[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Pharmacology](https://durgical.com/en/pharmacology/) › Selective oestrogen receptor degraders (SERDs)

# Selective oestrogen receptor degraders (SERDs)

Pure antioestrogens: they block the oestrogen receptor and make the cell destroy it. Used for hormone-receptor-positive breast cancer.

Updated Nov 1, 2026

## What they are

Drugs that bind the oestrogen receptor with no agonist activity and lower the amount of receptor in the cell. Fulvestrant, an injected steroid, was the first; elacestrant is an oral, non-steroidal SERD for tumours with ESR1 mutations.

## Mechanism of action

A SERD occupies the ligand-binding pocket of the oestrogen receptor, so oestrogen cannot bind, and leaves the receptor in a shape that the cell tags for destruction in the proteasome. With less receptor, oestrogen-dependent genes stay off. Because SERDs act directly on the receptor, they can work when aromatase inhibitors fail, including in some tumours whose receptor is switched on by an ESR1 mutation.

Target: Oestrogen receptor alpha (ERα, gene ESR1)

## Key points

- SERD = pure antagonist + receptor degradation; SERM = mixed agonist/antagonist.
- Fulvestrant is given by slow intramuscular injection into both buttocks; mind the sciatic nerve.
- Used in postmenopausal hormone-receptor-positive breast cancer, often with a CDK4/6 inhibitor.
- Fulvestrant can falsely raise estradiol immunoassays.

## Drugs in this class

- [**Fulvestrant** Pure antioestrogen given into the buttock muscle. It blocks the oestrogen receptor and makes the cell destroy it; for… Oestrogen receptor alpha (ERα), ligand-binding domain](https://durgical.com/en/pharmacology/fulvestrant/)
- [**Elacestrant** Oral oestrogen receptor antagonist of the SERD group, for advanced ER-positive, HER2-negative breast cancer with an… Oestrogen receptor alpha (ERα), ligand-binding domain](https://durgical.com/en/pharmacology/elacestrant/)

## Others in the class

- elacestrant (oral)

## Test yourself

Think of the answer, then tap the question to see it.

## What two things does a SERD do to the oestrogen receptor?

It blocks it (pure antagonist) and causes its degradation.

## Which SERD is injected and which is taken by mouth?

Fulvestrant is intramuscular; elacestrant is oral.

## Why would a SERD help when an aromatase inhibitor no longer works?

It acts on the receptor itself rather than on oestrogen production, so it can block a receptor that stays active with little oestrogen, as with some ESR1 mutations.

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Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.

Sources: [DailyMed - FULVESTRANT injection, solution](https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=0f05b699-c440-42c1-9557-46759a10ab17) (DailyMed (U.S. National Library of Medicine), 2026); [Estrogen Receptor Alpha Ligand Binding Domain in Complex with RAD1901](https://www.rcsb.org/structure/7TE7) (RCSB Protein Data Bank, 2022).

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Representative model, for educational purposes only.

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Source: https://durgical.com/en/pharmacology/classes/selective-oestrogen-receptor-degraders/
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/pharmacology/classes/selective-oestrogen-receptor-degraders/