On August 18, 2025 Merck & Co. reported that Ifinatamab deruxtecan (I-DXd) has been granted Breakthrough Therapy Designation (BTD) by the U.S. Food and Drug Administration (FDA) for the treatment of adult patients with extensive-stage small cell lung cancer with disease progression on or after platinum-based chemotherapy (Press release, Merck & Co, AUG 18, 2025, View Source [SID1234655360]).
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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 (TSE: 4568) and being jointly developed by Daiichi Sankyo and Merck (NYSE: MRK), known as MSD outside of the United States and Canada.
The FDA BTD is designed to accelerate the development and regulatory review of potential new medicines that are intended to treat a serious condition and address a significant unmet medical need. The medicine is required to have shown encouraging preliminary clinical results that demonstrate substantial improvement on a clinically significant endpoint over currently available medicines.
The FDA granted the BTD based on data 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 will be presented in a late-breaking oral presentation at the IASLC 2025 World Conference on Lung Cancer hosted by the International Association for the Study of Lung Cancer (#WCLC25). This is the first BTD for ifinatamab deruxtecan and represents the first BTD since the start of the Daiichi Sankyo and Merck collaboration.
"This Breakthrough Therapy Designation granted by the FDA to ifinatamab deruxtecan highlights the urgent need for new treatment options for patients with pretreated extensive-stage small cell lung cancer," said Ken Takeshita, MD, global head, R&D, Daiichi Sankyo. "We are committed to advancing this medicine with the goal of bringing the first B7-H3 directed antibody drug conjugate to patients in order to transform the outcomes of those facing this aggressive disease."
"Patients living with extensive-stage small cell lung cancer often have limited therapeutic options following disease progression after standard of care treatments," said Eliav Barr, MD, senior vice president, head of global clinical development and chief medical officer, Merck Research Laboratories. "This Breakthrough Therapy Designation reinforces our confidence in the promise of ifinatamab deruxtecan to play an important role in the treatment of extensive-stage small cell lung cancer, and we are looking forward to sharing data at the upcoming IASLC 2025 World Conference on Lung Cancer that show the potential of this novel option."
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 extensive-stage small cell lung cancer 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.
In the first part of the trial (dose optimization), patients were randomized 1:1 to receive ifinatamab deruxtecan 8 or 12 mg/kg intravenously Q3W. In the second part of the trial (dose expansion), patients received ifinatamab deruxtecan 12 mg/kg intravenously Q3W.
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, progression-free survival, disease control rate, time to response, overall survival, 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-resistance 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 overall response rate, duration of response, disease control rate, progression-free survival, overall survival and safety. Pharmacokinetic endpoints, exploratory biomarker and immunogenicity endpoints will also be assessed.
IDeate-PanTumor01 enrolled approximately 250 patients in Asia and North America. For more information about the trial, visit ClinicalTrials.gov.
About small cell lung cancer
More than 2.48 million lung cancer cases were diagnosed globally in 2022. Small cell lung cancer (SCLC) is the second most common type of lung cancer, accounting for approximately 15% of 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 any cancer.
About ifinatamab deruxtecan
Ifinatamab deruxtecan (I-DXd) 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 has been granted orphan drug designation 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.
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 anticancer medicines across multiple cancers.