Zymeworks Inc. announced on September 2, 2025, its decision to voluntarily discontinue the clinical development of ZW171, an experimental T cell engager designed to target gynecological, thoracic, and digestive system cancers. This decision was made after results from the dose escalation portion of the Phase 1 trial indicated the treatment was unlikely to meet the company's goals as a standalone therapy.
The discontinuation was based on the determination that further dose evaluation in the current trial would not support a benefit-risk profile consistent with the desired monotherapy target product profile. While cytokine release syndrome was well-managed in the Phase 1 study, dose-limiting toxicities were observed, consistent with mesothelin-related on-target off-tumor toxicity.
Kenneth Galbraith, Chair and Chief Executive Officer of Zymeworks, stated that this decision is part of the company's disciplined approach to portfolio management, ensuring resources are directed towards product candidates with the greatest potential impact. Zymeworks will continue to advance its broader product pipeline, including the ongoing Phase 1 trial of ZW191, the initiation of a Phase 1 study for ZW251 expected in 2025, and preparations for an IND filing for ZW209 in the first half of 2026.
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