Ziihera combinations show over two years median overall survival in first‑line HER2+ metastatic GEA

Phase 3 HERIZON‑GEA‑01 reported that Ziihera plus tislelizumab and chemotherapy achieved a median overall survival of 26.4 months, and both Ziihera combinations improved progression‑free survival versus trastuzumab plus chemotherapy.

Zymeworks and its partners reported positive Phase 3 HERIZON‑GEA‑01 results for Ziihera (zanidatamab‑hrii) combinations as first‑line therapy for adults with HER2‑positive locally advanced or metastatic gastroesophageal adenocarcinoma (GEA). The company announced improved progression‑free survival for both investigational Ziihera arms versus trastuzumab plus chemotherapy, and a median overall survival of 26.4 months for the Ziihera plus tislelizumab and chemotherapy arm. These findings are being presented as a late‑breaking oral presentation at the 2026 ASCO Gastrointestinal Cancers Symposium on January 8, 2026. The trial randomized 914 patients across approximately 300 sites in over 30 countries. Key findings: - Ziihera plus tislelizumab and chemotherapy was reported to have a median overall survival of 26.4 months, described as a greater than seven‑month improvement versus trastuzumab plus chemotherapy and reported as a 28% reduction in the risk of death. - Both Ziihera investigational arms were reported to reduce the risk of disease progression or death by about 35% versus trastuzumab plus chemotherapy, with a median progression‑free survival of more than one year (about a four‑month improvement versus control). - At the first interim OS analysis, Ziihera plus chemotherapy showed a median overall survival of more than two years and a strong trend favoring that arm; an additional planned OS interim analysis for Ziihera plus chemotherapy is expected in mid‑2026. - The safety profile was reported as consistent with known effects of HER2‑directed therapy and immunotherapy, with Grade ≥3 treatment‑related adverse event rates of 71.8% (Ziihera+tislelizumab+chemo), 59.0% (Ziihera+chemo), and 59.6% (trastuzumab+chemo). - The most common Grade ≥3 treatment‑related adverse event was diarrhea, reported at 24.5% (Ziihera+tislelizumab+chemo), 20.0% (Ziihera+chemo), and 12.9% (trastuzumab+chemo); discontinuation due to treatment‑related diarrhea was reported as uncommon. Summary: The article presents HERIZON‑GEA‑01 as showing clinically meaningful improvements in progression‑free survival for both Ziihera combinations and a reported median overall survival of 26.4 months for the Ziihera plus tislelizumab and chemotherapy arm. The data will be presented at ASCO‑GI on January 8, 2026, and an additional OS interim analysis for the Ziihera plus chemotherapy arm is planned for mid‑2026. The article also states that Zymeworks is eligible to receive up to $440.0 million in milestone payments tied to potential regulatory approvals in several regions.