Merck Shares Edge Up 0.01% on FDA Breakthrough Designation for Cancer Drug Despite 124th-Ranked $0.7B Trading Volume

On August 18, 2025, Merck (MRK) closed with a 0.01% gain, trading at a volume of $0.70 billion—a 20.8% decline from the prior day—ranking 124th in market activity. The stock’s muted movement came amid a key regulatory development for its joint oncology candidate.

Ifinatamab deruxtecan, a B7-H3 directed antibody-drug conjugate co-developed by Merck and Daiichi Sankyo, received Breakthrough Therapy Designation (BTD) from the FDA for treating extensive-stage small cell lung cancer (SCLC) in patients who progressed after platinum-based chemotherapy. This marks the first BTD for the collaboration and follows positive Phase 2 IDeate-Lung01 trial data, which will be presented at the IASLC 2025 conference. The designation underscores the potential of the drug to address a significant unmet need in SCLC, a disease with limited therapeutic options and poor survival rates.

Merck’s oncology division emphasized the milestone as a validation of the compound’s clinical promise. The BTD accelerates regulatory pathways, potentially expediting approval timelines. The drug’s mechanism targets B7-H3, a protein overexpressed in aggressive cancers, and has shown encouraging safety and efficacy in earlier trials. With Daiichi Sankyo handling manufacturing and supply, the partnership aims to advance ifinatamab deruxtecan toward commercialization, aligning with Merck’s broader strategy to expand its oncology portfolio through innovative therapies.

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