Jazz Pharmaceuticals (NASDAQ: JAZZ) and Zymeworks (NASDAQ: ZYME) Received FDA Approval Tuesday August 25, 2026 for Ziihera (Zanidatamab-Hrii, an Anti-HER2 Bispecific Monoclonal Antibody) in Combination Regimens (With and Without Tislelizumab Plus Chemotherapy) for First-Line Treatment of Adult Patients With HER2-Positive (IHC 3+) Unresectable Locally Advanced or Metastatic Gastric, Gastroesophageal Junction, or Esophageal Adenocarcinoma (GEA); The Approval Was Based on the Phase 3 HERIZON-GEA-01 Trial Documenting Median Overall Survival of More Than Two Years, and Triggers a $250 Million Milestone Payment From Jazz to Zymeworks With Zymeworks Remaining Eligible for Up to $1.3 Billion in Additional Milestones Plus Tiered Royalties of Up to 20% on Net Sales
Jazz Pharmaceuticals (NASDAQ: JAZZ) and Zymeworks (NASDAQ: ZYME) received FDA approval Tuesday August 25, 2026 for Ziihera (zanidatamab-hrii, an anti-HER2 bispecific monoclonal antibody) in combination regimens for first-line treatment of adult patients with HER2-positive (IHC 3+) unresectable locally advanced or metastatic gastric, gastroesophageal junction, or esophageal adenocarcinoma (GEA). Approved regimens: Ziihera with chemotherapy (fluoropyrimidine and platinum), and Ziihera with tislelizumab (BeiGene's anti-PD-1 monoclonal antibody) plus chemotherapy. Trial basis: Phase 3 HERIZON-GEA-01 documented median overall survival of more than two years. Ziihera mechanism: zanidatamab-hrii is a bispecific antibody that binds two distinct epitopes on HER2 simultaneously, producing higher-affinity target engagement, receptor clustering, and immune-mediated tumor cell killing versus conventional monospecific anti-HER2 antibodies. The approval triggers a $250 million milestone payment from Jazz to Zymeworks, with Zymeworks remaining eligible for up to $1.3 billion in additional milestones plus tiered royalties of up to 20% on net sales. Jazz expects to launch Ziihera commercially in the US in this indication. The approval extends the Ziihera commercial franchise beyond its earlier accelerated approval in biliary tract cancer to a substantially larger commercial indication in HER2-positive GEA. GEA is a globally common cancer with roughly 22,000 US cases per year and substantially higher incidence in Asia; roughly 15-25% of GEA cases express HER2, defining the addressable population. The result is a positive readout for the bispecific antibody modality more broadly.