The US Food and Drug Administration cleared two zanidatamab regimens on 25 August 2026. The zanidatamab approval covers first-line treatment of HER2-positive advanced gastro-oesophageal adenocarcinoma. It displaces trastuzumab from a first-line backbone that has anchored the setting since 2010. For Jazz Pharmaceuticals, the decision converts a niche biliary tract product into a potential blockbuster. For British and European payers, it starts a familiar waiting game.
What the zanidatamab approval covers
Regulators cleared two distinct regimens under a single label. The first pairs Ziihera with tislelizumab-jsgr and fluoropyrimidine and platinum containing chemotherapy. That combination applies to tumours scored IHC 3+ or IHC 2+/ISH+. The second regimen drops the checkpoint inhibitor. It treats IHC 3+ disease only.
The indication spans cancers of the stomach, gastro-oesophageal junction and oesophagus. Jazz markets zanidatamab as Ziihera. BeOne Medicines markets tislelizumab as Tevimbra. The scope of the zanidatamab approval is unusually broad for a HER2 targeted agent. Crucially, eligibility does not depend on PD-L1 expression.
Rob Iannone is Executive Vice President and Global Head of Research and Development at Jazz. He is also the company’s Chief Medical Officer. In the company’s announcement he called the outcome a major step forward for patients. He described Ziihera as “the first and only bispecific HER2-targeted antibody combined with a PD-1 inhibitor and chemotherapy”. He said the regimen was cleared “for all HER2+ advanced GEA patients, regardless of PD-L1 status”.
The label also preserves the earlier accelerated approval in biliary tract cancer. Zanidatamab remains a single agent option there after prior systemic therapy. The 25 August action date had been listed among the FDA drug approval decisions tracked by this publication for August.
Inside the HERIZON-GEA-01 evidence
The zanidatamab approval rests on HERIZON-GEA-01, a global phase 3 trial registered as NCT05152147. Investigators randomised 914 patients across roughly 225 sites in more than 30 countries. Randomisation ran one to one to one across three arms.
The control arm received trastuzumab plus chemotherapy. The second arm received zanidatamab plus chemotherapy. The third arm added tislelizumab to that backbone. Progression-free survival and overall survival served as dual primary endpoints. Blinded independent central review assessed progression-free survival, using RECIST version 1.1.
Results appeared in the New England Journal of Medicine on 27 May 2026.
Survival and progression endpoints
Median overall survival reached 26.4 months in the triplet arm. The trastuzumab comparator recorded 19.2 months. The hazard ratio was 0.72, with a 95 per cent confidence interval of 0.57 to 0.90. The p value was 0.0043.
Median progression-free survival reached 12.4 months against 8.1 months. That produced a hazard ratio of 0.63, with a confidence interval of 0.51 to 0.78. The p value fell below 0.0001. Both figures come from the same interim analysis timepoint reported by the FDA.
The chemotherapy doublet arm recorded a median overall survival of 24.4 months, with a hazard ratio of 0.80. That result did not meet the prespecified threshold for statistical significance at the first interim analysis. Zymeworks has said top-line results from a second interim analysis of the doublet arm were expected in the third quarter of 2026.
Geoffrey Ku, Associate Attending Physician in the Gastrointestinal Oncology Service at Memorial Sloan Kettering Cancer Center, co-authored the study. He discloses financial interests related to Jazz Pharmaceuticals. In the company’s announcement he observed that “similar outcomes were seen in patients whose tumors were PD-L1 positive or PD-L1 negative”. He added that the regimen could therefore benefit a broad range of patients.
Safety and the boxed warning
The label carries a boxed warning. It states that the regimen “can cause severe diarrhea, including life threatening and fatal cases”. A second boxed element covers embryo-fetal harm during pregnancy.
In HERIZON-GEA-01, diarrhoea affected 83 per cent of patients on the triplet regimen. The chemotherapy doublet without tislelizumab produced diarrhoea in 79 per cent. Nausea, vomiting and decreased appetite each reached 40 per cent or more in both arms. Warnings and precautions also cover left ventricular dysfunction and infusion-related reactions.
Prescribers therefore inherit a demanding toxicity conversation. Supportive care protocols will shape real-world persistence on therapy. The label reports permanent discontinuation of Ziihera for left ventricular dysfunction in 3 per cent of patients on the triplet regimen. The figure was 1.0 per cent on the doublet.
Pressure on a 15-year trastuzumab standard
Trastuzumab plus chemotherapy has defined this setting since the ToGA trial reported in 2010. That study established routine HER2 testing in advanced gastric and gastro-oesophageal junction cancer. No regimen had displaced trastuzumab itself from the first-line backbone until now.
Roche’s HER2 franchise already faces biosimilar erosion in Europe and North America. The zanidatamab approval adds direct clinical displacement to that pricing pressure, although the company retains a position in the diagnostic pathway. Guideline committees will now revisit first-line treatment algorithms.
How it sits against the pembrolizumab regimen
Merck’s Keytruda already holds a first-line HER2-positive gastric indication. The FDA approved that regimen in March 2025, converting an accelerated approval first granted in May 2021. It combines pembrolizumab with trastuzumab and chemotherapy. Critically, the label restricts use to tumours expressing PD-L1 at a combined positive score of one or above.
KEYNOTE-811 reported median overall survival of 20.1 months against 15.7 months. The hazard ratio was 0.79, with a 95 per cent confidence interval of 0.66 to 0.95. Those figures come from that trial’s own analysis timepoint.
The two datasets are not directly comparable. Populations, control arms and analysis timepoints all differ. HERIZON-GEA-01 compared its arms against trastuzumab plus chemotherapy. KEYNOTE-811 compared against trastuzumab, chemotherapy and placebo. No head-to-head trial exists.
The label difference is nonetheless commercially decisive. Merck’s regimen serves only PD-L1 positive patients. Jazz’s triplet serves the whole HER2-positive population.
Consequences for diagnostic pathways
Diagnostic laboratories face a second consequence. The triplet regimen covers IHC 2+/ISH+ tumours as well as IHC 3+ disease. Reflex in situ hybridisation testing therefore gains commercial weight. Pathology services that batch or defer ISH may need to revise turnaround targets.
The FDA approved two Roche companion diagnostics alongside the drug. Both come from Ventana Medical Systems: the PATHWAY anti-HER-2/neu (4B5) antibody and the VENTANA HER2 Dual ISH DNA Probe Cocktail. Roche therefore loses first-line therapeutic share while gaining the assays that gate access to the new regimen.
Around 20 per cent of gastro-oesophageal adenocarcinoma cases test HER2-positive, according to BeOne Medicines. The company also cited more than 31,000 new US stomach cancer diagnoses each year. Fewer than 40 per cent of US patients with advanced HER2-positive disease survive beyond two years.
Commercial stakes for Jazz, Zymeworks and BeOne
Zymeworks discovered and engineered zanidatamab using its Azymetric bispecific platform. The company disclosed a $250 million milestone triggered by the zanidatamab approval. Its regulatory filing flags up to $1.3 billion in further milestones from Jazz.
Zymeworks also remains eligible for up to $144 million tied to the BeOne collaboration. Royalties run at tiered rates of up to 20 per cent across Jazz territories. Rates reach up to 19.5 per cent in BeOne territories. This is the second FDA approval for zanidatamab in less than two years.
Analyst expectations diverge sharply. RBC Capital Markets has pointed to a market opportunity above $1.5 billion. Stifel has modelled $650 million to $700 million in US gastro-oesophageal sales. Roughly 12,000 US patients now qualify, against about 1,500 in biliary tract cancer.
Both banks also flagged the breadth of the label. The FDA cleared use in tumours with lower HER2 expression, and in oesophageal and junctional tumours. The trial population was weighted towards gastric cancer and IHC 3+ disease. The regulator’s own review supports the concern. Exploratory analysis attributed the doublet arm’s benefit primarily to the IHC 3+ subgroup. That is why the regimen is restricted to IHC 3+ tumours.
Mark Lanasa, Chief Medical Officer for Solid Tumours at BeOne Medicines, welcomed the clearance in the company’s announcement. He called it an important milestone for BeOne, describing Tevimbra as the first approved foundational asset to emerge from its solid tumour portfolio. Jaffer A. Ajani, Professor of Gastrointestinal Medical Oncology at the University of Texas MD Anderson Cancer Center, framed the survival result plainly in the same announcement. He said outcomes in this setting had “historically been challenging to improve”.
The UK and European access gap
British and European prescribers cannot yet use the regimen. The zanidatamab approval applies only in the United States. The MHRA granted Ziihera a Great Britain licence for biliary tract cancer on 19 February 2026, through the International Recognition Procedure. The European Commission granted a conditional marketing authorisation for the same indication in July 2025.
NICE recommended zanidatamab for advanced biliary tract cancer in final draft guidance in April 2026, publishing final guidance as TA1153 on 7 May 2026. That decision routed the drug through routine commissioning rather than the Cancer Drugs Fund. It followed a draft rejection in January, later reversed after further evidence.
The gastro-oesophageal indication must repeat that journey. Around 6,800 people receive a stomach cancer diagnosis in the UK each year, according to Cancer Research UK. Oesophageal cancer adds a considerably larger annual burden.
A regulatory review is already under way. The FDA conducted its assessment under Project Orbis, its framework for concurrent international review. The agency worked with the MHRA and Health Canada. The agency states that the application reviews remain ongoing at both. Jazz has not disclosed a filing date for the European Union. It says only that it continues to pursue additional approvals worldwide. NHS commissioners therefore have a live MHRA process to plan against. They have no published decision timetable, and no NICE appraisal yet under way for this indication. Trusts running HER2 testing pathways should expect demand to build.
What the sector should watch next
Four questions now dominate the commercial picture. First, how quickly the MHRA and Health Canada conclude their Project Orbis reviews. Second, when Jazz files in the European Union and Japan. Third, whether payers accept a triplet regimen carrying substantial diarrhoea rates. Fourth, how zanidatamab performs against antibody drug conjugates in later treatment lines.
Jazz is also testing zanidatamab in breast cancer. Readouts there could arrive in late 2027. The HERIZON-GEA-301 confirmatory trial in gastro-oesophageal adenocarcinoma remains ongoing. A positive result would broaden the franchise well beyond gastrointestinal tumours. It would also intensify competition with established HER2 agents.
For now, the zanidatamab approval marks the first change to the first-line HER2-positive gastro-oesophageal backbone in 15 years. Jazz describes it as a new standard of care. British oncologists and commissioners will watch the regulatory queue closely.
