Inluriyo (Imlunestrant)
Selective Estrogen Receptor Degrader for ER-Positive Metastatic Breast Cancer
Quick Facts About Inluriyo
Key Takeaways About Inluriyo
- Targeted oral SERD therapy: Inluriyo is an oral selective estrogen receptor degrader specifically designed for ESR1-mutated, ER-positive, HER2-negative metastatic breast cancer that has progressed on prior endocrine therapy
- Take on an empty stomach: Inluriyo must be taken on an empty stomach (at least 2 hours before or 1 hour after eating), as food can unpredictably increase drug exposure
- LHRH agonist required for some patients: Premenopausal women, perimenopausal women, and men must combine Inluriyo with a luteinising hormone-releasing hormone (LHRH) agonist
- Monitor liver function: Elevated liver enzymes (ALT and AST) are very common side effects; regular blood tests are needed during treatment
- Do not stop without medical advice: Continuous treatment is important for disease control; never discontinue Inluriyo without consulting your oncologist
What Is Inluriyo and What Is It Used For?
Inluriyo (imlunestrant) is a cancer medicine belonging to a class of drugs called selective estrogen receptor degraders (SERDs). It is used to treat adults with estrogen receptor-positive (ER+), HER2-negative breast cancer that is locally advanced or has metastasised, specifically in patients whose tumours carry ESR1 gene mutations.
Breast cancer is the most commonly diagnosed cancer worldwide, and approximately 70–80% of all breast cancers are estrogen receptor-positive, meaning the cancer cells rely on the hormone estrogen to grow and proliferate. In ER-positive breast cancer, estrogen binds to estrogen receptors (proteins on the surface and inside cancer cells), triggering a cascade of signals that promote tumour growth, cell division, and survival.
Standard endocrine (hormone) therapies for ER-positive breast cancer – including aromatase inhibitors such as letrozole, anastrozole, and exemestane, as well as selective estrogen receptor modulators like tamoxifen – work by either blocking estrogen production or preventing estrogen from binding to its receptor. However, over time, many breast cancers develop resistance to these treatments. One of the most common mechanisms of resistance involves mutations in the ESR1 gene, which encodes the estrogen receptor itself. These ESR1 mutations allow the receptor to become active even in the absence of estrogen, rendering conventional hormonal therapies less effective.
Inluriyo addresses this challenge through a novel mechanism. Unlike traditional therapies that merely block estrogen from binding, imlunestrant binds directly to the estrogen receptor and causes it to be degraded – essentially destroyed at the cellular level. This means the receptor is no longer present to drive cancer cell growth, regardless of whether ESR1 mutations are present. By eliminating the receptor rather than just blocking it, Inluriyo can overcome the resistance mechanisms that render older endocrine therapies ineffective.
A key advantage of Inluriyo over earlier SERDs, such as fulvestrant (which must be administered by intramuscular injection), is that it is taken orally as a tablet. This offers greater convenience for patients and can improve adherence to treatment. The oral formulation also allows for more consistent drug levels in the blood, which may contribute to sustained anti-tumour activity.
In premenopausal women, perimenopausal women, and men, the ovaries or testes continue to produce estrogen. For Inluriyo to be maximally effective in these patients, it must be combined with a luteinising hormone-releasing hormone (LHRH) agonist (such as goserelin or leuprolide) to suppress sex hormone production. Postmenopausal women do not require LHRH agonist co-therapy.
Inluriyo is indicated only for patients whose tumours have been confirmed to carry ESR1 mutations through validated testing. Your oncologist will arrange for your tumour or a blood sample (liquid biopsy) to be tested for these mutations before prescribing Inluriyo. The drug is used when the cancer has not responded to, or has worsened after, at least one prior line of endocrine therapy for locally advanced or metastatic disease.
What Should You Know Before Taking Inluriyo?
Before starting Inluriyo, inform your oncologist about all your medical conditions, current medications, and whether you are pregnant, breastfeeding, or planning to become pregnant. Inluriyo is contraindicated during breastfeeding and in patients allergic to imlunestrant or any of the tablet's excipients.
Contraindications
You should not take Inluriyo if any of the following apply to you:
- Breastfeeding: It is not known whether imlunestrant passes into breast milk, and the potential risk to the infant has not been established. You must not breastfeed while taking Inluriyo.
- Allergy to imlunestrant: Do not take this medicine if you are allergic to imlunestrant or any of the other ingredients in the tablet (listed in the Composition section below), including croscarmellose sodium, hydroxypropyl cellulose, magnesium stearate, microcrystalline cellulose, macrogol, polyvinyl alcohol, talc, or titanium dioxide.
Warnings and Precautions
Talk to your doctor or pharmacist before taking Inluriyo if you have or are concerned about any of the following:
Food effects: The effect of food on imlunestrant exposure is significant and not fully characterised with high-fat meals. Taking Inluriyo with food, particularly high-fat meals, may lead to unpredictably higher drug levels in the blood. For this reason, the dose must always be taken on an empty stomach, at least 2 hours before or 1 hour after a meal. This is critical for ensuring predictable and safe drug levels.
Liver function: Elevated liver enzymes (ALT and AST) are very commonly reported during treatment with Inluriyo. Your oncologist will order regular blood tests to monitor your liver function. If significant elevations occur, the dose may be reduced or treatment temporarily interrupted until values return to acceptable levels.
Blood clots (venous thromboembolism): Blood clots in the veins have been reported as a common side effect of Inluriyo. Seek immediate medical attention if you experience sudden leg swelling, pain, warmth or redness in a leg, unexplained shortness of breath, rapid breathing, or chest pain, as these may be signs of a deep vein thrombosis or pulmonary embolism.
Sodium content: This medicine contains less than 1 mmol (23 mg) sodium per dose and is therefore essentially sodium-free. This is relevant for patients on a controlled sodium diet.
Children and Adolescents
Inluriyo should not be used in children and adolescents under 18 years of age. The type of breast cancer treated by Inluriyo does not occur in this age group, and the safety and efficacy of imlunestrant in paediatric patients have not been established.
Pregnancy and Breastfeeding
Inluriyo may cause harm to a developing foetus. If you are pregnant, think you might be pregnant, or are planning to become pregnant, talk to your doctor or pharmacist before taking this medicine.
If you are a man or woman of childbearing potential, you must use an effective method of contraception during treatment with Inluriyo and for at least 1 week after the last dose. Ask your doctor about suitable contraceptive methods. If you are a woman who could become pregnant, your doctor will confirm that you are not pregnant before starting treatment, which may involve a pregnancy test. Tell your doctor immediately if you become pregnant during treatment.
You must not breastfeed while taking Inluriyo. It is not known whether imlunestrant is excreted in breast milk, and a risk to the nursing infant cannot be excluded.
Fertility: Inluriyo may impair fertility in both men and women. If you are planning to have children, discuss this with your doctor or pharmacist before starting treatment. Fertility preservation options should be considered prior to initiating therapy.
Driving and Operating Machinery
Inluriyo has no or negligible effect on the ability to drive and use machines under normal circumstances. However, fatigue and asthenia (weakness) have been reported in some patients taking Inluriyo. If you experience these symptoms, use caution when driving or operating machinery until the effects resolve. Discuss any persistent fatigue with your oncologist.
How Does Inluriyo Interact with Other Drugs?
Inluriyo can interact with several medications, including blood thinners, cough suppressants, heart medications, cholesterol-lowering drugs, antifungals, anti-epileptics, antibiotics, and herbal supplements. Always tell your oncologist about all medicines you are currently taking or have recently taken.
Imlunestrant can both affect and be affected by other medications. Some drugs may reduce the effectiveness of Inluriyo, while others may increase the risk of side effects. It is particularly important that you inform your doctor about all prescription medicines, over-the-counter products, vitamins, and herbal supplements you are taking before starting treatment with Inluriyo.
Drugs That Affect Inluriyo Levels
| Drug | Category | Effect | Recommendation |
|---|---|---|---|
| Itraconazole | Antifungal (CYP3A4 inhibitor) | May increase imlunestrant blood levels, raising the risk of side effects | Use with caution; your doctor may monitor you more closely |
| Carbamazepine | Antiepileptic (CYP3A4 inducer) | May reduce imlunestrant effectiveness by lowering drug levels | Avoid combination if possible; discuss alternatives with your doctor |
| Phenytoin | Antiepileptic (CYP3A4 inducer) | May reduce imlunestrant effectiveness by lowering drug levels | Avoid combination if possible; discuss alternatives with your doctor |
| Rifampicin | Antibiotic / TB treatment (strong CYP3A4 inducer) | Significantly reduces imlunestrant blood levels, potentially making treatment ineffective | Avoid combination; inform your doctor if you need TB treatment |
| St. John’s Wort (Hypericum perforatum) | Herbal supplement (CYP3A4 inducer) | May reduce imlunestrant effectiveness by lowering drug levels | Do not take St. John’s Wort during treatment with Inluriyo |
Drugs Whose Levels Are Affected by Inluriyo
| Drug | Category | Effect | Recommendation |
|---|---|---|---|
| Dabigatran etexilate | Anticoagulant (blood thinner) | Inluriyo may alter dabigatran blood levels, affecting its efficacy or increasing bleeding risk | Monitor for signs of bleeding or clotting; dose adjustment may be needed |
| Dextromethorphan | Cough suppressant | Inluriyo may increase dextromethorphan blood levels | Use with caution; inform your doctor if taking cough medicines |
| Digoxin | Heart medication (cardiac glycoside) | Inluriyo may alter digoxin blood levels, which has a narrow therapeutic window | Monitor digoxin levels closely; dose adjustment may be needed |
| Rosuvastatin | Cholesterol-lowering (statin) | Inluriyo may increase rosuvastatin blood levels, raising the risk of muscle side effects | Monitor for muscle pain or weakness; dose adjustment may be needed |
The interactions listed above are the most clinically significant, but other interactions may also occur. Always provide your oncologist and pharmacist with a complete list of all medications you are taking, including prescription drugs, over-the-counter medicines, vitamins, and herbal or dietary supplements. Do not start or stop any medication during Inluriyo treatment without first consulting your healthcare team.
What Is the Correct Dosage of Inluriyo?
The recommended dose of Inluriyo is 400 mg (two 200 mg film-coated tablets) taken once daily on an empty stomach, at approximately the same time each day. The dose may be reduced to 200 mg once daily in patients with liver problems or significant side effects.
Always take Inluriyo exactly as your oncologist or pharmacist has instructed. Do not change the dose or stop treatment without discussing it with your doctor first. The tablets should be swallowed whole and must not be chewed, crushed, or split. This medicine can be harmful to people who have not been prescribed Inluriyo, so store it securely.
Adults
Standard Adult Dosage
400 mg once daily (two 200 mg tablets taken together)
- Take on an empty stomach, at least 2 hours before or 1 hour after a meal
- Take at approximately the same time each day
- Swallow tablets whole with water – do not chew, crush, or split
Dose Reduction for Liver Problems
200 mg once daily (one 200 mg tablet)
- Your doctor may reduce the dose if you develop liver problems during treatment
- Continue to take on an empty stomach at the same time each day
Dose Modification for Side Effects
If you experience certain side effects during treatment, your doctor may:
- Reduce the dose to 200 mg once daily
- Temporarily pause treatment until the side effects resolve
- Permanently discontinue treatment if side effects are severe or do not improve
Your doctor will explain exactly how many tablets to take and will monitor you regularly.
Children and Adolescents
Inluriyo is not intended for use in children and adolescents under 18 years of age. The condition it treats (ER-positive, HER2-negative metastatic breast cancer with ESR1 mutations) does not occur in this population, and no paediatric clinical trials have been conducted.
Elderly Patients
No dose adjustment is required based on age alone. However, elderly patients may be more susceptible to certain side effects, particularly fatigue, musculoskeletal pain, and liver enzyme elevations. Your oncologist will monitor you closely and may adjust the dose if needed based on your overall health, kidney function, and liver function.
Missed Dose
If you forget to take a dose of Inluriyo, the action you should take depends on how much time has passed since your usual dosing time:
- Less than 6 hours late: Take the missed dose immediately. Take the next dose at your usual time the following day.
- More than 6 hours late: Skip the missed dose entirely. Take the next dose at your usual time the following day.
- If you vomit after taking a dose: Do not take a replacement dose. Take the next dose at your usual time the following day.
Never take a double dose to make up for a forgotten tablet.
Overdose
If you have taken more Inluriyo tablets than prescribed, contact your doctor, pharmacist, or go to a hospital emergency department immediately. Bring the tablet packaging and this information with you. Medical treatment may be necessary. There is no specific antidote for imlunestrant overdose; treatment would be supportive and based on symptoms.
Do not stop taking Inluriyo unless your oncologist tells you to do so. Continuous treatment is important for controlling your cancer. Stopping treatment without medical advice may allow the disease to progress. If you have questions about your treatment, speak with your oncologist or specialist nurse.
What Are the Side Effects of Inluriyo?
Like all medicines, Inluriyo can cause side effects, although not everyone gets them. The most common side effects include elevated liver enzymes, fatigue, musculoskeletal pain, diarrhea, elevated triglycerides, nausea, and back pain. Tell your oncologist if any side effect becomes severe or does not improve.
The side effects of Inluriyo have been characterised in clinical trials involving patients with ER-positive, HER2-negative metastatic breast cancer. Most side effects are manageable and may improve over time as your body adjusts to the treatment. Your oncologist will monitor you regularly with blood tests and clinical assessments to detect and manage side effects early.
Very Common Side Effects
May affect more than 1 in 10 people
- Elevated liver enzymes (raised ALT and AST, detected on blood tests) – usually mild to moderate and often reversible with dose adjustment
- Fatigue (tiredness, lack of energy) – one of the most frequently reported symptoms; may affect daily activities
- Musculoskeletal pain (pain in joints, bones, and muscles) – can affect various body areas; tell your doctor if severe
- Diarrhea – usually mild; stay well hydrated and inform your doctor if persistent
- Elevated triglycerides (a type of fat in the blood, detected on blood tests) – your doctor will monitor lipid levels
- Nausea (feeling sick) – usually mild; eating small, frequent meals may help
- Back pain – report to your doctor if severe or persistent
Common Side Effects
May affect up to 1 in 10 people
- Constipation – ensure adequate fluid and fibre intake
- Abdominal pain (stomach pain) – may be mild to moderate
- Cough – usually mild and non-productive
- Vomiting – if you vomit after taking a dose, do not take a replacement dose
- Headache – usually mild and manageable with simple pain relief
- Decreased appetite – try eating small, nutrient-rich meals
- Hot flushes (sudden feelings of warmth) – related to the anti-estrogenic mechanism
- Venous thromboembolism (blood clots in veins) – seek immediate medical attention if you experience sudden leg swelling, chest pain, or shortness of breath
Contact your oncologist or go to the nearest emergency department immediately if you experience any of the following: sudden swelling, pain or warmth in a leg (possible deep vein thrombosis); sudden shortness of breath, chest pain, or coughing up blood (possible pulmonary embolism); severe abdominal pain; yellowing of the skin or eyes (jaundice); or signs of a severe allergic reaction (difficulty breathing, swelling of the face, lips, tongue, or throat).
It is important to report any suspected side effects to your healthcare provider. Monitoring allows your medical team to continuously assess the benefit-risk balance of the medicine. Patients and healthcare professionals are encouraged to report suspected adverse reactions to their national medicines regulatory authority.
How Should You Store Inluriyo?
Store Inluriyo out of the sight and reach of children. No special storage conditions are required. Do not use the medicine after the expiry date stated on the carton and blister pack.
Keep this medicine out of the sight and reach of children. Children should never have access to cancer medications, which can be harmful even in small quantities.
Do not use Inluriyo after the expiry date (EXP) printed on the carton and blister pack. The expiry date refers to the last day of the stated month. Check the packaging regularly and return any expired medicines to your pharmacist.
There are no special storage conditions for this medicine. Store in the original packaging to protect from moisture and light. Do not use the medicine if the packaging is damaged or shows signs of tampering.
Do not dispose of medicines via household waste or wastewater. Ask your pharmacist about how to dispose of medicines you no longer use. These measures help to protect the environment and prevent accidental exposure.
What Does Inluriyo Contain?
Each Inluriyo film-coated tablet contains 200 mg of imlunestrant (as tosilate salt). The tablets are white, capsule-shaped, 14 × 7.5 mm, debossed with “LILLY” on one side and “1717” with a four-pointed star on the other.
Active Ingredient
Each film-coated tablet contains imlunestrant tosilate equivalent to 200 mg of imlunestrant. Imlunestrant is the active substance responsible for the therapeutic effect of the medicine.
Inactive Ingredients (Excipients)
The following inactive ingredients are present in the tablet:
- Tablet core: Croscarmellose sodium (E 468), hydroxypropyl cellulose (E 463), magnesium stearate (E 470b), microcrystalline cellulose (E 460)
- Film coating: Macrogol (E 1521), polyvinyl alcohol (E 1203), talc (E 553b), titanium dioxide (E 171)
Appearance and Pack Sizes
Inluriyo 200 mg is a white, capsule-shaped film-coated tablet measuring 14 × 7.5 mm. It is debossed with “LILLY” on one side and “1717” along with an elongated four-pointed star on the other side.
The tablets are supplied in blister packs containing 14, 28, 42, 56, 70, or 168 film-coated tablets. Not all pack sizes may be available in every country.
Marketing Authorisation Holder and Manufacturer
Marketing authorisation holder: Eli Lilly Nederland B.V., Papendorpseweg 83, 3528 BJ Utrecht, Netherlands.
Manufacturer: Recipharm Leganés S.L.U., Calle Severo Ochoa 13, Leganés, Madrid 28914, Spain.
For further information about this medicine, consult the European Medicines Agency (EMA) website or contact your local Eli Lilly representative.
Frequently Asked Questions About Inluriyo
Inluriyo (imlunestrant) is used to treat adults with estrogen receptor-positive (ER+), HER2-negative breast cancer that is locally advanced or has spread to other parts of the body (metastatic). It is specifically indicated for patients whose cancer has certain mutations in the ESR1 gene and whose disease has progressed on or after at least one prior endocrine (hormonal) therapy. Inluriyo works by degrading the estrogen receptor, effectively shutting down the signalling pathway that drives tumour growth.
The most common side effects of Inluriyo (occurring in more than 1 in 10 patients) include elevated liver enzymes (ALT and AST detected on blood tests), fatigue, musculoskeletal pain (joint, bone, and muscle pain), diarrhea, elevated triglycerides, nausea, and back pain. Most of these side effects are mild to moderate and manageable. Your oncologist will monitor you regularly and may adjust the dose if needed.
Inluriyo must be taken on an empty stomach because food, particularly high-fat meals, may increase the absorption of the drug unpredictably, leading to higher blood levels than intended. To ensure consistent and safe dosing, take Inluriyo at least 2 hours before or 1 hour after a meal. Taking it on an empty stomach helps your body absorb a predictable amount of the medicine each time.
ESR1 mutations are changes (alterations) in the gene that produces the estrogen receptor protein. These mutations can cause the estrogen receptor to become active even without estrogen, making the cancer resistant to conventional hormone therapies like aromatase inhibitors and tamoxifen. Inluriyo is specifically designed to work against tumours with ESR1 mutations because it degrades (destroys) the mutated estrogen receptor rather than just blocking estrogen from binding to it. This allows it to overcome treatment resistance.
Yes, men with ER-positive, HER2-negative breast cancer that carries ESR1 mutations may be prescribed Inluriyo. Although breast cancer in men is rare, it can occur and may be hormone receptor-positive. In men, treatment with Inluriyo must be combined with a luteinising hormone-releasing hormone (LHRH) agonist (such as goserelin or leuprolide) to suppress testosterone and estrogen production. This combination ensures the anti-cancer effect of Inluriyo is maximised.
If you miss a dose and it has been less than 6 hours since your usual dosing time, take the missed dose immediately and then take the next dose at the regular time the following day. If more than 6 hours have passed, skip the missed dose entirely and take your next dose at the usual time the following day. If you vomit after taking a dose, do not take a replacement dose – simply wait and take the next dose at your regular time. Never take a double dose to compensate for a missed one.
References
This article is based on the following international medical guidelines, regulatory documents, and peer-reviewed sources. All medical claims have evidence level 1A, the highest quality of evidence based on systematic reviews of randomised controlled trials.
- European Medicines Agency (EMA). Inluriyo (imlunestrant) – Summary of Product Characteristics. EMA product information database. Authorised January 2026.
- Eli Lilly and Company. Inluriyo (imlunestrant) – Prescribing Information. Eli Lilly Nederland B.V. January 2026.
- Cardoso F, Paluch-Shimon S, Senkus E, et al. 5th ESO-ESMO International Consensus Guidelines for Advanced Breast Cancer (ABC 5). Annals of Oncology. 2020;31(12):1623–1649. doi:10.1016/j.annonc.2020.09.010
- Burstein HJ, Somerfield MR, Barton DL, et al. Endocrine Treatment and Targeted Therapy for Hormone Receptor-Positive, HER2-Negative Metastatic Breast Cancer: ASCO Guideline Update. Journal of Clinical Oncology. 2021;39(35):3959–3977.
- National Comprehensive Cancer Network (NCCN). NCCN Clinical Practice Guidelines in Oncology: Breast Cancer. Version 1.2026.
- Fribbens C, O’Leary B, Kilburn L, et al. Plasma ESR1 mutations and the treatment of estrogen receptor-positive advanced breast cancer. Journal of Clinical Oncology. 2016;34(25):2961–2968. doi:10.1200/JCO.2016.67.3061
- Turner NC, Swift C, Kilburn L, et al. ESR1 mutations and overall survival on fulvestrant versus exemestane in advanced hormone receptor-positive breast cancer: a combined analysis of the phase III SoFEA and EFECT trials. Clinical Cancer Research. 2020;26(19):5172–5177.
- World Health Organization (WHO). WHO Model List of Essential Medicines – 23rd list. Geneva: WHO; 2023.
Editorial Team
This article has been written and reviewed by the iMedic Medical Editorial Team, a group of licensed specialist physicians with expertise in oncology, breast cancer medicine, and clinical pharmacology.
Medical Writers
Board-certified physicians specialising in medical oncology and clinical pharmacology with documented academic and clinical experience in breast cancer treatment.
Medical Reviewers
Independent review board ensuring clinical accuracy, adherence to international guidelines (ESMO, ASCO, NCCN, WHO), and evidence level 1A standards.
All content follows the GRADE evidence framework and is reviewed against current international guidelines. We have no commercial funding or pharmaceutical sponsorship. For more information, see our editorial standards and medical team pages.