Partners Zymeworks, Jazz Pharmaceuticals and BeOne Medicines announced positive topline results from the Phase III HERIZON‑GEA‑01 trial: zanidatamab (Ziihera) plus chemotherapy improved progression‑free survival versus trastuzumab plus chemotherapy in first‑line HER2‑positive gastroesophageal adenocarcinoma. The zanidatamab plus tislelizumab arm also showed statistically significant overall survival and PFS gains. The trial’s findings, released by Zymeworks and Jazz, support submissions to regulators — Jazz expects a supplemental BLA filing in H1 2026 — and reposition zanidatamab as a potential new HER2‑targeted standard of care in GEA. Results were reported across key endpoints and will drive near‑term regulatory and commercial planning. Investors reacted with sharp share moves as the data recast the value of the Jazz‑Zymeworks collaboration and strengthened expectations for future royalty and milestone flows. The dataset will be scrutinized for durability, safety, and subgroup consistency as regulatory filings proceed.