FDA Approves a Two-Drug Breast Cancer Treatment for Patients With One Gene Mutation

The Food and Drug Administration approved imlunestrant in combination with abemaciclib on Sept. 18, 2026, for adults with advanced or metastatic breast cancer whose tumors carry a mutation in the estrogen receptor gene, ESR1.

The approval covers hormone-driven disease, ER-positive and HER2-negative, that has kept growing after at least one course of hormone-blocking treatment, and only when an authorized test has found the mutation. The agency approved that test in the same decision: the Guardant360 CDx assay, which looks for ESR1 mutations in tumor DNA circulating in the blood. Patients whose tumors do not carry one of them are not covered.

Eli Lilly and Company makes both drugs, sold as Inluriyo and Verzenio, which are taken by mouth until the disease worsens or the side effects become intolerable. The approval rests on EMBER-3, a trial of 874 adults who had already been treated with an aromatase inhibitor, a standard hormone therapy. Participants were assigned to imlunestrant alone, imlunestrant with abemaciclib, or a hormone therapy their doctor chose.

In an exploratory analysis of 159 patients with ESR1-mutated tumors, which was not one of the trial's main comparisons, the FDA reports a median of 11.1 months before the disease worsened on the combination, against 5.5 months on imlunestrant alone. The agency says the benefit appeared only in patients with the mutation: imlunestrant on its own did not beat the therapy chosen by a patient's doctor, in the full trial population or among patients without the mutation. Whether the combination helps people live longer is not yet known; the survival data were still immature at the interim analysis.

Abemaciclib's label carries warnings for diarrhea, low white-blood-cell counts, lung inflammation, liver injury and blood clots, and both labels warn of harm to a fetus. The FDA has also approved another drug for advanced breast cancer with this mutation, AstraZeneca's camizestrant.