Zymeworks Shares Surge 29.05 on Landmark HER2 Trial Results Trading Volume Hits $280M Ranking 415th in U.S. Dollar Volume

Market Snapshot

On November 17, 2025, Zymeworks Inc. , . stocks. The rally followed the release of positive topline results from the Phase 3 HERIZON-GEA-01 trial for Ziihera (zanidatamab-hrii) in first-line HER2-positive gastroesophageal adenocarcinoma (GEA). , reflecting strong investor optimism ahead of the official market open.

Key Drivers

The stock’s sharp rise was catalyzed by the successful Phase 3 trial results for Ziihera, which demonstrated statistically significant improvements in progression-free survival (PFS) and overall survival (OS) compared to the current standard of care. Both Ziihera + chemotherapy and Ziihera + Tevimbra (tislelizumab) + chemotherapy outperformed trastuzumab + chemotherapy, with the triple-combination regimen showing a statistically significant OS benefit. The trial’s success positions Ziihera as a potential new standard of care in first-line HER2-positive GEA, a high-need oncology indication with limited treatment options.

Jazz Pharmaceuticals, Zymeworks’ development partner, announced plans to file a supplemental Biologics License Application (sBLA) in the first half of 2026, accelerating Ziihera’s path to regulatory approval. The data also highlighted consistent efficacy across PD-L1 subgroups, simplifying biomarker-driven treatment decisions and broadening the drug’s applicability. Additionally, Ziihera’s safety profile remained aligned with known risks, with no new safety signals observed, reinforcing its potential for rapid adoption.

The market reaction was further amplified by Zymeworks’ recent Q3 2025 financial report, , providing operational runway through the second half of 2027. While the company continues to report net losses, the revenue growth and robust cash position signaled improved financial stability. Analysts noted that the HERIZON-GEA-01 results could unlock additional milestone and royalty payments from partners Jazz and BeOne Medicines, potentially boosting Zymeworks’ top-line growth.

However, risks remain. Regulatory approval is not guaranteed, and competitors in HER2-positive GEA, including established HER2-targeted therapies and newer antibody-drug conjugates, could limit Ziihera’s market share. Additionally, Zymeworks’ reliance on partners for commercialization introduces execution risks, as Jazz and BeOne will drive regulatory submissions and market access. The company’s ongoing cash burn and high R&D costs also pose challenges, despite its strong balance sheet.

The broader oncology pipeline, including early-stage ADC programs like ZW191 and ZW251, adds long-term value potential but carries development risks. Zymeworks’ decision to discontinue ZW171 in September 2025 underscores its focus on high-impact programs, but the success of Ziihera remains critical to funding future development.

In summary, Zymeworks’ stock surge reflects investor confidence in Ziihera’s clinical and commercial potential, supported by robust trial data and strategic partnerships. While regulatory and competitive hurdles persist, the HERIZON-GEA-01 results represent a pivotal milestone for the company, positioning it to capture a significant share of the HER2-positive GEA market if Ziihera secures approval.