Inluriyo for Breast Cancer

Written by Christie Denton, BCPS, PharmD
Medically Reviewed by Rachel Maynard, PharmD on November 02, 2025
6 min read

Breast cancer is one of the most common types of cancer in women in the United States. Each year, approximately 30% of newly diagnosed cancers in women are breast cancer. There are many treatments available for breast cancer. The type of treatment depends on the type of breast cancer you have.

Breast cancer that grows and spreads in the presence of the hormone estrogen is known as estrogen-receptor (ER)-positive cancer. In about 20% of breast cancers, cancer cells may also have a lot of growth of a protein known as human epidermal growth factor receptor 2 (HER2). HER2-positive breast cancers tend to spread more quickly than HER2-negative breast cancers. Some people with ER-positive cancer can also have a specific gene mutation known as the estrogen receptor-1 (ESR1) mutation. This mutation can make certain treatments, such as some types of hormone therapy, not work as well.

In ER-positive breast cancer, hormone therapy is often used after surgery to lower the chance of cancer coming back. Sometimes, hormone therapy is started before surgery. There are several types of hormone therapy available to treat breast cancer. One type is selective estrogen receptor degraders (SERDs). SERDs are most often used in people who have gone through menopause. If used before menopause, SERDs are given along with another medicine that shuts down the ovaries.

When treating ER-positive breast cancer, hormone therapy can sometimes be given with targeted drug therapies that block certain cyclin-dependent kinases (CDK), known as CDK 4/6 inhibitors. Examples of CDK 4/6 inhibitors include abemaciclib, palbociclib, and ribociclib.

Inluriyo (imlunestrant) is used to treat people with ER-positive, HER2-negative breast cancer with an ESR1 mutation, whose cancer is advanced or metastatic (spreads to other body sites) and has progressed (gotten worse) despite treatment with at least one prior hormone therapy. Inluriyo is a SERD.

A clinical trial looked at whether Inluriyo was safe and effective for treating advanced or metastatic breast cancer. Inluriyo alone was compared to either Inluriyo plus abemaciclib or to standard hormone therapy alone (exemestane or fulvestrant). People in the study knew what medicine they were taking.

The trial included 874 adults diagnosed with ER-positive, HER2-negative advanced or metastatic breast cancer that had recurred (come back) or progressed during or after treatment with an aromatase inhibitor (a type of hormone therapy), with or without a CDK 4/6 inhibitor. People were not allowed in the study if they could take a poly (ADP-ribose) polymerase (PARP) inhibitor (such as olaparib or talazoparib).

People in the study received one of the following regimens.

●        Inluriyo 400 milligrams (mg) by mouth once daily,

●        Exemestane 25 mg by mouth once daily or fulvestrant 500 mg injection into a muscle every two weeks initially for three doses, then once monthly

●        Inluriyo 400 mg by mouth once daily plus abemaciclib 150 mg by mouth twice daily

People were assigned treatment based on where they lived, their prior treatment, and if they had metastases (cancer spreading to certain internal organs). People continued on treatment until their cancer got worse or they had a side effect that was not manageable.

Of the people in the study with an ESR1 mutation, the median (middle) age was 61 years (range, 28-85 years). All of these people were female, and about 11% of them were pre- or perimenopausal. Sixty-one percent were White, 26% were Asian, 4% were Black, 4% were American Indian or Alaskan Native, 4.7% had an unknown race, 0.8% were of multiple races, and 19% were Hispanic or Latino. Most (59%) had cancer that had spread to internal organs before receiving treatment. Overall, 79% of people had received a certain type of prior hormone therapy, and 21% had not. Most people (70%) had taken a CDK 4/6 inhibitor before the study, and 67% of these people had advanced or metastatic breast cancer.

Every eight weeks, people had an MRI or CT scan to assess the status of their cancer. After a year, scans were done every 12 weeks until cancer had progressed.

Out of the 256 people with an ESR1 mutation, those taking Inluriyo had their cancer progress after a median of 5.5 months, compared to a median of 3.8 months in people who took the hormone therapy fulvestrant or exemestane.

There was a greater number of people taking Inluriyo (13.4%) who also had their cancer partially respond (cancer was reduced) compared to 7.7% who were taking fulvestrant or exemestane. A small number of people (0.9%) taking Inluriyo had cancer that completely responded to treatment (cancer was not detectable) compared to none taking fulvestrant or exemestane.

Your results may differ from what was seen in clinical studies.

Side effects are common with medicines that treat cancer, including Inluriyo. It is important to tell your health care provider about any side effects you have during and after taking Inluriyo. The most common side effects with Inluriyo include abnormal blood test results (including increased cholesterol and triglycerides), muscle or bone pain, tiredness, nausea, constipation, stomach pain, and diarrhea.

Your health care provider will have you do blood tests regularly while taking Inluriyo. It is important that you do not miss any of your appointments so your health care provider can make sure the medicine is safe for you. If your health care provider notices that your blood test results are abnormal or you are having side effects, your Inluriyo regimen may need to be adjusted.

If you have muscle or bone pain, you should tell your health care provider about your symptoms, as they may want to check your blood. You should also talk to your health care provider before taking any over-the-counter (OTC) medicine to treat your symptoms.

To help limit nausea and vomiting, you can try simple methods, such as eating bland foods like toast or crackers. Your health care provider may also prescribe medicine to help manage nausea and vomiting.

To manage constipation, you can try drinking plenty of fluids, exercising, and eating plenty of fiber. These methods can also help manage any stomach pain you may have. If changing your diet and habits does not work, you can try an OTC laxative, although these should be used sparingly. Talk to your health care provider before taking an OTC medicine to treat your constipation.

Since your cholesterol and triglycerides can increase while taking Inluriyo, your health care provider will regularly check your lipid levels throughout treatment.

If your side effects get worse or do not improve, talk with your health care provider.

Some medicines can interact with Inluriyo. If your dose of Inluriyo is not adjusted to account for the interacting medicine, you can have a higher risk of side effects from Inluriyo, or it may not work as well.

Strong inhibitors or inducers of cytochrome P450 3A (CYP3A). Cytochrome P450 3A is an enzyme that processes and removes some medicines from the body. Taking certain medicines that strongly inhibit (decrease the activity of) or induce (increase the activity of) this enzyme can increase the risk of side effects from Inluriyo or cause it to not work as well.

Ask your pharmacist or other health care provider if any of your medicines are a strong CYP3A inhibitor or inducer. You may need to avoid certain medicines while taking Inluriyo, or your dose of Inluriyo may need to be adjusted.

Other types of medicines may also interact with Inluriyo. Tell your pharmacist or other health care provider about all prescription or OTC medicines, vitamins/herbals, herbal products, or other supplements you have recently taken. This will help them know if there are any interactions with Inluriyo.

Because Inluriyo is not safe to take during pregnancy or while breastfeeding, your health care provider will test to make sure you are not pregnant before starting the medicine. It is recommended that you avoid breastfeeding while taking Inluriyo and for one week after the last dose.

If you can become pregnant or have a partner who can become pregnant, you should use effective contraception (birth control) while taking Inluriyo and for one week after the last dose.

There is a cost support program from the drugmaker that may allow you to pay as little as $0 per month. Whether you are eligible depends on whether you have prescription insurance and what type of insurance you have. You can find out more inluriyo.lilly.com/savings-support or by calling 800-545-5979.