A Biologics License Application (BLA) for ifinatamab deruxtecan in extensive-stage small cell lung cancer (ES-SCLC) has been voluntarily withdrawn after discussions with the US FDA concluded that the available Phase II data were insufficient to support accelerated approval, removing a near-term regulatory route for the Daiichi Sankyo (TSE: 4568) and Merck (NYSE: MRK) antibody-drug conjugate (ADC).
The filing covered adults whose disease had progressed on or after platinum-based chemotherapy and was supported by the Phase II IDeate-Lung01 study. The 187-patient trial evaluated 8 mg/kg and 12 mg/kg doses of ifinatamab deruxtecan, with objective response rate by blinded independent review as the primary endpoint. Daiichi Sankyo and Merck did not disclose which elements of the efficacy package the FDA considered insufficient to support accelerated approval. The withdrawal follows earlier regulatory momentum for the program, including Breakthrough Therapy Designation in August 2025 and Priority Review in April 2026.
The withdrawal reverses a series of regulatory advances: the US FDA had granted Breakthrough Therapy Designation for the ES-SCLC indication in August 2025, followed by Priority Review in April 2026.
Ifinatamab deruxtecan is a B7-H3-directed antibody-drug conjugate (ADC) comprising a humanized anti-B7-H3 IgG1 monoclonal antibody linked to a topoisomerase I inhibitor payload — an exatecan derivative designated DXd — via tetrapeptide-based cleavable linkers, using Daiichi Sankyo's proprietary DXd ADC technology platform. B7-H3 is a transmembrane protein overexpressed across multiple cancer types including SCLC, castration-resistant prostate cancer (CRPC), and esophageal squamous cell carcinoma (ESCC), and its overexpression has been associated with poor prognosis.