Zymeworks Reports Positive HERIZON-GEA-01 Trial Results

Zymeworks announced "positive" efficacy and safety results from the Phase 3 HERIZON-GEA-01 trial evaluating Ziihera in combination with chemotherapy, with or without the PD-1 inhibitor Tevimbra, as first-line treatment for adults with HER2-positive locally advanced or metastatic gastroesophageal adenocarcinoma, including cancers of the stomach, gastroesophageal junction and esophagus. The data will be presented as a late-breaking oral presentation at the 2026 ASCO Gastrointestinal Cancers Symposium in San Francisco on January 8, the company noted. The study found: Both investigational arms, Ziihera plus tislelizumab and chemotherapy and Ziihera plus chemotherapy, led to a statistically significant and clinically meaningful prolongation of progression-free survival with approximately 35% reduction in the risk of disease progression or death versus trastuzumab plus chemotherapy. This resulted in a median PFS of more than one year, representing a greater than four month improvement compared to the control arm; Ziihera plus tislelizumab and chemotherapy demonstrated a statistically significant and clinically meaningful overall survival benefit with a median OS of more than two years (26.4 months), the longest reported in a Phase 3 trial in GEA, representing a greater than seven-month improvement in median OS and a 28% reduction in the risk of death versus trastuzumab plus chemotherapy; At this first interim analysis, Ziihera plus chemotherapy showed a median OS of more than two years, with a strong trend toward statistical significance, favoring Ziihera plus chemotherapy versus trastuzumab plus chemotherapy. An additional planned OS interim analysis for Ziihera plus chemotherapy is currently expected in mid-2026; The OS and PFS benefits were generally consistent across major prespecified subgroups including geographic region and PD-L1 status for both investigational arms. "These results underscore the promise of zanidatamab to meaningfully advance care for patients with HER2-positive disease. They also reflect the power of our Azymetric platform to generate highly differentiated, multifunctional biologics and validate our partnership-driven approach with Jazz and BeOne to efficiently deliver innovative therapies on a global scale. Importantly, the HERIZON-GEA-01 data further establish Ziihera as the new HER2-targeted agent-of-choice in first-line locally advanced or metastatic HER2-positive GEA with the potential to redefine first-line treatment for patients in this setting. Alongside continued progress across Jazz and BeOne's broader development efforts, these data reinforce our belief in Ziihera's potential across a range of HER2-expressing solid tumors. We look forward to Jazz and BeOne moving rapidly towards global regulatory submissions based on the HERIZON-GEA-01 data," said Kenneth Galbraith, Chair and Chief Executive Officer of Zymeworks.