On April 13, 2026 Daiichi Sankyo (TSE: 4568) and Merck’s (NYSE: MRK), known as MSD outside of the United States and Canada, reported that Biologics License Application (BLA) for ifinatamab deruxtecan (I-DXd) has been accepted and granted Priority Review by the U.S. Food and Drug Administration (FDA) for the treatment of adult patients with extensive-stage small cell lung cancer (ES-SCLC) with disease progression on or after platinum-based chemotherapy. The Prescription Drug User Fee Act (PDUFA) date, the FDA action date for its regulatory decision, is October 10, 2026.
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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.
The FDA grants Priority Review to applications for medicines that, if approved, would offer significant improvements over available treatment options by demonstrating safety or efficacy improvements, preventing serious conditions or enhancing patient compliance. The FDA is also reviewing the BLA under the Real-Time Oncology Review (RTOR) program and Project Orbis, two initiatives of the FDA which are designed to bring safe and effective cancer treatments to patients as early as possible. RTOR allows the FDA to review components of an application before submission of the complete application. Project Orbis provides a framework for concurrent submission and review of oncology medicines among participating international partners.
The BLA is based on results from the IDeate-Lung01 Phase 2 trial, with support from the IDeate-PanTumor01 Phase 1/2 trial. Results from the primary analysis of IDeate-Lung01 were presented at the 2025 World Conference on Lung Cancer hosted by the International Association for the Study of Lung Cancer (#WCLC25) and published in the Journal of Clinical Oncology. Ifinatamab deruxtecan also was previously granted Breakthrough Therapy Designation by the FDA in August 2025 for the treatment of adult patients with ES-SCLC with disease progression on or after platinum-based chemotherapy.
"The FDA’s granting of Priority Review for ifinatamab deruxtecan marks a significant milestone in our effort to provide new and innovative treatment options for patients with extensive-stage small cell lung cancer," said John Tsai, MD, global head, R&D, Daiichi Sankyo. "We look forward to continuing to work with the FDA to bring this potential first-in-class B7-H3 directed DXd antibody drug conjugate to patients as quickly as possible."
"Small cell lung cancer remains one of the toughest cancers to treat, with few options if the disease progresses after standard of care treatments," said Eliav Barr, MD, senior vice president, head of global clinical development and chief medical officer, Merck Research Laboratories. "The FDA’s acceptance of the BLA reinforces the important role that ifinatamab deruxtecan could play in helping to address the needs of patients with extensive-stage small cell lung cancer."
About IDeate-Lung01
IDeate-Lung01 is a global, multicenter, randomized, open-label, two-part Phase 2 trial evaluating the safety and efficacy of ifinatamab deruxtecan in patients with ES-SCLC who were previously treated with at least one prior line of platinum-based chemotherapy and a maximum of three prior lines of therapy. Patients with asymptomatic brain metastases (untreated or previously treated) were eligible to participate.
In the first part of the trial (dose optimization), patients were randomized 1:1 to receive ifinatamab deruxtecan (8 or 12 mg/kg) given intravenously once every three weeks. In the second part of the trial (dose expansion), patients received ifinatamab deruxtecan (12 mg/kg) intravenously at the same dosing interval.
The primary endpoint is objective response rate (ORR) as assessed by blinded independent central review (BICR) per RECIST v1.1. Secondary endpoints included duration of response (DOR), progression-free survival (PFS), disease control rate (DCR), time to response (TTR), overall survival (OS), pharmacokinetics and safety. Intracranial ORR was assessed by BICR as an exploratory analysis.
IDeate-Lung01 enrolled 187 patients in Asia, Europe and North America. For more information about the trial, visit ClinicalTrials.gov.
About IDeate-PanTumor01
IDeate-PanTumor01 is a global, multicenter, first-in-human, open-label Phase 1/2 trial evaluating the safety and efficacy of ifinatamab deruxtecan in patients with advanced/unresectable or metastatic solid tumors that are refractory or intolerable to standard treatment or for whom no standard treatment exists.
The Phase 1 part of the trial (dose escalation) is assessing the safety and tolerability of increasing doses of ifinatamab deruxtecan to determine the maximum tolerated dose and recommended dose for expansion (RDE). The Phase 2 part of the trial (dose expansion) is evaluating the safety and efficacy of ifinatamab deruxtecan at the RDE of 12 mg/kg in patients with squamous non-small cell lung cancer, metastatic castration-resistant prostate cancer or esophageal squamous cell carcinoma.
The dose escalation part of the trial is evaluating dose-limiting toxicity and safety. The dose expansion part of the trial is evaluating ORR, DOR, DCR, PFS, OS and safety. Pharmacokinetic endpoints, exploratory biomarker and immunogenicity endpoints also will be assessed.
IDeate-PanTumor01 will enroll approximately 250 patients in Asia and North America. For more information about the trial, visit ClinicalTrials.gov.
About small cell lung cancer
Approximately 250,000 patients are diagnosed with small cell lung cancer (SCLC) each year globally. There were approximately 27,000 new cases of SCLC in the U.S. in 2025, accounting for about 12% of all lung cancer cases. SCLC is aggressive and progresses rapidly to the distant metastatic stage, which has a low five-year survival rate. While conventional standard of care treatments for patients with advanced SCLC may help improve outcomes, there is a need for additional subsequent treatment approaches.
About B7-H3
B7-H3 is a transmembrane protein that belongs to the B7 family of proteins, which bind to the CD28 family of receptors that includes PD-1. B7-H3 is overexpressed in a wide range of cancer types, including SCLC, and its overexpression has been shown to correlate with poor prognosis, making B7-H3 a promising therapeutic target. There are currently no B7-H3 directed medicines approved for the treatment of cancer.
About ifinatamab deruxtecan
Ifinatamab deruxtecan is an investigational potential first-in-class B7-H3 directed ADC. Designed using Daiichi Sankyo’s proprietary DXd ADC Technology, ifinatamab deruxtecan is comprised of a humanized anti-B7-H3 IgG1 monoclonal antibody attached to a number of topoisomerase I inhibitor payloads (an exatecan derivative, DXd) via tetrapeptide-based cleavable linkers.
Ifinatamab deruxtecan was granted Breakthrough Therapy Designation by the FDA for the treatment of adult patients with ES-SCLC with disease progression on or after platinum-based chemotherapy.
Ifinatamab deruxtecan has been granted Orphan Drug Designation (ODD) by the U.S. FDA, European Commission, Japan Ministry of Health, Labour and Welfare and Taiwan Food and Drug Administration for the treatment of SCLC. Ifinatamab deruxtecan also was granted ODD for the treatment of esophageal cancer by the FDA.
About the ifinatamab deruxtecan clinical development program
A comprehensive global clinical development program is underway evaluating the efficacy and safety of ifinatamab deruxtecan monotherapy and in combination with other cancer medicines across multiple cancers. The program is currently comprised of three Phase 3 trials in advanced/metastatic disease, including SCLC (IDeate-Lung02), castration-resistant prostate cancer (IDeate-Prostate01) and esophageal squamous cell carcinoma (IDeate-Esophageal01).
(Press release, Merck & Co, APR 13, 2026, View Source [SID1234664330])