Median progression-free survival of 11.1 months with the combination, against 5.5 months for imlunestrant alone. That is the figure behind the FDA’s September 18 full approval of Eli Lilly’s Inluriyo (imlunestrant) with Verzenio (abemaciclib) for a narrow group of breast cancer patients.
The approval covers adults with estrogen receptor-positive, HER2-negative, ESR1-mutated advanced or metastatic breast cancer whose disease progressed after at least one line of endocrine therapy. The mutation must be confirmed by an FDA-authorized test, and the agency also cleared the Guardant360 CDx blood assay as the companion diagnostic. This is not a first treatment. It applies once hormone-blocking therapy has stopped working. In about half of people with this type of metastatic breast cancer, tumors pick up an ESR1 mutation during or after treatment with an aromatase inhibitor.
What EMBER-3 showed
The randomized, open-label EMBER-3 trial enrolled 874 adults previously treated with an aromatase inhibitor, with or without a CDK4/6 inhibitor. They received imlunestrant alone, an investigator’s choice of endocrine therapy, or imlunestrant plus abemaciclib. The headline result comes from an exploratory subgroup of 159 patients with ESR1 mutations: a hazard ratio of 0.53, and an objective response rate of 35% versus 15%.
Two limits matter. Overall survival data were immature at interim analysis, with deaths in 35% of the ESR1-mutated group, so the trial has not shown that people live longer. And imlunestrant alone did not beat standard endocrine therapy in the overall population or in patients without the mutation, so the benefit appears confined to those with it.
Dr. Komal Jhaveri of Memorial Sloan Kettering, principal investigator for EMBER-3, called combining drugs that act on the estrogen receptor and CDK4/6 “an important strategy to help address treatment resistance.” Memorial Sloan Kettering discloses that she has financial interests tied to Lilly, which sponsored the trial.
Side effects and testing
The regimen has a cost. Diarrhea hit 86% of patients on the combination, with grade 3 or 4 cases in 9%. Neutrophil counts fell in 86%, severely in 21%. Interstitial lung disease or pneumonitis occurred in 2.9% and venous thromboembolic events in 4.8%. Serious adverse reactions affected 21%, and fatal ones 3.8%. Permanent discontinuation was low: 1% for imlunestrant, 3.4% for abemaciclib.
Blood counts and liver function are checked before starting, every two weeks for two months, then monthly for two months. Imlunestrant is taken once daily on an empty stomach, abemaciclib twice daily. Patients should report loose stools at the first sign.
In the trial, ESR1 status came from circulating tumor DNA in a blood sample, not a tissue biopsy, and a liquid biopsy is easier to repeat. Patients whose cancer is progressing can ask their oncologist whether ESR1 testing has been done, and when. Both drugs are oral and usually fall under a pharmacy benefit, where cost-sharing can be steep, so coverage is worth raising with the care team early.
Imlunestrant was first cleared as a single agent in September 2025. Results from EMBER-4, which tests it after surgery in more than 8,000 patients with early breast cancer, are expected in 2027. The encouraging part is a new option for a hard-to-treat stage; whether it suits any one patient is a question to take to your doctor.
