Hormone therapy for breast cancer

Hormone therapy is another form of systemic therapy. It is most often used to help reduce the risk of the cancer coming back after surgery, but it may also be used for breast cancer that has spread or come back after treatment.

The female hormone estrogen promotes the growth of breast cancer cells in some women (those who have hormone receptor-positive cancers). For these women, there are ways to block the effect of estrogen or lower its levels in order to treat breast cancer.

Drugs used to block estrogen

Tamoxifen and toremifene (Fareston^®): Drugs like tamoxifen can be given to block estrogen. Tamoxifen is taken in pill or liquid form, every day for up to 10 years after surgery, to reduce the risk the cancer will come back. This drug helps women with early breast cancer if their cancer has hormone receptors (is ER-positive or PR-positive). It is also used to treat hormone receptor-positive breast cancer that has spread and to reduce the risk of breast cancer in women who are at high risk.

This drug has side effects. The most common ones are tiredness, hot flashes, vaginal discharge, and mood swings. There is also a small increase of early stage cancer of the lining of the uterus among women taking tamoxifen. But this cancer is usually found at a very early stage and is almost always cured by surgery. If you are taking tamoxifen and have any unusual vaginal bleeding you should tell your doctor right away. Blood clots are another possible side effect of tamoxifen. Still, for almost all women with breast cancer, the benefits of tamoxifen far outweigh the risks.

Toremifene works like tamoxifen, but is not used as often and is only approved for patients with metastatic breast cancer. The side effects of these drugs are similar.

Fulvestrant: Fulvestrant (Faslodex^®) is a drug that blocks the estrogen receptor and then also eliminates it temporarily. It often works even if the breast cancer is no longer responding to tamoxifen. It is given as a shot once a month. Hot flashes, mild nausea, and tiredness are the major side effects. Right now it is only approved to treat postmenopausal women with advanced breast cancer who no longer respond to tamoxifen or toremifene.

Drugs used to change hormone levels

Aromatase inhibitors (AIs): These are drugs that stop the body from making estrogen. They only work for women who are past menopause and whose cancers are hormone-receptor positive. These drugs may be used after, or even instead of tamoxifen to reduce the chance of the breast cancer coming back. These drugs are taken daily as pills.

For women after menopause, most doctors now recommend using an AI at some point during adjuvant therapy. But it’s not yet clear if starting adjuvant therapy with one of these drugs is better than giving tamoxifen and then switching to an AI. And if tamoxifen is given first, it's not clear how long it should be given. The best length of treatment with AIs is not clear. Studies now being done should help answer these questions.

These drugs don’t cause uterine cancer and very rarely cause blood clots. But they can cause bone thinning and fractures because they remove estrogens from the body. The most common side effect of AIs is joint stiffness and/or pain — like the feeling of having arthritis in many different joints at one time. This side effect may improve by switching to a different AI, but it has led some women to stop drug treatment. If this occurs, most doctors recommend using tamoxifen to complete 5 years of hormone treatment.

Surgery to change hormone levels

Removing the ovaries (ovarian ablation): In pre-menopausal women, the ovaries are the main source of estrogens. Removing them or shutting them down takes away almost all the estrogen and makes the woman post-menopausal. This may allow some other hormone therapies to work better. Ovarian ablation can be done permanently by taking out the ovaries in surgery. It also can be done with drugs. Both of these methods can cause a woman to have symptoms of menopause, including hot flashes, night sweats, vaginal dryness, and mood swings.

Other types of hormone treatment

Megestrol acetate (Megace^®) is a progesterone-like drug used as a hormone treatment for advanced breast cancer, mostly for women whose cancers do not respond to the other hormone treatments. Its major side effect is weight gain, and it is sometimes used in higher doses to reverse weight loss in patients with advanced cancer. This is an older drug that is no longer used very often.

Androgens (male hormones) may be used after other hormone treatments for advanced breast cancer have been tried. They sometimes work, but they can cause women to develop male traits, like an increase in body hair and a deeper voice.

Another option that may be tried when the cancer is no longer responding to other hormone drugs is giving high doses of estrogen. The main risk is of serious blood clots. Patients also have trouble with nausea.