Zymeworks Stock Soars 30% on Positive Cancer Drug Trial Results
Phase 3 data for zanidatamab, partnered with Jazz Pharmaceuticals, shows significant improvement in treating gastroesophageal adenocarcinoma, paving way for regulatory submission.
Shares of Zymeworks Inc. (NASDAQ: ZYME) surged nearly 30% in morning trading after the company announced positive topline results from a pivotal Phase 3 trial of its flagship cancer drug, zanidatamab. The successful trial is a major validation for the biotechnology firm and its partner, Jazz Pharmaceuticals (NASDAQ: JAZZ), which also saw its stock climb over 21% on the news.
The HERIZON-GEA-01 study evaluated zanidatamab in patients with previously untreated HER2-positive gastroesophageal adenocarcinoma (GEA), a form of cancer with historically limited treatment options. The results showed that regimens including zanidatamab delivered "highly statistically significant and clinically meaningful improvements" in progression-free survival compared to the current standard of care, which consists of trastuzumab plus chemotherapy.
Zymeworks stock jumped $5.49 to $24.01, hitting a new 52-week high and pushing its market capitalization to approximately $1.39 billion. The heavy trading volume underscored investor enthusiasm for the results, which position zanidatamab as a potential new cornerstone therapy in a competitive oncology market.
A New Standard of Care
The trial tested two zanidatamab-based regimens. The first, combining the drug with standard chemotherapy, met its primary endpoint for progression-free survival (PFS) and showed a strong, positive trend in overall survival (OS). The second combination, which added the checkpoint inhibitor tislelizumab to zanidatamab and chemotherapy, demonstrated statistically significant improvements in both PFS and overall survival.
"The topline results from HERIZON-GEA-01 represent a true turning point for patients with HER2+ gastroesophageal adenocarcinoma," said Kenneth Galbraith, Chairman and CEO of Zymeworks, in a company press release. "These data highlight the potential of zanidatamab to transform the standard of care in HER2+ indications."
Zanidatamab is a bispecific antibody that targets two separate domains of the HER2 protein, a key driver of tumor growth in some cancers. This novel mechanism is believed to provide a more potent and durable anti-tumor response compared to existing HER2-targeted therapies like trastuzumab.
The current global market for HER2-positive gastric cancer is estimated to be over $222 million annually, with analysts projecting steady growth as new therapies emerge. The success of zanidatamab could significantly expand this market and capture a substantial share for Zymeworks and Jazz.
The Path to Market
Following the positive data, Jazz Pharmaceuticals announced its intention to submit a supplemental Biologics License Application (sBLA) to the U.S. Food and Drug Administration (FDA) in the first half of 2026. This filing will seek approval for zanidatamab as a first-line treatment for patients with this type of advanced GEA.
The partners also plan to present the full data set from the HERIZON-GEA-01 study at a major medical conference in early 2026 and publish the findings in a peer-reviewed journal. While the company confirmed the trial's success, specific data points such as hazard ratios and p-values were not disclosed in the initial announcement and will be a key focus for clinicians and investors when the full results are presented.
The positive outcome is a significant de-risking event for Zymeworks, whose pipeline is heavily reliant on its proprietary drug development platforms. For Jazz Pharmaceuticals, which acquired the rights to commercialize zanidatamab, the results provide a clear path toward a potential blockbuster therapy that diversifies its oncology portfolio. The strong market reaction for both companies reflects the drug's potential to meaningfully improve patient outcomes and generate significant future revenue.