Selective estrogen receptor modulators (SERMs)

Selective estrogen response modulators (SERMs) are hormonal therapy medicines that attach to estrogen receptors on cell surfaces.

• In normal cells, estrogen attaches to these receptors and helps regulate cell growth and other cell functions.
• In hormone receptor-positive breast cancer cells, estrogen attaches to the receptors and signals the cancer cells to grow and multiply.

When SERMs attach to estrogen receptors in breast cancer cells, they block estrogen from helping the breast cancer to grow.

Some SERMS can also lower the risk of a first-time breast cancer by blocking the effects of estrogen on normal breast tissue.

How SERMs work

SERMs work by attaching to estrogen receptors on breast cancer cells. This blocks the hormone estrogen from fueling the cells’ growth. As a result, SERMs can:

• Slow or stop breast cancer growth in any stage of breast cancer
• Lower the risk of recurrence (cancer coming back) in early-stage breast cancer

Some SERMs can block the effects of estrogen on normal breast tissue. For people at high risk of developing breast cancer, SERMs can lower cancer risk.

Because they work by attaching to estrogen receptors, SERMs can have pro-estrogen effects in other parts of the body. For example:

• They can strengthen bones in women who are postmenopausal.
• Some SERMS can stimulate cell growth in the lining of the uterus. This leads to a slight increase in the risk of uterine cancer.

SERM side effects

Common side effects of SERMs can include:

• Menopausal symptoms, such as hot flashes, night sweats, and vaginal dryness and irritation
• Vaginal discharge
• Irregular periods or vaginal bleeding
• Loss of sex drive
• Joint or bone pain

SERMs used in breast cancer treatment and risk reduction

The following SERMs are used to treat and/or reduce the risk of breast cancer.

Tamoxifen

Who can take it: Tamoxifen can be used to treat any stage of breast cancer and reduce the risk of developing cancer in the other breast. It can treat breast cancer in women and men.

Tamoxifen also can be given to lower the risk of a first-time breast cancer.

How it’s given: Tamoxifen is available as a pill and in liquid form (brand name Soltamox).

Side effects: Tamoxifen shares many of the same side effects as other SERMs. Rare but serious side effects specific to tamoxifen can include:

• Blood clots in the legs or lungs
• Stroke (caused by a blood clot cutting off the supply of blood to the brain)
• Some bone thinning in premenopausal women
• Bone strengthening in postmenopausal women
• Eye problems, such as cataracts (clouding of the lens of the eye)

A very small increased risk of endometrial cancer (cancer of the lining of the uterus) or uterine sarcoma, a rare cancer that starts in the muscle wall of the uterus

For more detailed information, visit the Tamoxifen page.

Raloxifene (Evista)

Who can take it: Raloxifene is used to reduce the risk of breast cancer in postmenopausal women at high risk. It also can be given to prevent and treat osteoporosis (thinning and weakening of the bones) in postmenopausal women.

How it's given: Raloxifene is taken by mouth, as a pill.

Side effects: Raloxifene shares side effects common to all SERMs, including hot flashes, vaginal dryness, and joint pain. Raloxifene can also:

• Strengthen bones
• Lower cholesterol levels—both total cholesterol and LDL, or “bad” cholesterol

Like tamoxifen, raloxifene can cause blood clots and increase the risk of cancers in the uterus. However, these risks are lower than they are with tamoxifen.