The US Food and Drug Administration granted full approval on 18 September 2026 to imlunestrant (Inluriyo) in combination with abemaciclib (Verzenio) for adults with oestrogen receptor-positive, HER2-negative, ESR1-mutated locally advanced or metastatic breast cancer whose disease has progressed after at least one line of endocrine therapy, according to a report by OncoDaily reviewed by three oncologists. The ESR1 mutation must be identified with a test authorised by the FDA. The decision rests on the phase III EMBER-3 trial and is the second US approval for imlunestrant in under a year, after its approval as monotherapy in September 2025.
The approval applies in the United States. It says nothing about availability in the UK or the European Union, where the MHRA and the European Medicines Agency make their own assessments.
What the evidence shows in numbers
The combination approval is supported by 159 patients with ESR1-mutated disease in EMBER-3. Of those, 92 received imlunestrant alone and 67 received imlunestrant plus abemaciclib. Median progression-free survival was 11.1 months with the combination against 5.5 months with imlunestrant alone, a hazard ratio of 0.53 with a 95% confidence interval of 0.35 to 0.80. In absolute terms, the median time before the disease progressed or the patient died was about 5.6 months longer with the combination.
Three limits belong next to those figures. The endpoint is progression-free survival, not overall survival, and the report gives no overall survival data for this comparison. The analysis covers 159 patients, a modest number for a phase III decision. And the comparator is imlunestrant alone, not the full range of treatments a patient in this position might otherwise receive.
Why the ESR1 mutation defines the population
ESR1 mutations are one of the best-described ways ER-positive metastatic breast cancer becomes resistant to aromatase inhibitors, allowing the oestrogen receptor to stay active even when oestrogen production is suppressed. The approval announcement, as reported, says such mutations may develop in around half of patients with ER-positive, HER2-negative metastatic disease during or after aromatase inhibitor treatment. Imlunestrant is an oral oestrogen receptor antagonist and degrader. Abemaciclib inhibits CDK4 and CDK6, the proteins that drive cell division in hormone receptor-positive disease, so the combination acts on two pathways at once.
Full approval rather than accelerated
The FDA granted full approval rather than accelerated approval, so the decision does not depend on a later confirmatory trial. EMBER-3 enrolled patients whose disease had progressed on aromatase inhibitor-based treatment, with or without a previous CDK4/6 inhibitor, and in many cases the strategy involved switching both the endocrine therapy and the CDK4/6 inhibitor. The report notes that the adverse event profile of the combination reflects the addition of abemaciclib, and clinicians will weigh that against the benefit for each patient.
What remains unknown
Overall survival for the ESR1-mutated combination group is the main missing figure, and it will decide how the combination is placed against other options in the increasingly biomarker-driven sequence after CDK4/6 treatment. The second open question is regulatory, because no UK or EU decision on the combination has been reported. Patients with questions about their own treatment should speak to their oncology team. The OncoDaily report is here.
