Roche has received expanded U.S. Food and Drug Administration approval for the PATHWAY HER2 (4B5) test and VENTANA HER2 Dual ISH DNA Probe Cocktail, enabling the companion diagnostics to identify HER2-positive metastatic gastroesophageal adenocarcinoma patients who may be eligible for treatment with Jazz Pharmaceuticals plc’s ZIIHERA, or zanidatamab. The tests can now support HER2 assessment across gastric, gastroesophageal-junction and esophageal adenocarcinoma.
The diagnostic approval arrived alongside a major therapeutic expansion for ZIIHERA. The FDA approved zanidatamab with fluoropyrimidine- and platinum-containing chemotherapy plus BeOne Medicines USA, Inc.’s tislelizumab for first-line treatment of adults with HER2-positive unresectable locally advanced or metastatic gastric, gastroesophageal-junction or esophageal adenocarcinoma meeting defined biomarker criteria. The agency also approved a ZIIHERA-plus-chemotherapy regimen for patients with IHC 3+ tumors.
Why are companion diagnostics essential to HER2-targeted cancer treatment?
HER2 is a receptor involved in cell growth and signaling. Some tumors produce excessive HER2 protein because the underlying ERBB2 gene is amplified or otherwise dysregulated, creating a biological vulnerability that can be targeted with HER2-directed medicines.
The challenge is that a drug designed for HER2-positive cancer is not expected to benefit every patient with the same anatomical cancer diagnosis. Pathologists therefore need validated assays that determine whether an individual tumor meets the biomarker criteria associated with the drug’s approved use.
A companion diagnostic makes that relationship explicit. The test is not simply additional information for the oncologist; it becomes part of determining whether a patient is eligible for a particular targeted therapy under the regulatory label.
Roche’s expanded approvals are particularly important in esophageal adenocarcinoma because the company says no test had previously been approved to determine HER2 status in esophageal cancer for this treatment context.
How do the two Roche HER2 tests work differently?
The PATHWAY HER2 (4B5) Rabbit Monoclonal Primary Antibody test uses immunohistochemistry, or IHC, to evaluate the amount and pattern of HER2 protein expressed in tumor tissue. Pathologists assign an IHC score based on the staining characteristics, helping distinguish strongly HER2-positive tumors from negative or equivocal specimens.
Roche says the assay is integrated with its automated VENTANA BenchMark slide-staining platform, reducing manual steps and helping laboratories standardize the immunohistochemical workflow.
The VENTANA HER2 Dual ISH DNA Probe Cocktail addresses the biomarker from another angle. Instead of primarily measuring HER2 protein, the in situ hybridization assay detects amplification of the HER2 gene. Its dual-color design allows pathologists to assess HER2 gene copies in relation to a reference signal directly within the tissue.
These methods can work together when the IHC result is not unequivocal. Under the new ZIIHERA indication, patients with an IHC 3+ result can meet the HER2-positive definition, while some IHC 2+ tumors require confirmation of gene amplification through ISH.
How does the diagnostic determine which ZIIHERA regimen a patient can receive?
The FDA’s therapeutic approval creates an unusually visible example of how biomarker detail can shape not merely whether a patient receives a medicine but which combination regimen is available.
ZIIHERA combined with chemotherapy and tislelizumab is approved for first-line treatment of patients whose tumors are HER2 positive at IHC 3+ or IHC 2+ with ISH confirmation. ZIIHERA plus chemotherapy without tislelizumab is approved for the IHC 3+ population specified in the label.
That structure makes accurate pathology critical. A tumor categorized incorrectly near a threshold could influence the treatment pathway, reinforcing why precision oncology depends as much on reproducible diagnostic assays as on the drug itself.
The broader lesson is that oncology innovation increasingly arrives as a paired system. Pharmaceutical companies may develop the therapy, but diagnostic manufacturers provide the infrastructure required to identify the molecularly defined population in which that therapy was shown to work.
Why is gastroesophageal adenocarcinoma an important diagnostic challenge?
Gastroesophageal adenocarcinoma encompasses related malignancies arising in the stomach, gastroesophageal junction and esophagus. Roche notes that these aggressive cancers are frequently diagnosed at advanced stages, when systemic treatment rather than curative local therapy becomes the primary option.
Biomarker testing becomes particularly important in this setting because treatment choices can depend on HER2 status and other molecular or immune characteristics. The pathology laboratory therefore sits at the beginning of an increasingly complicated treatment-selection pathway.
That complexity is likely to increase as more targeted agents, bispecific antibodies, antibody-drug conjugates and immunotherapy combinations move into gastroesophageal cancers. A tissue specimen may eventually need to support several biomarker decisions rather than a single binary test.
Roche’s strategy reflects that transition. The company operates both a pharmaceutical business and one of the world’s largest diagnostics franchises, allowing biomarker development and therapeutic development to intersect across precision-medicine programs.
Could companion diagnostics become more valuable as oncology drugs become more precise?
Almost certainly. The narrower a drug’s intended biological population becomes, the more valuable accurate patient identification becomes.
This creates an unusual commercial relationship. A highly effective therapy can fail to reach its potential if testing is unavailable, inconsistent or too slow, while a diagnostic test has limited value unless an actionable treatment exists for patients who test positive.
The result is a co-dependent ecosystem involving drug companies, diagnostic manufacturers, pathologists, oncologists and reference laboratories. Regulatory approvals must increasingly synchronize these components so a new drug does not reach the market without a practical mechanism for finding the patients eligible to receive it.
The ZIIHERA expansion illustrates that dynamic clearly. FDA approval of the drug is the headline therapeutic event, but Roche’s diagnostic expansion determines whether laboratories can translate the biomarker requirements on that label into routine clinical decisions.
What should laboratories watch next?
The immediate challenge will be implementation across pathology laboratories treating patients with gastric, gastroesophageal-junction and esophageal cancers. Existing familiarity with Roche HER2 assays in breast and gastric cancer could help laboratories adopt the expanded indication without building an entirely new testing workflow.
The more interesting future question is how HER2 testing evolves as the number of HER2-directed drugs increases. Different therapies may eventually have different thresholds, scoring systems or sensitivity to heterogeneous and lower levels of HER2 expression.
Pathologists could therefore move from answering a relatively simple question about whether a tumor is HER2 positive to providing a more granular biological profile that helps select among several HER2-targeted approaches.
That makes companion diagnostics more than supporting products attached to oncology drugs. They are becoming decision infrastructure for precision medicine, determining which therapeutic innovation reaches which patient and, increasingly, which combination is selected.
