Zymeworks and partners Jazz Pharmaceuticals and BeOne reported positive top‑line results from the HERIZON‑GEA‑01 Phase III trial: zanidatamab (Ziihera) plus chemotherapy improved progression‑free survival versus trastuzumab plus chemotherapy in first‑line HER2‑positive gastroesophageal adenocarcinoma. The combination of zanidatamab, PD‑1 inhibitor tislelizumab (Tevimbra) and chemotherapy also delivered statistically significant overall‑survival gains. Jazz said it will pursue regulatory filings, with a supplemental biologics license application expected in first‑half 2026 for certain registrational paths. The data, which show a clinically meaningful advantage over the longstanding trastuzumab backbone, could reset the HER2 treatment standard in GEA and accelerate commercialization plans across partners. Sources: company topline releases and trial readouts.