DataM Intelligence’s report analyzes therapy, stage, end-user and regional segments, including pipeline developments, company positioning and country-level trends. Competition will increasingly depend on HER2 testing, treatment sequencing and the expansion of newly approved or clinically advancing regimens across markets.
-- The global HER2-positive gastric cancer market is valued at US$1.31 billion in 2025 and is forecast to reach US$2.05 billion by 2035, at a 4.6% CAGR, according to DataM Intelligence. The treatment landscape is moving beyond a trastuzumab-led approach: antibody-drug conjugates (ADCs), immunotherapy combinations and bispecific HER2 antibodies are creating new treatment choices across disease stages and lines of therapy.
The FDA’s August 2026 approval of zanidatamab-based regimens puts HER2 test results at the center of treatment selection and creates a new competitive challenge for established trastuzumab combinations. In Japan, where gastric cancer burden is high and trastuzumab deruxtecan has moved into second-line treatment, the next question is how quickly emerging first-line regimens can gain local approval and access.
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United States
On August 25, the FDA approved zanidatamab with chemotherapy and tislelizumab for first-line treatment of eligible HER2-positive, unresectable locally advanced or metastatic gastric, gastroesophageal junction (GEJ) or esophageal adenocarcinoma. Eligibility includes IHC 3+ or IHC 2+/ISH-positive disease. Zanidatamab with chemotherapy alone is approved for IHC 3+ tumors. The FDA also approved companion diagnostic tests to identify eligible patients. This makes reliable HER2 testing essential to access and gives pathology labs a more direct role in treatment selection.
Japan
More than 125,000 gastric cancer cases and over 43,000 deaths were recorded in Japan in 2022, according to Daiichi Sankyo’s release on the country’s treatment update. In March 2026, Japan expanded trastuzumab deruxtecan (Enhertu) to second-line treatment for eligible HER2-positive advanced or recurrent gastric cancer, advancing it from its previous third-line position. Japan also participated in the global HERIZON-GEA-01 trial; the Japanese trial registry recorded Ehime Prefecture as a study location and listed the study as no longer recruiting in its October 15 update. U.S. approval does not establish Japanese approval, so local regulatory status remains a separate commercial consideration.
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Recent Developments
- Phase III results strengthened the case for a new first-line HER2 approach. Results from HERIZON-GEA-01, published on May 27, 2026, showed median progression-free survival of 12.4 months for both zanidatamab-based treatment arms, compared with 8.1 months for trastuzumab plus chemotherapy. The arm combining zanidatamab, tislelizumab and chemotherapy reported median overall survival of 26.4 months, versus 19.2 months in the control arm.
- PD-L1-negative patients remained part of the treatment discussion. Data presented at the 2026 American Society of Clinical Oncology meeting reported benefit with zanidatamab, tislelizumab and chemotherapy across PD-L1 subgroups. This may affect how companies plan testing and communicate the role of PD-L1 alongside HER2 in first-line treatment decisions.
- Diarrhea management is an operational consideration. In HERIZON-GEA-01, diarrhea was the most common grade 3 or higher treatment-related adverse event in the zanidatamab-containing arms. The study used anti-diarrheal prophylaxis during the first cycle; most events occurred early. Treatment implementation will therefore depend in part on clear monitoring and early intervention protocols.
- Japan registered a study for tumors expressing both HER2 and CLDN18.2. The ZAP-HETERO phase II study, registered in June 2026, is evaluating zolbetuximab, trastuzumab and CapeOX, with pembrolizumab use guided by PD-L1 expression. The trial reflects a research question specific to biomarker overlap; it is investigational and does not establish an approved treatment.
- Japan approved perioperative durvalumab for gastric cancer. On June 19, 2026, Japan approved durvalumab for pre- and post-operative treatment of gastric cancer. The approval is not specific to HER2-positive disease, but it signals activity in earlier-stage treatment and may influence how companies assess future perioperative opportunities.
- The FDA approved two first-line zanidatamab regimens on August 25. Zanidatamab with tislelizumab and chemotherapy is approved for HER2 IHC 3+ or IHC 2+/ISH-positive disease. Zanidatamab with chemotherapy alone is approved for IHC 3+ disease. The distinction makes the testing threshold central to treatment eligibility.
- The FDA also approved companion diagnostic devices. The PATHWAY anti-HER-2/neu (4B5) antibody and VENTANA HER2 Dual ISH DNA Probe Cocktail were approved to identify patients eligible for the zanidatamab regimens. The decision links treatment access directly to validated testing workflows.
Market Segmentation:
Targeted therapy represented 38.6% of 2025 market revenue, equal to about US$506 million on the report’s US$1.31 billion market base. This segment includes HER2-directed treatment such as trastuzumab and ADCs. First-line bispecific antibody and immunotherapy combinations are now adding competition within this established targeted-treatment pool.
Stage IV disease accounted for 41.2% of 2025 revenue, or about US$540 million on the same base. The segment’s share reflects the use of systemic therapies in advanced disease, including multiple treatment lines. New first-line approvals and second-line ADC access in Japan may reshape how revenue is distributed across regimens and treatment stages.
Company Profiles
Jazz Pharmaceuticals commercializes zanidatamab in the United States and other territories covered by its license. The FDA’s first-line approval gives Jazz a broader role in HER2-positive gastroesophageal adenocarcinoma beyond the drug’s existing biliary-tract-cancer indication. Execution will depend on uptake of the new combination regimen and on access to HER2 testing.
BeOne Medicines supplies tislelizumab (Tevimbra), the PD-1 inhibitor included in the approved triplet regimen. Its collaboration with Jazz on HERIZON-GEA-01 and the trial’s published results position the company as both a treatment partner and a contributor to first-line clinical evidence.
Zymeworks engineered and first developed zanidatamab, then licensed development and commercialization rights to Jazz and BeOne by territory. Its 2025 Form 10-K describes potential tiered royalties and milestone payments tied to the partners’ sales and regulatory progress, giving Zymeworks an ongoing economic interest in the drug’s commercial expansion.
Daiichi Sankyo and AstraZeneca jointly develop and commercialize trastuzumab deruxtecan (Enhertu). In Japan, Daiichi Sankyo commercializes the ADC and expanded its gastric-cancer use to second-line treatment in March 2026. The product remains a central comparator as new first-line combinations enter the market.
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