Selective Estrogen Receptor Modulators
SERMs for short
SERMs, or selective estrogen-receptor modulators, block the action of
estrogen in the breast and certain other tissues by occupying estrogen receptors
With a SERM sitting in the estrogen receptor, there is no place for the real
estrogen to "sit down"ï¿½like a game of musical chairs. The SERM blocks the more
powerful estrogen signals from getting into the estrogen receptor and telling
the cell to grow and spread.
SERMs do not affect all estrogen receptors in the same way, because, as the
name states, they are "selective":
- SERMs block (or selectively inhibit) estrogen receptors in breast cells.
Therefore, cells don't get the signals they need to grow and multiply.
- SERMs stimulate estrogen receptors in other organs, with good and bad
results. For example, the SERM tamoxifen
- stimulates liver cells, lowering cholesterol levels.
- stimulates bone cells, resulting in stronger bones and reduced risk of
- stimulates growth of uterine cells (cells in the uterus), slightly
increasing the risk of uterine cancer.
A SERM may also weakly stop the formation of new blood vessels that supply
the nutrients the cancer needs to grow. (This is called an "anti-angiogenic"
effect.) Although this action would never be enough to stop making all new blood
vessels, it may starve some cancer cells, which need extra blood vessels to
As long as a SERM is sitting inside all the estrogen receptors, the cancer
cells remain quiet and relatively harmless. After a long period of not being
stimulated, the cancer cells may die off. SERMs may even cause breast cancer
cells to destroy themselves, a process called "apoptosis," or programmed cell
There are three SERMs, each usually taken once a day by pill:
- The most prescribed SERM is tamoxifen (the brand name is Nolvadex, but
it's also now a generic drug called tamoxifen citrate).
- Raloxifene (brand name: Evista) hasn't been used to treat women with
breast cancer. But it does lower the risk of breast cancer in women who take
it to treat osteoporosis. An ongoing study in women who are at high risk for
breast cancer but have no personal history of the disease is comparing how
well tamoxifen and raloxifene reduce the risk of breast cancer.
- The third SERM, toremifene (brand name: Fareston), is relatively new and
not often used in the United States.
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