Merck & Co. and Daiichi Sankyo announced that the U.S. Food and Drug Administration has granted priority review status to their antibody‑drug conjugate ifinatamab deruxtecan (I‑DXd) for patients with extensive‑stage small cell lung cancer (ES‑SCLC) who have progressed after platinum‑based chemotherapy. The designation signals the agency’s intent to accelerate the review process, potentially shortening the time to approval and market launch.
The priority review is a strategic win for Merck’s oncology portfolio. It positions I‑DXd as a promising first‑in‑class B7‑H3 directed ADC in a high‑need area and provides a new growth engine ahead of the Keytruda patent cliff, which is expected to expire in the United States around 2028‑2029. A faster approval could allow Merck to capture market share before competitors introduce similar ADCs.
I‑DXd is built on a novel antibody‑drug conjugate platform that delivers a topoisomerase I inhibitor directly to B7‑H3‑expressing tumor cells. The U.S. Biologics License Application is supported by data from the IDeate‑Lung01 Phase 2 trial and the IDeate‑PanTumor01 Phase 1/2 study. The drug previously received Breakthrough Therapy designation in August 2025, and the global collaboration between Merck and Daiichi Sankyo was formalized in October 2023.
Small cell lung cancer accounts for roughly 27,000 new U.S. cases in 2025, representing about 12% of all lung cancers. The ADC market, valued at $10 billion in 2023, is projected to reach $39 billion by 2030, underscoring the commercial potential of I‑DXd. The partnership leverages Daiichi Sankyo’s ADC expertise and Merck’s oncology pipeline, creating a synergistic platform that could accelerate development of additional ADC candidates.
"The FDA’s granting of Priority Review for ifinatamab deruxtecan marks a significant milestone in our effort to provide new and innovative treatment options for patients with extensive‑stage small cell lung cancer," said Dr. John Tsai, Global Head of R&D at Daiichi Sankyo. "We look forward to continuing to work with the FDA to bring this potential first‑in‑class B7‑H3 directed DXd antibody‑drug conjugate to patients as quickly as possible."
"Small cell lung cancer remains one of the toughest cancers to treat, with few options if the disease progresses after standard of care treatments. The FDA’s acceptance of the BLA reinforces the important role that ifinatamab deruxtecan could play in helping to address the needs of patients with extensive‑stage small cell lung cancer," said Dr. Eliav Barr, Senior Vice President, Head of Global Clinical Development and Chief Medical Officer at Merck Research Laboratories.
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