FDA Approves New Ziihera-Based Treatment Regimens for HER2-Positive Gastroesophageal Cancer

The U.S. Food and Drug Administration (FDA) has approved two Ziihera (zanidatamab-hrii)-containing treatment regimens for the first-line treatment of adults with unresectable, locally advanced or metastatic HER2-positive gastroesophageal adenocarcinoma (GEA). The announcement was made by Jazz Pharmaceuticals on August 25, 2026.

The approval introduces new options for patients whose tumors express HER2, a protein that can contribute to cancer growth. GEA includes cancers affecting the stomach, gastroesophageal junction and esophagus. According to the source, approximately 20% of patients with GEA have HER2-positive disease, highlighting the importance of identifying HER2 status when planning treatment.

What Has Been Approved?

The FDA approval covers two Ziihera-based combinations. The first combines Ziihera with tislelizumab-jsgr (Tevimbra) and fluoropyrimidine- and platinum-containing chemotherapy for patients with HER2-positive disease classified as IHC 3+ or IHC 2+/ISH+. The second combines Ziihera with fluoropyrimidine- and platinum-containing chemotherapy for patients with HER2-positive disease classified as IHC 3+. The relevant HER2 status must be determined using an FDA-authorized test.

This distinction is important because HER2 testing helps determine whether a patient may be eligible for a HER2-directed treatment strategy. The approval therefore adds another option to the treatment landscape for advanced HER2-positive GEA.

Results From the HERIZON-GEA-01 Trial

The FDA decision was based on results from the Phase 3 HERIZON-GEA-01 clinical trial. The study results were published in the New England Journal of Medicine and presented at oncology conferences, with additional analyses planned because the trial remains ongoing.

One of the most notable findings involved progression-free survival (PFS). The Ziihera-containing regimens improved PFS in the overall HER2-positive population, with a reported 35% reduction in the risk of disease progression or death. Median PFS increased to 12.4 months compared with 8.1 months for trastuzumab plus chemotherapy.

Overall survival (OS) was another important outcome. For patients receiving Ziihera with tislelizumab-jsgr and chemotherapy, the reported median OS was 26.4 months compared with 19.2 months for trastuzumab plus chemotherapy. This represented a statistically significant and clinically meaningful reduction in the risk of death of 28%, according to the company announcement.

The reported benefits were generally consistent across major prespecified subgroups, including geographic region and PD-L1 status. This finding is particularly relevant because it suggests that treatment outcomes were not limited to a narrowly defined PD-L1 population.

Why HER2 Testing Matters

HER2 testing has an important role in treatment planning for advanced or metastatic gastroesophageal adenocarcinoma. Tumors can differ significantly in their molecular characteristics, and identifying HER2-positive disease can help clinicians determine whether HER2-directed therapy is appropriate.

The source emphasizes that HER2 testing at diagnosis of advanced or metastatic GEA is critical for guiding treatment selection. The new FDA approval further highlights the role of biomarker testing in matching patients with therapies designed around specific characteristics of their cancer.

How Ziihera Works

Ziihera, also known as zanidatamab-hrii, is a bispecific antibody directed against HER2. According to the prescribing information summarized in the source, the medicine binds to two extracellular sites on HER2. This interaction can promote internalization and reduce HER2 expression on the surface of tumor cells.

The medicine is also associated with immune-related mechanisms, including complement-dependent cytotoxicity, antibody-dependent cellular cytotoxicity and antibody-dependent cellular phagocytosis. These mechanisms contribute to inhibition of tumor growth and cancer-cell death in laboratory and animal studies.

Safety Considerations

While the new approval represents an important treatment development, Ziihera also carries significant safety warnings. The U.S. prescribing information contains boxed warnings for severe diarrhea and embryo-fetal toxicity.

Diarrhea was the most frequently reported adverse reaction in the clinical studies. When Ziihera was combined with chemotherapy and tislelizumab-jsgr, diarrhea was reported in 85% of patients in the cited clinical-study population. Grade 3 and Grade 4 cases occurred, and the source reports that fatal outcomes related to diarrhea occurred in 1.5% of patients.

Because of this risk, loperamide prophylaxis is recommended during the first treatment cycle when Ziihera is administered with the specified chemotherapy combinations, with additional antidiarrheal treatment, fluids and electrolyte replacement used when clinically appropriate. Treatment may need to be interrupted, reduced or discontinued depending on severity.

Other important safety considerations include possible decreases in left ventricular ejection fraction, infusion-related reactions and embryo-fetal toxicity. Patients receiving treatment require appropriate monitoring and medical management based on their individual circumstances.

What This Means for Patients

For adults with advanced HER2-positive GEA, the approval provides additional first-line treatment options. The combination involving Ziihera, tislelizumab-jsgr and chemotherapy is approved for a broader HER2-positive population, including IHC 3+ and IHC 2+/ISH+ disease, regardless of PD-L1 status according to the announcement.

However, treatment decisions remain individual. Factors such as HER2 testing results, overall health, cancer characteristics, previous treatments and potential risks need to be considered by a qualified oncology team.

The approval also reinforces the growing importance of precision medicine in gastroesophageal cancer. Rather than relying exclusively on traditional classifications, modern treatment increasingly incorporates biomarkers such as HER2 to identify patients who may benefit from targeted therapies.

Conclusion

The FDA approval of Ziihera-based first-line regimens marks a significant development for adults with advanced HER2-positive gastroesophageal adenocarcinoma. Results from HERIZON-GEA-01 demonstrated improvements in progression-free and overall survival compared with trastuzumab plus chemotherapy, while subgroup findings indicated generally consistent benefits across geographic and PD-L1 categories.

At the same time, the treatment carries important risks, particularly severe diarrhea, embryo-fetal toxicity, cardiac effects and infusion-related reactions. Patients and healthcare professionals should carefully review the full prescribing information before treatment.

Disclaimer: This article is for general educational and informational purposes only. It is not medical advice, does not replace consultation with a qualified healthcare professional and should not be used to diagnose, treat or prevent any medical condition. Treatment decisions should be made with an appropriate oncology team based on an individual patient's medical history, test results and clinical circumstances.

Source: Jazz Pharmaceuticals, U.S. FDA Approves Ziihera (zanidatamab-hrii) with and without Tislelizumab plus Chemotherapy in First-Line HER2+ Advanced Gastroesophageal Adenocarcinoma, August 25, 2026.