Zymeworks Inc. (ZYME), a biotechnology company, announced positive efficacy and safety results from its Phase 3 HERIZON-GEA-01 trial evaluating Ziihera (zanidatamab-hrii) in HER2-positive locally advanced or metastatic gastroesophageal adenocarcinoma.
HERIZON-GEA-01 is a randomised, open-label Phase 3 trial wherein participants were randomized to one of three treatment arms: Ziihera in combination with chemotherapy; Ziihera combined with both chemotherapy and tislelizumab; or the control regimen consisting of trastuzumab plus chemotherapy. The study involved 914 patients and is being conducted jointly by Jazz and BeOne Medicines.
Patients were randomised to three trial arms based on the combination, to evaluate two primary endpoints, namely progression-free survival per blinded independent central review and overall survival.
The positive results of HERIZON-GEA-01 included a greater than four-month improvement in median progression-free survival (PFS) prolongation compared to the control arm for Ziihera plus tislelizumab and chemotherapy and Ziihera plus chemotherapy, a greater than seven-month improvement in median overall survival or OS and a 28% reduction in the risk of death versus trastuzumab plus chemotherapy.
The data will be presented at the oral presentation at the 2026 ASCO Gastrointestinal Cancers Symposium in San Francisco on January 8, 2026, from 8:57- 9:07 am PST.
In addition, under the existing arrangements with Jazz and BeOne Medicines, Zymeworks is eligible to receive up to $440.0 million in near-term milestone payments, to be earned upon regulatory approvals of Ziihera in gastroesophageal adenocarcinoma in the United States, Europe, Japan, and China.
Gastroesophageal adenocarcinoma, which includes cancers of the stomach, gastroesophageal junction, and oesophagus, is the fifth most common cancer worldwide, and approximately 20% of patients have HER2+ disease. HER2 is a protein that helps control cell growth, and when it is overexpressed, it makes cancer cells multiply rapidly.
During this first interim analysis, Ziihera plus chemotherapy showed a median OS of more than two years, with statistical significance, favouring Ziihera plus chemotherapy versus trastuzumab plus chemotherapy.
An additional planned OS interim analysis for Ziihera plus chemotherapy is currently expected in mid-2026.
ZYME closed Tuesday's trade 5.10% down at $24.18. In the after-hours market, ZYME traded 0.37% down at $24.09.
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