You probably know how it goes when a loved one gets a cancer diagnosis.
The first weeks are full of appointments, acronyms, and hard questions about what comes next.
For one of the toughest lung cancers, the list of answers has been very short.
On September 25, 2026, Daiichi Sankyo and Merck pulled their US application for ifinatamab deruxtecan, a treatment for a form of small cell lung cancer that keeps growing after platinum chemotherapy.
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According to Cancer Network, the decision came 15 days before the FDA was due to answer.
The companies said the FDA had concluded that the data they had were not strong enough to support an accelerated approval. That outcome followed talks with the agency about results from a mid-stage trial called IDeate-Lung01.
Ifinatamab deruxtecan, often shortened to I-DXd, is an antibody-drug conjugate. The antibody latches onto a protein called B7-H3, which sits on many small cell lung cancer tumors, and carries a cell-killing drug directly to those cells.
Extensive-stage small cell lung cancer has already spread beyond the lung by the time it is found. Median survival at this stage is often less than a year, and once first-line chemotherapy stops working, few proven options are left.
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What the trial actually showed
The IDeate-Lung01 phase 2 trial tested I-DXd in 137 adults whose cancer had come back after platinum-based chemotherapy.
Tumors shrank in about 48 percent of patients, and median overall survival was 10.3 months, according to OncoDaily.
Those numbers looked promising for a disease with so few second-line options. But the FDA weighs response rates less heavily when a drug has not been compared directly against another treatment in a larger trial.
Safety data also drew attention. About one in three patients had serious treatment-related side effects. Inflammation of the lungs, known as interstitial lung disease, affected roughly 12 percent of patients, and two of those cases were fatal.
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What this means for patients now
For now, ifinatamab deruxtecan is not available in the United States for small cell lung cancer. The withdrawal removes the near-term path to approval in this setting, but it does not end development of the drug.
A larger phase 3 trial called IDeate-Lung02 is still running. It compares I-DXd directly against chemotherapy chosen by the treating doctor in people whose extensive-stage cancer has come back after a first round of platinum treatment.
Daiichi Sankyo has said enrollment in that trial is near completion, and the companies plan to decide on a future FDA filing based on those results.
People in treatment with questions about options can ask their oncologist whether IDeate-Lung02 or another clinical trial is open to them.
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This article is made and published by Ida-Marie Palm Varbæk, who may have used AI in the preparation.