Zymeworks, together with development partner Jazz Pharmaceuticals, announced positive topline results from the Phase III HERIZON-GEA-01 trial of the HER2-directed bispecific zanidatamab in first-line HER2-positive gastroesophageal adenocarcinoma (GEA). Both zanidatamab-plus-chemotherapy arms showed statistically significant and clinically meaningful improvements in progression-free survival versus trastuzumab plus chemotherapy; the triplet with PD-1 inhibitor tislelizumab also demonstrated significant overall survival gains. The data support zanidatamab as a potential new standard of care in first-line HER2+ GEA and prompted Jazz to prepare a supplemental biologics filing in the first half of 2026. Results include improvements in PFS across comparator arms and a clinically meaningful OS benefit in the PD-1 combination arm at the first OS analysis. If regulators accept the data, zanidatamab could shift prescribing in a high-unmet-need tumor type and validate bispecific HER2-targeting approaches in gastroesophageal cancers, with downstream implications for commercial partnerships and sequencing in HER2-directed care.