FDA Approves Zanidatamab Regimens for First-Line HER2+ Gastric Cancer

Clinical Trial Design and Survival Endpoints in HERIZON-GEA-01

The regulatory authorization stems from data evaluated in the HERIZON-GEA-01 trial (NCT05152147), a randomized, three-arm, open-label, active-comparator global study. Patients with unresectable locally advanced or metastatic HER2-positive gastroesophageal adenocarcinoma were allocated across three distinct treatment arms. Arm A evaluated trastuzumab with investigator’s choice of capecitabine and oxaliplatin or fluorouracil and platinum. Arm B investigated zanidatamab-hrii combined with chemotherapy. Arm C evaluated zanidatamab-hrii paired with tislelizumab-jsgr and chemotherapy, according to the U.S. Food and Drug Administration.

According to findings presented at the 2026 American Society of Clinical Oncology Gastrointestinal Cancers Symposium, Arm C achieved statistically significant improvements in both overall survival and progression-free survival compared to Arm A. The median overall survival reached 26.4 months in the zanidatamab and tislelizumab combination arm, versus 19.2 months in the control arm, yielding a hazard ratio of 0.72. Median progression-free survival reached 12.4 months in Arm C compared to 8.1 months in Arm A, according to FDA efficacy data.

Diagnostic Screening and Biomarker Confirmation

Precise patient selection remains a mandatory precursor to administering the newly approved regimen. Simultaneously with the drug application, the FDA cleared the PATHWAY anti-HER-2/neu (4B5) Rabbit Monoclonal Primary Antibody along with the VENTANA HER2 Dual ISH DNA Probe Cocktail, a pair of companion diagnostic instruments manufactured by Ventana Medical Systems, Inc./Roche Diagnostics. These assays identify patients with HER2-positive status defined as IHC 3+ or IHC 2+/ISH+ across gastric, gastroesophageal junction, and esophageal adenocarcinoma.

Exploratory analyses from the trial highlighted distinct therapeutic responses stratified by baseline expression levels. In patients with HER2 IHC 3+ tumors, Arm B demonstrated a median progression-free survival of 14.2 months, compared to 7.6 months for the control arm.

Dosage Specifications and Safety Profile

The approved labeling outlines specific weight-based dosing for zanidatamab-hrii. Patients under 70 kg should be given a suggested regimen of 1,800 mg once every three weeks or 1,200 mg once every two weeks. For individuals weighing 70 kg or greater, the dose is 2,400 mg every three weeks or 1,600 mg every two weeks, according to the FDA. Tislelizumab is administered at 150 mg every two weeks, 200 mg every three weeks, 300 mg every four weeks, or 400 mg every six weeks until disease progression or unacceptable toxicity.

The prescribing information for zanidatamab-hrii carries a boxed warning for diarrhea and embryo-fetal toxicity, alongside warnings for left ventricular dysfunction and infusion-related reactions. Patients receiving tislelizumab-jsgr face specific cautions regarding embryo-fetal toxicity, infusion reactions, immune-related adverse events, and issues stemming from allogeneic hematopoietic stem cell transplantation.

*Disclaimer: The information provided in this article is for educational and scientific communication purposes only and does not constitute medical advice. Always consult with a qualified healthcare provider regarding any medical condition, diagnosis, or treatment plan.*