Imlunestrant at a glance
Medicine class
Selective oestrogen receptor degrader (SERD).
Biomarker requirement
An activating ESR1 mutation must be confirmed using an appropriate validated test.
Administration
Take on an empty stomach. Swallow tablets whole; do not split, crush or chew them.
Key monitoring
Liver enzymes require monitoring during treatment and when clinically indicated.
What is Imlunestrant used for?
Licensed as monotherapy for:
Adults with ER-positive, HER2-negative locally advanced or metastatic breast cancer with an activating ESR1 mutation, where disease has progressed after endocrine-based treatment.
How does Imlunestrant work?
Imlunestrant binds to normal and mutant oestrogen receptor-alpha, blocks its activity and promotes its breakdown. This reduces oestrogen-dependent signalling and limits the growth of ER-positive breast cancer cells.
Imlunestrant preparations and strengths
Tablet
Route: Oral
Strengths: 200 mg
How to take Imlunestrant
Follow the oncology team's instructions. Food substantially increases imlunestrant exposure, so take it on an empty stomach. Swallow tablets whole because splitting, crushing or chewing has not been studied and could expose caregivers to the active substance.
Swallow tablets whole with water.
Do not split, crush or chew tablets.
Imlunestrant side effects
Common or expected effects
- Raised ALT or AST liver enzymes
- Fatigue or weakness
- Diarrhoea
- Nausea or vomiting
- Joint, muscle, bone or back pain
- Raised triglycerides
- Constipation or abdominal pain
- Headache, reduced appetite, cough or hot flushes
Get urgent medical advice
- Venous blood clots, potentially causing one-sided limb pain or swelling, sudden breathlessness, chest pain or coughing up blood
- Potential liver injury, particularly jaundice, dark urine or pale stools
- Severe allergic reaction with facial or throat swelling, breathing difficulty, dizziness or collapse
Imlunestrant in pregnancy
Imlunestrant should not be used during pregnancy because its mechanism and animal studies indicate a risk of fetal harm and miscarriage. Pregnancy status should be checked before treatment where relevant, and highly effective contraception is required during treatment and afterwards. Contact the oncology team promptly if pregnancy occurs.
Imlunestrant while breastfeeding
Breastfeeding is contraindicated. It is unknown whether imlunestrant or its metabolites enter human milk, and serious effects in a breastfed infant cannot be excluded.
Imlunestrant interactions
The oncology team should review prescription, non-prescription and herbal products before treatment. Important examples include:
Strong CYP3A inhibitors, including itraconazole
They can substantially increase imlunestrant exposure; concomitant use should generally be avoided or specialist-managed.
Strong CYP3A inducers, including carbamazepine, phenytoin, rifampicin and St John’s wort
They can reduce imlunestrant exposure and potentially reduce effectiveness; concomitant use should generally be avoided.
Digoxin and other sensitive P-glycoprotein substrates
Imlunestrant can increase their exposure, potentially increasing adverse effects.
Common questions about Imlunestrant
Answers are fully visible for fast scanning and source review.
What type of breast cancer is imlunestrant licensed to treat?
ER-positive, HER2-negative locally advanced or metastatic breast cancer carrying an activating ESR1 mutation after progression on endocrine-based treatment.
Why is ESR1 testing needed?
The monotherapy licence is restricted to cancers with an activating ESR1 mutation, so a validated tumour or plasma test is required.
Is imlunestrant chemotherapy?
Sources
These sources were used to prepare and review this medicine page.
Prepared and reviewed by the iatroX editorial team.