Breast Cancer Overview

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Treating Breast Cancer TOPICS

Hormone therapy for breast cancer

Cancers that have hormone receptors in the cells (are ER-positive or PR-positive) are called hormone receptor-positive. In those cancers, the female hormone estrogen promotes the growth of the cancer. Hormone therapy for breast cancer works by blocking the effects of estrogen or lowering estrogen levels.

It can be used to help reduce the risk of the cancer coming back after surgery. It is also helpful in treating advanced breast cancer.

Drugs used to block estrogen

Tamoxifen and toremifene (Fareston®): These drugs stop estrogen from telling cells to grow and divide.

In women with early-stage breast cancer that is hormone receptor-positive, taking tamoxifen every day lowers the chance of the cancer coming back. It is taken by mouth every day for at least 5 years after surgery. Tamoxifen is also used to treat hormone receptor-positive breast cancer that has spread.

This drug has side effects. The most common ones are tiredness, hot flashes, vaginal discharge, and mood swings. More serious side effects are rare and can include uterine cancer and blood clots in the leg or lung. 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 advanced breast cancer. The side effects of these drugs are similar.

Fulvestrant: Fulvestrant (Faslodex®) is a drug that blocks the estrogen receptor and then also makes it go away for a time. It is given as a shot once a month. Hot flashes, mild nausea, and tiredness are the major side effects. It can be used to treat women with advanced breast cancer after other hormone drugs stop working.

Drugs used to change hormone levels

Aromatase inhibitors (AIs): The ovaries make most of the body’s estrogen before menopause. After menopause, a small amount of estrogen is made in fat tissue. These drugs stop the fat tissue from making estrogen. They only lower estrogen levels if the ovaries aren’t working (like after menopause). They can only be used in women who haven’t gone through menopause if a drug to turn off the ovaries (a LHRH analog, see below) is used as well. For women who have gone through menopause, AIs are the main drugs used to reduce the chance of hormone receptor-positive breast cancer from coming back. They are also used to treat advanced breast cancer. These drugs are taken daily as pills.

The most common side effects of AIs are hot flashes and muscle and/or joint pain. This muscle and joint pain sometimes gets better if you are switched to another AI. Because they remove estrogens from the body, AIs can cause bone thinning which can cause bones to break. If you can’t take AIs because of side effects, you will likely be switched to tamoxifen to complete 5 years of hormone treatment.

Luteinizing hormone-releasing hormone (LHRH) analogs: The ovaries are the main source of estrogens in women who have not gone through menopause. Drugs that shut down the ovaries lower estrogen levels. These drugs, called LHRH analogs, can be used to treat advanced hormone receptor-positive breast cancers on their own. They are more often used with other hormone therapy drugs to help them work better. They are given as injections, most often once a month. Side effects are the same as symptoms of menopause, such as hot flashes, night sweats, vaginal dryness, and mood swings.

Surgery to change hormone levels

Removing the ovaries: Surgery to remove the ovaries can be used instead of LHRH analogs to lower estrogen levels in women who have not gone through menopause.

Other types of hormone treatment

Some other drugs can be used to treat hormone receptor-positive breast cancer, but they are used rarely, if it all. They are discussed in our document Breast Cancer.

Last Medical Review: 09/09/2014
Last Revised: 09/09/2014