Zymeworks’ HER2‑targeted bispecific zanidatamab (Ziihera) achieved its primary endpoint in the Phase III HERIZON‑GEA‑01 trial, demonstrating significant progression‑free survival (PFS) gains versus trastuzumab plus chemotherapy in first‑line HER2‑positive gastroesophageal adenocarcinoma. The Ziihera combinations also showed clinically meaningful overall survival trends at interim analysis. Jazz Pharmaceuticals, Zymeworks’ commercialization partner, signaled intent to submit supplemental applications based on the data. The results strengthen zanidatamab’s positioning as a potential new standard for HER2‑positive GEA and set the stage for regulatory filings in multiple regions. The trial victory amplifies interest in bispecific HER2 agents and will prompt payers and guideline committees to consider sequencing and combination strategies in a disease area with high unmet need.