FDA approves Ziihera for first-line HER2-positive gastroesophageal adenocarcinoma, triggering milestones and $250 million Royalty Pharma financing

The FDA on August 25, 2026 approved Ziihera (zanidatamab-hrii) for first-line unresectable locally advanced or metastatic HER2-positive gastroesophageal adenocarcinoma: IHC 3+ and IHC 2+/ISH+ patients can receive it with tislelizumab plus chemotherapy, and IHC 3+ patients with chemotherapy alone. Under the BeOne Medicines collaboration, Zymeworks has received $81 million, with up to $144 million in further milestones and tiered royalties of up to 19.5%. The approval triggers the structure set up on March 2, 2026, when Zymeworks BC moved 30% of future Ziihera royalties into Zymeworks Royalty Limited Partnership, which borrowed $250 million in non-recourse notes from Royalty Pharma secured solely on those royalties.