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The WILLOW Trial Didn't Fail Enpatoran. The Endpoint Did.
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Fusion42 · 28 September 2026 · Fusion42 review
The WILLOW Phase IIb trial of enpatoran for lupus failed to meet its primary composite endpoint due to a flawed statistical model that assumed a monotonic dose-response curve, while the drug's pharmacodynamic effect actually plateaued. This mismatch led to the trial being declared negative despite evidence that enpatoran altered disease biology, highlighting the need for endpoints tailored to targeted therapies rather than broad composites.
This Wire brief sits within Fusion42's coverage of Biotech.
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Trial designers in lupus and immunology must rewrite their endpoint approach to match targeted drugs like enpatoran. You need to push regulators for mechanistic or domain-specific measures rather than traditional composites to prove efficacy early and avoid discard.
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1 source · 28 Sep 2026
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