FDA approves Ziihera in two regimens for first-line HER2+ gastroesophageal cancer

The FDA has approved two Ziihera (zanidatamab-hrii)-containing regimens for adults with unresectable locally advanced or metastatic HER2-positive gastroesophageal adenocarcinoma, Zymeworks announced on August 25, 2026. The approvals cover Ziihera plus Tevimbra (tislelizumab-jsgr) and chemotherapy for patients with HER2+ IHC 3+ and IHC 2+/ISH+ disease regardless of PD-L1 status, and Ziihera plus chemotherapy alone for IHC 3+ patients.¹

Zymeworks said this marks the second FDA approval for zanidatamab in less than two years, which it said validates its Azymetric bispecific antibody platform.¹

The approval is supported by the Phase 3 trial known as HERIZON-GEA-01, which tested zanidatamab combined with immunotherapy and chemotherapy as a first-line treatment for HER2+ GEA.¹ Results were published in the New England Journal of Medicine and first presented at ASCO GI 2026.¹ The trial is continuing, with additional analyses planned.¹

Jaffer A. Ajani, M.D. of MD Anderson Cancer Center, an investigator on the trial, said the regimen produced a "median overall survival of more than two years," which he called encouraging progress for patients, and noted that similar outcomes were observed regardless of PD-L1 status, suggesting the regimen may serve a broad range of HER2-positive patients.¹

On the financial terms, Zymeworks has earned a $250 million milestone payment from Jazz Pharmaceuticals under their license agreement, bringing total payments received from Jazz to $650 million.¹ The company remains eligible for up to $1.3 billion in further regulatory and commercial milestones, plus tiered royalties ranging from 10% to 20% on Jazz's net sales in its licensed territories.¹ Separately, Zymeworks has received $81 million in upfront and milestone payments to date from its collaboration with BeOne Medicines, and remains eligible for up to $144 million more in milestones plus royalties of up to 19.5% on net sales in BeOne's territories.¹