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What Are SERMs - Selective Estrogen-Receptor Modulators?


Updated July 02, 2008

Question: What Are SERMs - Selective Estrogen-Receptor Modulators?
After primary treatment for estrogen-receptor positive breast cancer, you may need to take a SERM to help prevent recurrence. Learn about SERMs, and their benefits and risks.
Answer: SERMs are selective estrogen-receptor modulators, or drugs that block the naturally circulating estrogen in breast tissues and other estrogen-sensitive tissues in your body. SERMs block natural estrogen by getting into the estrogen receptors before your own estrogen can get into place and signal the cells to grow and spread. If you've had estrogen-receptor positive breast cancer, your oncologist may prescribe a SERM as a follow-up treatment, taken as a daily pill for five years after primary treatment.

SERMs are called "selective" because they bind to particular estrogen receptors. This selective binding action is sometimes called estrogen inhibition, or estrogen suppression. SERMs do not prevent the production of estrogen, but they help to slow or stop the growth of estrogen-sensitive cancer cells by starving them of a full dose of natural estrogen.

These drugs, like many adjuvant breast cancer therapies, have benefits and risks. While they help prevent a recurrence of estrogen-receptor positive breast cancer, they also:

  • stimulate your liver cells, and lower your cholesterol levels
  • protect bone health for post-menopausal women, keeping bones strong and preventing breaks and fractures
On the other hand, SERMs can have undesired effects:
  • endometrical thickening, raising your risk of uterine cancer
  • menopausal symptoms (hot flashes, vaginal dryness, low libido)
Tradeoffs between the benefits and risks of SERMs must be weighed with a view to your long-term survival. Most doctors agree that the benefits outweigh the risks. SERMs are effective at preventing a relapse of estrogen-sensitive breast cancer.

There are three SERMs currently available:

  • Tamoxifen, the first SERM to be used as an anticancer drug
  • Evista (raloxifene), intended to treat osteoporosis, but effective at reducing the risk of breast cancer
  • Fareston (toremifene), which as of 2008, was just starting to be used in the U.S.

National Cancer Institute. Understanding Cancer Series: Estrogen Receptors/SERMs. Last updated: 09/01/2006.

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