Zymeworks and partners Jazz Pharmaceuticals and BeOne announced positive topline results from the Phase 3 HERIZON‑GEA‑01 trial testing zanidatamab (Ziihera) with chemotherapy, with and without PD‑1 inhibitor tislelizumab. Both Ziihera arms met primary progression‑free survival endpoints; the triplet (Ziihera + tislelizumab + chemo) also showed statistically significant overall survival improvements versus trastuzumab plus chemotherapy. Jazz said it plans a supplemental Biologics License Application submission in 1H 2026 based on the data. The results strengthen zanidatamab’s positioning as a potential new first‑line HER2 agent in gastroesophageal adenocarcinoma and could reallocate commercial and regulatory plans across partners.