Jazz Pharmaceuticals has reported a second positive overall survival result for Ziihera (zanidatamab-hrii) in a Phase 3 study of patients with HER2-positive advanced gastroesophageal adenocarcinoma. The latest results show that Ziihera combined with chemotherapy significantly improved overall survival compared with the established trastuzumab-based regimen, adding to the drug’s recent FDA approval in the first-line treatment setting.
- Ziihera plus chemotherapy delivered a statistically significant overall survival benefit compared with trastuzumab plus chemotherapy.
- The result came from the second interim analysis of the Phase 3 HERIZON-GEA-01 trial.
- A separate Ziihera regimen combining the drug with Tevimbra and chemotherapy had already demonstrated a significant survival benefit.
- The FDA approved Ziihera-based regimens for first-line HER2-positive advanced gastroesophageal adenocarcinoma on August 25, 2026.
- Jazz has raised its projected peak sales range for Ziihera to $3 billion-$5 billion.
- The company is positioning the drug as a new HER2-targeted treatment option for advanced stomach, gastroesophageal junction and esophageal cancers.
Second Overall Survival Result From HERIZON-GEA-01
The latest data come from the ongoing HERIZON-GEA-01 Phase 3 trial, which is evaluating Ziihera-containing treatment regimens against trastuzumab plus chemotherapy in patients with previously untreated HER2-positive advanced gastroesophageal adenocarcinoma.
At the second interim analysis, the combination of Ziihera and chemotherapy achieved a statistically significant and clinically meaningful improvement in overall survival compared with trastuzumab and chemotherapy.
The result is particularly significant because the same Ziihera-plus-chemotherapy regimen had not reached statistical significance for overall survival at the first interim analysis. At that earlier point, the treatment had shown a favorable trend toward reducing the risk of death, but the difference did not meet the prespecified threshold for statistical significance.
Jazz said the updated analysis showed an improvement in the magnitude of benefit for both Ziihera treatment combinations evaluated in the trial.
Ziihera Previously Demonstrated Benefit With Tevimbra
The latest result follows an earlier positive survival outcome for a three-drug regimen combining Ziihera, Tevimbra (tislelizumab) and chemotherapy.
At the first interim analysis, that combination reduced the risk of death by 28% compared with trastuzumab plus chemotherapy. Median overall survival was 26.4 months, compared with 19.2 months for the control group.
With longer follow-up, Jazz said the overall survival hazard ratio for the Tevimbra-containing regimen has improved further, strengthening the company’s case for Ziihera-based treatment in the first-line setting. Updated data are expected to be presented at a medical meeting in the fourth quarter of 2026.
The trial is therefore providing survival data for two different Ziihera-based approaches: one pairing Ziihera with chemotherapy alone and another adding the PD-1 inhibitor Tevimbra.
FDA Recently Expanded Ziihera’s Use
The new trial results arrive less than a week after the FDA expanded Ziihera’s approved uses.
On August 25, the agency approved Ziihera in combination with fluoropyrimidine- and platinum-based chemotherapy plus Tevimbra for adults with unresectable, locally advanced or metastatic HER2-positive gastric, gastroesophageal junction or esophageal adenocarcinoma.
The approval covers patients whose tumors are classified as HER2 IHC 3+ or IHC 2+/ISH+, regardless of PD-L1 status.
The FDA also approved Ziihera with chemotherapy alone for patients with HER2 IHC 3+ tumors in the same first-line setting.
Trastuzumab Has Been the Established Standard
The development is significant because trastuzumab, marketed as Herceptin, has been a longstanding component of first-line treatment for HER2-positive advanced gastroesophageal cancer.
The HERIZON-GEA-01 trial directly compared Ziihera-based regimens with trastuzumab and chemotherapy, providing a head-to-head assessment of the two HER2-targeted approaches.
The first-line approval and latest survival data give Jazz a clinical basis for challenging the established treatment approach in HER2-positive advanced gastroesophageal adenocarcinoma.
Ziihera Targets HER2 Through a Bispecific Design
Ziihera is a bispecific antibody designed to bind two different extracellular regions of the HER2 receptor.
By attaching to separate HER2 receptors, the drug can bring those receptors together and promote receptor clustering. This mechanism is intended to interfere with HER2 signaling while also promoting immune-mediated destruction of cancer cells.
The drug’s ability to combine HER2 targeting with immune activity is particularly relevant to the regimen containing Tevimbra, which blocks the PD-1 immune checkpoint.
The latest results add further confidence to the treatment strategy in patients with advanced HER2-positive gastroesophageal cancers. Overall survival is especially important in this setting because many patients are diagnosed after the disease has already become difficult to treat with surgery alone.
Importance of First-Line Treatment
First-line therapy plays a critical role because it establishes the initial treatment approach after diagnosis of unresectable or metastatic disease. Improving outcomes at this stage can give patients more time before the disease progresses and may create additional opportunities for subsequent treatments.
Advances in HER2-Directed Therapy
The findings reflect broader progress in targeted cancer treatment. Researchers are increasingly developing therapies that interact with tumor proteins in more sophisticated ways, while combination approaches aim to attack cancer through complementary mechanisms.
Implications for Oncologists
The new evidence may provide oncologists with additional information when considering treatment options for eligible patients. Decisions will continue to depend on factors such as HER2 status, disease extent, previous treatment, overall health, tolerability, and patient preferences.
Continued Clinical Development
Long-term follow-up will remain important for understanding how durable the survival advantage is. Researchers will also continue evaluating treatment combinations, safety outcomes, and whether similar strategies can benefit additional patient populations.
Importance of HER2 Testing
HER2 testing helps identify patients who may benefit from HER2-directed treatment. Accurate testing is essential because HER2 expression can vary between tumors, and treatment eligibility depends on confirmed laboratory results. Pathologists may use immunohistochemistry and additional testing methods to determine HER2 status.
Combination Therapy in Advanced Disease
Combining targeted treatment with chemotherapy or immunotherapy may improve disease control by attacking cancer through different mechanisms. Chemotherapy can damage rapidly dividing cells, while targeted antibodies focus on specific proteins involved in tumor growth. Immunotherapy may also help the immune system recognize and attack cancer cells.
Survival as a Key Clinical Endpoint
Overall survival remains one of the most important measures in advanced cancer trials. Progression-free survival can show how long treatment delays disease worsening, but overall survival provides a clearer picture of whether patients live longer. Researchers also assess response rates, duration of response, quality of life, and treatment tolerability.
Managing Treatment Side Effects
Patients receiving combination regimens may experience gastrointestinal symptoms, fatigue, reduced appetite, infusion-related reactions, or changes in blood counts. Supportive care, dose adjustments, monitoring, and early symptom management can help patients continue treatment safely.
Future Directions in Stomach Cancer Care
Future research will likely focus on identifying which patients benefit most from specific combinations. Biomarker testing, molecular profiling, and real-world evidence may help physicians personalize treatment decisions. Additional studies will also clarify how targeted therapies should be used after disease progression or alongside other emerging treatments.
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