Zymeworks and partners Jazz Pharmaceuticals and BeOne announced positive topline results from the Phase 3 HERIZON‑GEA‑01 trial: zanidatamab (Ziihera) plus chemotherapy improved progression‑free survival versus trastuzumab plus chemotherapy, and the triplet with tislelizumab produced statistically significant overall survival and PFS gains. Jazz said it will file a supplemental BLA in the first half of 2026 based on the data. The trial compared two zanidatamab regimens — zanidatamab plus chemo, and zanidatamab plus PD‑1 inhibitor Tevimbra (tislelizumab) plus chemo — to the trastuzumab/chemo control in first‑line HER2‑positive gastroesophageal adenocarcinoma. Both zanidatamab arms showed clinically meaningful PFS improvement; the triplet achieved statistically significant OS benefit at the first interim analysis. Partners highlighted the potential for zanidatamab to become a new standard HER2 agent in first‑line disease and indicated regulatory submissions will follow. The result strengthens the commercial and clinical rationale for bispecific HER2 targeting in gastroesophageal cancers and sets up regulatory and payer decisions relevant to first‑line oncology treatment sequencing.