September 03, 2026 – Dublin -- Jazz Pharmaceuticals plc (Nasdaq: JAZZ) reported that Ziihera (zanidatamab-hrii) plus chemotherapy achieved a statistically significant and clinically meaningful overall survival benefit over trastuzumab plus chemotherapy in first-line treatment of HER2-positive advanced gastroesophageal adenocarcinoma (GEA), based on a second interim analysis of the Phase 3 HERIZON-GEA-01 trial.
Ziihera's survival hazard ratio improved from the first interim analysis
The Ziihera plus chemotherapy arm showed an improved OS hazard ratio compared with the trial's first interim readout, according to Jazz. The company said the safety profile remained consistent with prior HERIZON-GEA-01 data and each agent's known profile, with no new safety signals identified.
Tislelizumab combination also strengthens with longer follow-up
With extended follow-up, the Ziihera plus Tevimbra (tislelizumab-jsgr) and chemotherapy regimen also showed an improved OS hazard ratio versus the first interim analysis, building on results previously published in The New England Journal of Medicine. Jazz said this triplet regimen demonstrated durable, statistically significant OS improvement.
FDA approval on August 25 preceded the updated data
The FDA approved Ziihera in combination with tislelizumab and chemotherapy for first-line treatment of adults with HER2+ (IHC 3+ and IHC 2+/ISH+) unresectable, locally advanced or metastatic GEA, and Ziihera plus chemotherapy alone for HER2+ (IHC 3+) disease, on August 25, 2026. Rob Iannone, chief medical officer of Jazz Pharmaceuticals, said the updated results reinforce Ziihera plus tislelizumab and chemotherapy as the new U.S. standard of care, replacing trastuzumab as the HER2-targeted backbone therapy.
Trial enrolled 914 patients across more than 30 countries
HERIZON-GEA-01, conducted jointly with BeOne Medicines, randomized 914 patients at approximately 225 sites in over 30 countries into three arms: zanidatamab plus chemotherapy and tislelizumab; zanidatamab plus chemotherapy; and trastuzumab plus chemotherapy. The trial's dual primary endpoints were progression-free survival by blinded independent central review and overall survival.
Data submission targets a major medical meeting in Q4 2026
Jazz said it has submitted the interim OS data for presentation at a major medical meeting in the fourth quarter of 2026 and will submit the results to global health authorities. Dr. Kohei Shitara, principal trial investigator at the National Cancer Center Hospital East in Kashiwa, Japan, said the results demonstrate definitive OS superiority of Ziihera over trastuzumab, which has anchored first-line GEA treatment for years.
GEA carries poor prognosis with limited treatment history
GEA, encompassing cancers of the stomach, gastroesophageal junction and esophagus, ranks as the fifth most common cancer worldwide, with roughly 20% of patients presenting HER2+ disease. Global five-year survival for metastatic GEA remains below 10%. Ziihera's U.S. label carries Boxed Warnings for diarrhea and embryo-fetal toxicity.