Daiichi Sankyo and Merck Accelerate Phase 3 Trial of Ifinatamab Deruxtecan for Small Cell Lung Cancer
Confirmatory Clinical Trial for B7-H3 ADC
Daiichi Sankyo (4568.T) and Merck & Co. (MRK) are conducting the global Phase 3 IDeate-Lung02 (NCT06203210) trial to evaluate ifinatamab deruxtecan (I-DXd, DS-7300) in patients with recurrent small cell lung cancer (SCLC) who have failed prior therapy. Approximately 540 patients will be randomized 1:1 to receive I-DXd at 12 mg/kg every three weeks or physician's choice of therapy. The co-primary endpoints are objective response rate (ORR) and overall survival (OS), designed to demonstrate both tumor shrinkage and survival benefit for regulatory approval.
Drug Structure and Clinical Rationale
I-DXd is a B7-H3 (CD276)-targeting antibody-drug conjugate (ADC) currently in development without a formal brand name. It binds to tumor cells and delivers the topoisomerase I inhibitor payload, DXd. In the interim analysis of the Phase 2 IDeate-Lung01 trial, the ORR for the 12 mg/kg group was 54.8% in 42 patients, with a median OS of 11.8 months, while the 8 mg/kg group of 46 patients had ORRs of 26.1% and median OS of 9.4 months. This difference in efficacy between the two doses is the rationale for selecting the 12 mg/kg dose in the Phase 3 trial. In addition to efficacy, managing the safety profile of the DXd class, including interstitial lung disease/pneumonitis and myelosuppression, will be critical for commercial success.
Intensified Competition in Second-Line Therapy
The comparator arm consists of topotecan, amrubicin, and zepzelca (lurbinectedin), reflecting real-world clinical practice. The FDA granted accelerated approval for Zepzelca on June 15, 2020, with an ORR of 35% and a median duration of response of 5.3 months. Amgen's (AMGN) Imdelltra (tarlatamab-dlle), a DLL3-targeting bispecific T-cell engager, received accelerated approval on May 16, 2024, followed by full approval on November 19, 2025. Therefore, I-DXd must compete not only with chemotherapy but also with new immunotherapy standards.
Regulatory and Commercial Significance
The FDA granted Breakthrough Therapy Designation to I-DXd on August 18, 2025, for patients with extensive-stage SCLC who have progressed after platinum-based chemotherapy. This indicates that the regulatory agency recognizes the response rate and unmet medical need demonstrated in the IDeate-Lung01 trial. However, the OS results from the Phase 3 trial will be the key determinant of the clinical value. Zepzelca's net product sales in 2025 were $307.3 million, a 4% decrease year-over-year, reflecting the impact of Imdelltra's entry on the second-line therapy market. Therefore, if I-DXd can translate its high response rate into improved survival, it will strengthen Daiichi Sankyo and Merck's leading position in the B7-H3 ADC class and expand the potential of the DXd platform.
If I-DXd meets the co-primary endpoints of ORR and OS in the approximately 540-patient Phase 3 trial, Daiichi Sankyo (4568.T) and Merck (MRK) will secure a leading position in the B7-H3 ADC class. In the short term, the key value drivers are the management of interstitial lung disease/pneumonitis and myelosuppression associated with the 12 mg/kg dose, and demonstrating superior survival compared to topotecan, amrubicin, and Zepzelca. The benchmark for success has been raised with the FDA's full approval of Amgen's (AMGN) Imdelltra in 2025, and Zepzelca's $307.3 million in sales in 2025 demonstrates the proven commercial demand in the recurrent SCLC market. For researchers, the correlation between B7-H3 expression and efficacy will inform biomarker strategies, and for the industry, success will provide a basis for expanding the DXd payload to other B7-H3-high solid tumors.
Source: ClinicalTrials.gov (api_ct)