estrogen blocker
Meaning of estrogen blocker: A loose label stretched across two unrelated drug strategies: occupying the receptor, or shutting off the supply of the hormone upstream.
Definition of estrogen blocker
An estrogen blocker is a drug that stops estrogen acting on cells. Strictly the phrase means a compound that occupies the estrogen receptor so the hormone cannot reach it, but it is applied loosely to drugs that cut estrogen production instead. Both approaches are used against breast cancers whose growth depends on the hormone, and they are not interchangeable.
What are the two strategies?
| Approach | What the drug does | Effect on hormone levels |
|---|---|---|
| Receptor modulator | Sits in the receptor in place of estrogen | Levels unchanged |
| Receptor degrader | Binds the receptor and destroys it | Levels unchanged |
| Aromatase inhibitor | Blocks the enzyme that builds estrogen | Levels fall sharply |
| Ovarian suppression | Silences the ovary's hormone output | Levels fall sharply |
Only the first two are blockers in any literal sense. The others leave the estrogen receptor free and simply starve it of anything to bind, which is a different mechanism with different consequences.
Why is blocker a poor word for some of them?
Because one whole class behaves as a blocker in some tissues and as an imitator of the hormone in others. A selective estrogen receptor modulator shuts estrogen signaling down in breast tissue while producing an estrogen-like effect on bone, where that is welcome, and on the lining of the uterus, where it is not. The tissue-by-tissue split explains why one drug can protect the skeleton and raise the risk of a uterine tumor at the same time, something the plain word blocker gives no hint of.
Which drugs suit which situation?
The choice rests first on whether the tumor carries the receptor at all, since none of these drugs does anything to a tumor reported as estrogen receptor positive in name only. It then rests on where the hormone is coming from. In women still producing estrogen from the ovaries, an aromatase inhibitor alone is ineffective and can even prompt the ovary to work harder, so it is either avoided or paired with ovarian suppression. After the ovaries stop, the remaining estrogen is built in fat and other tissue by the enzyme those drugs block, and they come into their own.
Also known as
Used in a sentence
An estrogen blocker was started once the tumor was reported as hormone receptor positive.
Good to know
Drugs described as estrogen blockers act by two unrelated routes, and one class, the selective estrogen receptor modulators, blocks the hormone in breast tissue while imitating it in the uterus and the skeleton.