US pharmaceutical company Merck & Co Inc (NYSE:MRK), known as MSD outside the US and Canada, and Japanese healthcare company Daiichi Sankyo Co Ltd (TYO:4568) announced on Monday that the US Food and Drug Administration (FDA) has granted Priority Review to the Biologics License Application for ifinatamab deruxtecan for adult patients with extensive-stage small cell lung cancer after progression on platinum-based chemotherapy.

Ifinatamab deruxtecan is a specifically engineered, potential first-in-class B7-H3 directed DXd antibody drug conjugate (ADC) discovered by Daiichi Sankyo and being jointly developed by Daiichi Sankyo and Merck.

The submission is supported by results from the IDeate-Lung01 Phase 2 trial, with additional support from the IDeate-PanTumor01 Phase 1/2 study. The FDA action date for its regulatory decision is 10 October 2026.

Additionally, the FDA is reviewing the application under the Real-Time Oncology Review program and Project Orbis to accelerate oncology evaluation pathways.

Ifinatamab deruxtecan previously received Breakthrough Therapy Designation in August 2025 and has also been granted Orphan Drug Designation in multiple jurisdictions for small cell lung cancer and oesophageal cancer.

The broader clinical development programme includes Phase 3 studies in small cell lung cancer, castration-resistant prostate cancer, and oesophageal squamous cell carcinoma.