Ifinatamab Deruxtecan Biologics License Application for Certain Patients with Previously Treated Extensive-Stage Small Cell Lung Cancer Voluntarily Withdrawn

TOKYO, September 25, 2026--The Biologics License Application (BLA) seeking accelerated approval in the U.S. for Daiichi Sankyo (TSE: 4568) and Merck's (NYSE: MRK), known as MSD outside of the United States and Canada, ifinatamab deruxtecan (I-DXd) for the treatment of adult patients with extensive-stage small cell lung cancer (ES-SCLC) with disease progression on or after platinum-based chemotherapy has been voluntarily withdrawn.

The decision to withdraw the BLA is based on discussions with the U.S. Food and Drug Administration (FDA) that data supporting the application, including from the IDeate-Lung01 phase 2 trial, do not satisfy requirements needed to support an accelerated approval for the proposed indication. The accelerated approval pathway in the U.S. allows for earlier approval of medicines based on surrogate endpoints to treat serious conditions where there is an unmet medical need.

Patient enrollment continues in the IDeate-Lung02 phase 3 trial evaluating the efficacy and safety of ifinatamab deruxtecan versus treatment of physician's choice of chemotherapy (amrubicin, lurbinectedin or topotecan) in patients with relapsed ES-SCLC following disease progression with only one prior line of platinum-based chemotherapy.

Ifinatamab deruxtecan is a specifically engineered, potential first-in-class B7-H3 directed DXd antibody drug conjugate (ADC) discovered by Daiichi Sankyo and being jointly developed by Daiichi Sankyo and Merck.

"Extensive-stage small cell lung cancer is a challenging disease to treat, leaving patients in need of new options," said Abderrahmane Laadem, MD, Head, Therapeutic Area Oncology Development, Daiichi Sankyo. "Enrollment into the IDeate-Lung02 phase 3 trial is near completion and we look forward to assessing the potential for a future filing of ifinatamab deruxtecan with the FDA and other global regulatory authorities based on those results."

"While we are disappointed that the current dataset are not supportive of an approval at this time, we are continuing to evaluate the role of ifinatamab deruxtecan in patients with extensive-stage small cell lung cancer and other types of difficult-to-treat cancer," said Marjorie Green, MD, Senior Vice President, Head of Oncology Global Clinical Development, Merck Research Laboratories. "We would like to thank the patients, their families and investigators who have participated or continue to participate in these studies."

In addition to the IDeate-Lung02 phase 3 trial, there are two additional phase 3 trials underway with ifinatamab deruxtecan in advanced/metastatic disease, including IDeate-Prostate01 for castration-resistant prostate cancer (CRPC) and IDeate-Esophageal01 for esophageal squamous cell carcinoma (ESCC).