FDA Approves Lilly's Inluriyo-Verzenio Combo for ESR1-Mutated Breast Cancer

The Food and Drug Administration on September 18 approved imlunestrant (Inluriyo) in combination with abemaciclib (Verzenio) for 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. Both drugs are manufactured by Eli Lilly and Company. The approval rests on the phase 3 EMBER-3 trial, where the combination doubled median progression-free survival — 11.1 months versus 5.5 months with imlunestrant alone — in the 159 patients with ESR1-mutated tumors, cutting the risk of progression or death by nearly half. The agency also approved the Guardant360 CDx assay as a companion diagnostic, making an FDA-authorized ESR1 test a formal part of selecting patients for the all-oral regimen. Overall survival data were not yet mature.

What the approval covers

The indication is narrow by design. It applies only to adults with ER-positive, HER2-negative advanced or metastatic breast cancer carrying an ESR1 mutation detected by an FDA-authorized test, with disease progression following at least one line of endocrine therapy. Tumor testing is now a formal gate: the mutation must be identified with an authorized test before the regimen can be used.

Both drugs come from the same maker. Imlunestrant (Inluriyo) and abemaciclib (Verzenio) are manufactured by Eli Lilly and Company, making this an all-Lilly pairing. Alongside the drugs, the FDA approved the Guardant360 CDx assay as the companion diagnostic to identify patients whose tumors carry the ESR1 mutation.

The EMBER-3 evidence

Efficacy was evaluated in EMBER-3, a randomized, open-label, active-controlled, multicenter trial that enrolled 874 adults with ER-positive, HER2-negative locally advanced or metastatic breast cancer previously treated with an aromatase inhibitor, alone or in combination with a CDK4/6 inhibitor. Patients were randomized one-to-one-to-one to imlunestrant, an investigator's choice of endocrine therapy (fulvestrant or exemestane), or imlunestrant plus abemaciclib. Patients eligible to receive a PARP inhibitor were excluded.

The approval hinges on an exploratory subgroup: 159 patients with ESR1-mutated tumors, 67 on the combination and 92 on imlunestrant alone. In that group, median progression-free survival was 11.1 months (95% CI, 7.4–13.7) with the combination versus 5.5 months (95% CI, 3.8–7.2) with imlunestrant alone — a hazard ratio of 0.53 (95% CI, 0.35–0.80). The objective response rate was 35% versus 15%.

Two caveats matter. The subgroup analysis was exploratory, and overall survival data were immature at the interim analysis, with a 35% death rate in the ESR1-mutated population. The FDA also notes that imlunestrant monotherapy did not show a statistically significant improvement over investigator's-choice endocrine therapy in the overall or ESR1-not-detected populations — the benefit was confined to the ESR1-mutated group.

Safety and dosing

The recommended dosage is imlunestrant 400 mg taken orally once daily on an empty stomach, with abemaciclib 150 mg taken orally twice daily.

The safety profile blends the two drugs' labeled risks. Imlunestrant carries a warning for embryo-fetal toxicity. Abemaciclib's warnings include diarrhea, neutropenia, interstitial lung disease or pneumonitis, hepatotoxicity, venous thromboembolism, and embryo-fetal toxicity.

What it means for Lilly

The approval extends the labeled use of two Lilly-owned cancer drugs in a single regimen — and it is the second FDA action this month in ESR1-mutated breast cancer. On September 4 the agency granted accelerated approval to AstraZeneca's Etcamah (camizestrant) for the same biomarker-defined population in the SERENA-6 trial, a story TickerGrove covered on September 6. The two approvals target the same resistance mutation with a different endocrine therapy and different trial evidence; they are not the same approval.

For physicians, the practical result is a new option at the point where hormone-blocking therapy has stopped working and a blood test shows the tumor has acquired an ESR1 resistance mutation. For Lilly, the combination keeps both drugs inside its own portfolio rather than pairing with a competitor's agent.

What to watch: full prescribing information for both drugs will be posted on Drugs@FDA, and uptake will depend on how widely oncologists order the companion ESR1 test. The immature survival data also leaves an open question for longer-term follow-up.