Daiichi Sankyo (TSE: 4568) and Merck (NYSE: MRK), known as MSD outside of the United States and Canada, today announced positive results from the Phase 2 IDeate-Lung01 trial of ifinatamab deruxtecan (I-DXd) in patients with previously treated extensive-stage small cell lung cancer (ES-SCLC). Findings were presented during a late-breaking oral session (OA06.03) at the 2025 World Conference on Lung Cancer (#WCLC25) and featured in the congress press program.

Ifinatamab deruxtecan is a specifically engineered, potential first-in-class B7-H3 directed DXd antibody drug conjugate (ADC) discovered by Daiichi Sankyo and jointly developed with Merck. In August 2025, the U.S. Food and Drug Administration (FDA) granted Breakthrough Therapy Designation for I-DXd in ES-SCLC patients whose disease has progressed on or after platinum-based chemotherapy.

In the trial, I-DXd demonstrated a confirmed objective response rate (ORR) of 48.2% (95% CI: 39.6–56.9) among 137 patients, as assessed by blinded independent central review (BICR). Responses included three complete responses (CRs) and 63 partial responses (PRs), with a disease control rate (DCR) of 87.6% and median duration of response (DOR) of 5.3 months. Median progression-free survival (PFS) was 4.9 months and median overall survival (OS) was 10.3 months.

Notably, in a subset of patients treated in the second-line setting (n=32), the ORR was 56.3% with a median DOR of 7.2 months and OS of 12.0 months. In patients treated in third-line and beyond settings (n=105), the ORR was 45.7% with three CRs and 45 PRs reported. An exploratory analysis also showed an intracranial ORR of 46.2% in patients with brain metastases at baseline.

“Patients with extensive-stage small cell lung cancer face a poor prognosis despite current standard therapies,” said Myung-Ju Ahn, MD, PhD, Professor of Hematology & Oncology at Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul. “The strong responses seen in IDeate-Lung01 highlight the promise of ifinatamab deruxtecan as a new treatment approach.”

The safety profile of I-DXd was consistent with prior studies, with no new safety signals identified. Grade 3 or higher treatment-related adverse events occurred in 36.5% of patients, the most common being neutropenia (13.9%), lymphopenia (12.4%) and anemia (10.2%). Interstitial lung disease (ILD)/pneumonitis was observed in 12.4% of patients, with most cases low grade.

“These results reinforce the potential of ifinatamab deruxtecan for patients with ES-SCLC who have exhausted prior treatment options,” said Ken Takeshita, MD, Global Head, R&D, Daiichi Sankyo. “They will support our ongoing regulatory discussions worldwide.”

“With limited advances in small cell lung cancer over the past three decades, the need for new treatment approaches is critical,” said Eliav Barr, MD, Senior Vice President, Head of Global Clinical Development and Chief Medical Officer, Merck Research Laboratories. “Ifinatamab deruxtecan represents an important innovation that could bring hope to patients living with this aggressive disease.”

A majority of patients in the study (54.7%) had received two or more prior lines of treatment, including immunotherapy, topoisomerase I inhibitors, and DLL3-targeted therapies. As of data cutoff (March 3, 2025), 14 patients remain on treatment.