Iftinitamab Deruxtecan Shows Clinically Meaningful Response in Extensive-Stage SCLC Patients: IDeate-Lung01 Phase 2 Trial Results

09/07/2025 – 10:45 AM

• An objective response rate of 48.2% was observed with ifinatamab deruxtecan in these previously treated patients
• Discussions with global regulatory authorities underway

BASKING RIDGE, N.J. & RAHWAY, N.J.–In a potential breakthrough for patients battling extensive-stage small cell lung cancer (ES-SCLC), Daiichi Sankyo (TSE: 4568) and Merck (NYSE: MRK) announced promising results from the IDeate-Lung01 phase 2 trial. The data, presented at the 2025 World Conference on Lung Cancer, showcase the efficacy of ifinatamab deruxtecan (I-DXd), a novel antibody-drug conjugate (ADC), in previously treated patients. The investigational drug is being jointly developed by Daiichi Sankyo and Merck, known as MSD outside of the United States and Canada.

ES-SCLC, characterized by its aggressive nature and rapid progression, poses a significant challenge to oncologists. The disease often carries a dismal prognosis, with a low five-year survival rate, underscoring the urgent need for innovative therapeutic strategies beyond the current standard of care.

The IDeate-Lung01 trial involved patients who had progressed after prior platinum-based chemotherapy. The headline from the study is the 48.2% confirmed objective response rate (ORR) observed in these patients, as assessed by blinded independent central review (BICR). The data revealed 3 complete responses (CRs) and 63 partial responses (PRs). Furthermore, the median duration of response (DOR) was 5.3 months, with a disease control rate (DCR) of 87.6%. Progression-free survival (PFS) reached 4.9 months and overall survival (OS) reached 10.3 months.

A notable finding emerged from a subset analysis of patients (n=32) who received ifinatamab deruxtecan as a second-line treatment, where a confirmed ORR soared to 56.3%. This group also saw a median DOR of 7.2 months and a DCR of 96.9%. Median PFS was 5.6 months and median OS reached 12.0 months.

An exploratory analysis focusing on patients with brain metastases at baseline (n=65) revealed an intracranial ORR of 46.2%, suggesting potential for I-DXd to address this particularly challenging aspect of SCLC. A more detailed subgroup analysis is scheduled for presentation at the upcoming 2025 European Society for Medical Oncology (ESMO) congress.

According to Dr. Myung-Ju Ahn, Professor at Samsung Medical Center, the results of IDeate-Lung01 provide further evidence of the potential role that ifinatamab deruxtecan could play in treating this aggressive form of lung cancer.

Ken Takeshita, MD, Global Head of R&D at Daiichi Sankyo, highlighted that the data would support ongoing discussions with global regulatory authorities, with Ken Takeshita reinforcing the potential benefit of this B7-H3 directed antibody drug conjugate.

The safety profile exhibited in IDeate-Lung01 aligned with previous observations of ifinatamab deruxtecan, introducing no new safety concerns. However, it’s worth noting that Grade 3 or higher treatment-related adverse events (TRAEs) were present in 36.5% of patients. Seventeen patients (12.4%) were reported with treatment-related interstitial lung disease (ILD)/pneumonitis.

Dr. Eliav Barr, Senior Vice President and Chief Medical Officer at Merck Research Laboratories, stated that there is a high unmet need for new medicines and novel mechanisms of action that could provide additional options to 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 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 ORR as assessed by BICR per RECIST v1.1. Secondary endpoints included DOR, PFS, DCR, TTR, 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.

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 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 U.S. Food and Drug Administration (FDA) for the treatment of adult patients with extensive-stage SCLC with disease progression on or after platinum-based chemotherapy.

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 cancer medicines across multiple cancers.

About the Daiichi Sankyo and Merck Collaboration
Daiichi Sankyo and Merck, known as MSD outside of the United States and Canada, entered into a global collaboration in October 2023 to jointly develop and commercialize patritumab deruxtecan (HER3-DXd), ifinatamab deruxtecan (I-DXd) and raludotatug deruxtecan (R-DXd), except in Japan where Daiichi Sankyo will maintain exclusive rights. Daiichi Sankyo will be solely responsible for manufacturing and supply. In August 2024, the global co-development and co-commercialization agreement was expanded to include gocatamig (MK-6070/DS3280), which the companies will jointly develop and commercialize worldwide, except in Japan where Merck & Co., Inc., Rahway, N.J., USA will maintain exclusive rights. Merck & Co., Inc., Rahway, N.J., USA will be solely responsible for manufacturing and supply for gocatamig.

About the ADC Portfolio of Daiichi Sankyo
The Daiichi Sankyo ADC portfolio consists of seven ADCs in clinical development crafted from two distinct ADC technology platforms discovered in-house by Daiichi Sankyo.

The ADC platform furthest in clinical development is Daiichi Sankyo’s DXd ADC Technology where each ADC consists of a monoclonal antibody attached to a number of topoisomerase I inhibitor payloads (an exatecan derivative, DXd) via tetrapeptide-based cleavable linkers. The DXd ADC portfolio currently consists of ENHERTU^®, a HER2 directed ADC, and DATROWAY^®, a TROP2 directed ADC, which are being jointly developed and commercialized globally with AstraZeneca. Patritumab deruxtecan (HER3-DXd), a HER3 directed ADC, ifinatamab deruxtecan (I-DXd), a B7-H3 directed ADC, and raludotatug deruxtecan (R-DXd), a CDH6 directed ADC, are being jointly developed and commercialized globally with Merck & Co., Inc., Rahway, N.J., USA. DS-3939, a TA-MUC1 directed ADC, is being developed by Daiichi Sankyo.

The second Daiichi Sankyo ADC platform consists of a monoclonal antibody attached to a modified pyrrolobenzodiazepine (PBD) payload. DS-9606, a CLDN6 directed PBD ADC, is the first of several planned ADCs in clinical development utilizing this platform.

Ifinatamab deruxtecan, patritumab deruxtecan, raludotatug deruxtecan, DS-3939 and DS-9606 are investigational medicines that have not been approved for any indication in any country. Safety and efficacy have not been established.

About Daiichi Sankyo
Daiichi Sankyo is an innovative global healthcare company contributing to the sustainable development of society that discovers, develops and delivers new standards of care to enrich the quality of life around the world. With more than 120 years of experience, Daiichi Sankyo leverages its world-class science and technology to create new modalities and innovative medicines for people with cancer, cardiovascular and other diseases with high unmet medical needs. For more information, please visit www.daiichisankyo.com.

Merck’s Focus on Cancer
Every day, we follow the science as we work to discover innovations that can help patients, no matter what stage of cancer they have. As a leading oncology company, we are pursuing research where scientific opportunity and medical need converge, underpinned by our diverse pipeline of more than 25 novel mechanisms. With one of the largest clinical development programs across more than 30 tumor types, we strive to advance breakthrough science that will shape the future of oncology. By addressing barriers to clinical trial participation, screening and treatment, we work with urgency to reduce disparities and help ensure patients have access to high-quality cancer care. Our unwavering commitment is what will bring us closer to our goal of bringing life to more patients with cancer. For more information, visit www.merck.com/research/oncology.

About Merck
At Merck, known as MSD outside of the United States and Canada, we are unified around our purpose: We use the power of leading-edge science to save and improve lives around the world. For more than 130 years, we have brought hope to humanity through the development of important medicines and vaccines. We aspire to be the premier research-intensive biopharmaceutical company in the world – and today, we are at the forefront of research to deliver innovative health solutions that advance the prevention and treatment of diseases in people and animals. We foster a diverse and inclusive global workforce and operate responsibly every day to enable a safe, sustainable and healthy future for all people and communities. For more information, visit www.merck.com and connect with us on X (formerly Twitter), Facebook, Instagram, YouTube and LinkedIn.

Forward-Looking Statement of Merck & Co., Inc., Rahway, N.J., USA
This news release of Merck & Co., Inc., Rahway, N.J., USA (the “company”) includes “forward-looking statements” within the meaning of the safe harbor provisions of the U.S. Private Securities Litigation Reform Act of 1995. These statements are based upon the current beliefs and expectations of the company’s management and are subject to significant risks and uncertainties. There can be no guarantees with respect to pipeline candidates that the candidates will receive the necessary regulatory approvals or that they will prove to be commercially successful. If underlying assumptions prove inaccurate or risks or uncertainties materialize, actual results may differ materially from those set forth in the forward-looking statements.

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