Merck and Daiichi Sankyo’s I-DXd Earns FDA Breakthrough Therapy Status in Small Cell Lung Cancer

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Daiichi Sankyo announced on Aug. 18, 2025 that it received breakthrough therapy designation from FDA for ifinatamab deruxtecan (I-DXd) for adults with extensive-stage small cell lung cancer whose disease has progressed following platinum-based chemotherapy. This designation, which aims to accelerate development of therapies addressing serious conditions with unmet medical need, reflects encouraging clinical data from ongoing global studies (1).

This development highlights the potential of I-DXd as a novel therapeutic option as well as the continued momentum of antibody-drug conjugate (ADC) technology, which is evolving into increasingly targeted and engineered formats.

“[FDA’s] granting of breakthrough therapy designation 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, in a company press release (1). “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.”

Clinical evidence supporting FDA decision

FDA’s decision was supported primarily by findings from a Phase II (IDeate-Lung01) trial, supplemented by data from a Phase I/II (IDeate-PanTumor01) study. The primary endpoint of the Phase II trial is objective response rate by blinded independent central review, with secondary endpoints including duration of response, progression-free survival, overall survival, and safety. Results from that Phase II trial are expected to be shared at the 2025 World Conference on Lung Cancer, which will be held on Sept. 6–9 in Barcelona. The conference will be hosted by the International Association for the Study of Lung Cancer (IASLC).

“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, MSD Research Laboratories, in the release. “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.”

Collaboration with Merck & Co.

Daiichi Sankyo entered into a global collaboration with Merck & Co., Rahway, NJ, USA (known as MSD outside of the United States and Canada) in October 2023 under which the two companies are jointly developing and commercializing several ADC assets: patritumab deruxtecan (HER3-DXd), I-DXd, and raludotatug deruxtecan (R-DXd). The development and commercialization rights apply to worldwide markets except Japan, where Daiichi Sankyo will maintain exclusive rights. Under the agreement, Daiichi Sankyo will be solely responsible for manufacturing and supply (2).

This agreement was expanded in August 2024 to include another asset, gocatamig (MK-6070/DS3280), which the companies will jointly develop and commercialize worldwide, except in Japan where Merck will maintain exclusive rights. Under the expanded agreement, Merck will be solely responsible for manufacturing and supply for gocatamig (3).

References

1. Daiichi Sankyo.Ifinatamab Deruxtecan Granted Breakthrough Therapy Designation by US FDA for Patients with Pretreated Extensive-Stage Small Cell Lung Cancer. Press Release. Aug. 18, 2025.
2. Daiichi Sankyo. Daiichi Sankyo and Merck & Co., Inc., Rahway, NJ, USA Announce Global Development and Commercialization Collaboration for Three Daiichi Sankyo DXd ADCs. Press Release. Oct. 20, 2023.
3. Daiichi Sankyo. Daiichi Sankyo and Merck & Co., Inc., Rahway, NJ, USA Enter into Global Development and Commercialization Agreement for MK-6070. Press Release. Aug. 6, 2024.