FDA Approves Imlunestrant (Inluriyo) for Certain Hormone Receptor-Positive Breast Cancers

On Sept. 25, 2025, the U.S. Food and Drug Administration (FDA) approved imlunestrant (brand name: Inluriyo) to treat adults diagnosed with estrogen receptor-positive, HER2-negative advanced-stage or metastatic breast cancer with an ESR1 mutation that grew during or after being treated with another type of hormonal therapy.

Imlunestrant is a selective estrogen receptor downregulator (SERD), a type of hormonal therapy.

The FDA approval is based on results from the EMBER-3 trial. The study found that people with hormone receptor-positive breast cancer with an ESR1 mutation who took imlunestrant on its own lived about two months longer without the cancer growing (called progression-free survival) than people who received Faslodex (chemical name: fulvestrant) or took Aromasin (chemical name: exemestane).

See imlunestrant prescribing information.

Imlunestrant blocks the effects of estrogen on hormone receptor-positive breast cancer cells by sitting in the estrogen receptors on the cells. If imlunestrant is in the receptor, estrogen can’t attach to the cancer cell and the cell doesn’t receive estrogen’s signals to grow and multiply.

Imlunestrant also changes the shape of the estrogen receptors so they don’t work as well. 

Up to 40% of advanced-stage or metastatic, estrogen receptor-positive, HER2-negative breast cancers develop an ESR1 mutation while being treated with hormonal therapy. This mutation makes the cancer resistant to hormonal therapy medicines commonly used as first treatments: aromatase inhibitors and selective estrogen receptor modulators (SERMs).

But SERDs, like imlunestrant, Faslodex, and Orserdu (chemical name: elacestrant), can treat breast cancers with an ESR1 mutation. As the EMBER-3 and other studies have shown, newer SERDs like Orserdu and imlunestrant are more effective than Faslodex.

Imlunestrant is a pill taken by mouth. The recommended dose is 400 mg daily, taken as two 200 mg tablets once a day on an empty stomach (at least two hours before you eat anything or one hour after you eat).

Like almost all breast cancer medicines, imlunestrant can cause side effects, some of them serious.

The most common side effects of imlunestrant are:

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  anemia

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  bone pain

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  low calcium levels

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  low white blood cell counts

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  fatigue

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  diarrhea

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  nausea

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  constipation

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  abdominal pain

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  liver problems

Imlunestrant also may cause serious side effects, including hypercholesterolemia and hypertriglyceridemia. 

Hypercholesterolemia means your low-density lipoprotein (LDL), also called bad cholesterol, is too high. If this happens, fat can collect in your arteries, which increases your risk of heart attack and stroke.

Hypertriglyceridemia means you have too many triglycerides in your blood. Hypertriglyceridemia also increases your risk of heart attack and stroke. 

Before you start taking imlunestrant, your doctor should test the amount of cholesterol and triglycerides in your blood. These tests will be repeated as you continue to take the medicine.

Imlunestrant may cause harm to a fetus. You should not take imlunestrant if you are pregnant, trying to get pregnant, or if there is any chance that you could be pregnant. Women should use an effective non-hormonal type of birth control while taking imlunestrant. Ask your doctor which type of non-hormonal birth control would be best for you. Women should use birth control for at least one week after their last dose of imlunestrant. 

You shouldn’t breastfeed while taking imlunestrant and should wait at least one week after your last dose to start breastfeeding.

If you’re a man taking imlunestrant and have a partner who can become pregnant, your partner should use birth control while you’re taking imlunestrant and for at least one week after your last dose.

There are certain medicines and supplements you should avoid if you’re taking imlunestrant.

You should not take CYP3A4 inducers because they decrease the effects of imlunestrant. This class of medicine includes Rifamate (chemical name: rifampin), an antibiotic used to treat tuberculosis, and Carbatrol (chemical name: carbamazepine), which is used to control certain types of seizures in people with epilepsy. St. John’s wort, an herbal supplement, is also considered a CYP3A4 inducer.

You should not take CYP3A4 inhibitors because they increase the effects of imlunestrant. This class of medicine includes Nizoral (chemical name: ketoconazole) and Sporanox (chemical name: itraconazole), which are used to treat fungal infections; Reyataz (chemical name: atazanavir), used to treat HIV; and nefazodone, used to treat depression. Goldenseal, an herbal supplement, is also considered a CYP3A4 inhibitor.

It’s important to tell your doctor about all other medicines, vitamins, and supplements you take so they can determine whether imlunestrant is right for you.

The cost of imlunestrant may vary. The price you’ll pay depends on the drug manufacturer, your health insurance provider and plan, where you live, and the pharmacy you use. 

Note: Your insurance company may require you to get prior authorization before covering imlunestrant.

If your doctor prescribes imlunestrant and you have problems paying for it or getting health insurance coverage, Lilly, the company that makes imlunestrant, has access and affordability programs. You can also call 800-545-5979 for more information.

Learn more about financial assistance and medicine cost-lowering tips.