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After missed endpoint, Gossamer and Chiesi pull the plug on PAH drug collaboration
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Fusion42 · 27 July 2026 · Fusion42 review
Gossamer Bio has terminated its $486 million collaboration with Chiesi on the PAH drug seralutinib, regaining worldwide rights after the candidate missed its primary endpoint in phase 3 but showed secondary efficacy signals. The company plans to file an NDA with the FDA in September based on the trial data and a pre-NDA meeting characterization that positioned statistical significance as a review issue rather than a filing barrier.
This Wire brief sits within Fusion42's coverage of Biotech.
◆ ◆ The Wire takeaway
Gossamer has discovered the FDA will accept a missed primary endpoint if secondary data shows the drug works in a harder subgroup. If you're building a rare disease therapy that fails its primary but shows real activity in a subset, the regulatory path just opened—talk to your FDA contact about how to frame subgroup efficacy as a filing strength, not a weakness.
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1 source · 27 Jul 2026
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