September 03, 2026 – Dublin -- Jazz Pharmaceuticals plc (Nasdaq: JAZZ) reported that Ziihera (zanidatamab-hrii) combined with chemotherapy produced a statistically significant and clinically meaningful overall survival (OS) benefit versus trastuzumab plus chemotherapy in a second interim analysis of the Phase 3 HERIZON-GEA-01 trial in first-line HER2-positive gastroesophageal adenocarcinoma (GEA).
OS hazard ratio for Ziihera plus chemotherapy improved versus the first interim analysis
The company said the survival advantage strengthened compared with earlier data, reinforcing Ziihera's position following its FDA approval on August 25, 2026. No new safety signals emerged relative to previously reported HERIZON-GEA-01 data or the known profiles of the individual agents.
Longer follow-up shows improved OS hazard ratio for the tislelizumab triplet regimen
With extended follow-up, the combination of Ziihera plus Tevimbra (tislelizumab-jsgr) and chemotherapy also showed an improved OS hazard ratio versus the first interim analysis, building on results previously published in The New England Journal of Medicine.
"These HERIZON-GEA-01 results show that Ziihera-based regimens extend OS, demonstrating definitive superiority of Ziihera over trastuzumab and setting a new benchmark for what a first-line HER2-targeted therapy can achieve," said Dr. Kohei Shitara, director of the Department of Gastrointestinal Oncology at the National Cancer Center Hospital East, Kashiwa, Japan, and principal trial investigator.
Trial enrolled 914 patients across roughly 225 sites in more than 30 countries
HERIZON-GEA-01, conducted jointly with BeOne Medicines, randomized patients into three arms: zanidatamab plus chemotherapy and tislelizumab, zanidatamab plus chemotherapy alone, and trastuzumab plus chemotherapy, evaluating dual primary endpoints of PFS by blinded independent central review and OS.
FDA approval covers two Ziihera regimens for HER2-positive GEA
The August 25 approval authorizes Ziihera in combination with tislelizumab and chemotherapy for HER2+ (IHC 3+ and IHC 2+/ISH+) unresectable locally advanced or metastatic GEA, and Ziihera plus chemotherapy alone for HER2+ (IHC 3+) disease. Jazz executive Rob Iannone said the company is moving to establish the tislelizumab-based triplet as the new U.S. standard of care.
Diarrhea occurred in up to 85% of patients on the triplet regimen
Ziihera carries boxed warnings for diarrhea and embryo-fetal toxicity. In the triplet arm, diarrhea occurred in 85% of 330 patients, including Grade 3 (24%) and Grade 4 (2.1%) events, with fatal outcomes in 1.5% of patients; permanent discontinuation due to diarrhea occurred in 3.9%. In the chemotherapy-only arm, diarrhea occurred in 81% of 395 patients, with permanent discontinuation in 1.8%.
Data slated for presentation at a major medical meeting in the fourth quarter of 2026
Jazz has submitted the interim results for conference presentation and plans further submissions to global health authorities, with GEA representing roughly 20% HER2-positive prevalence among a cancer type ranking fifth most common worldwide and a global five-year survival rate below 10% for metastatic disease.