapy for Breast Cancer?

The side effects of tamoxifen therapy for breast cancer are similar to symptoms of menopause. The most common side effects are hot flashes, vaginal discharge, fluid retention, and swelling. Some women experience irregular menstrual periods, headaches, fatigue, nausea and/or vomiting, vaginal dryness or itching, irritation of the skin around the vagina, and skin rash. As is the case with menopause, not all women who take tamoxifen have these symptoms. Men who take Tamoxifen may experience headaches, nausea and/or vomiting, skin rash, impotence, or a decrease in sexual interest.

There is evidence that tamoxifen therapy can increase the risk of cancer of the uterus in some women. Women taking tamoxifen should have a pelvic examination every year to look for any signs of cancer. Any vaginal bleeding, other than menstrual bleeding, should be reported to a doctor as soon as possible.

Tamoxifen therapy has been linked to an increased risk of blood clots, especially in women who are also taking chemotherapy. It can also interfere with other drugs you may be taking.

Raloxifene has similar side effects to Tamoxifen, but to a lesser extent.

For Femara, the most common side effects are mild nausea and vomiting, tiredness, headaches, muscular aches, joint pain, and hot flashes that tend to eventually diminish or disappear. Some women may notice some hair thinning, but this is usually mild and goes back to normal at the end of treatment.

For Arimidex, common side effects include hot flashes, nausea, decreased energy and weakness, back pain, bone pain, increased cough, flu-like symptoms, swelling of the arms and legs, as well as joint pain and stiffness.

Both Femara and Arimidex are linked to increased bone loss. Bone density should be monitored while taking these drugs.

There are other hormone therapy drugs used to treat breast cancer. Most, such as Aromasin, Faslodex, and Fareston are used to treat metastatic breast cancer.