Overview

Claudin 18.2 (CLDN18.2) is a tight-junction protein that is aberrantly expressed on the surface of many gastric and gastroesophageal adenocarcinoma cells. Immunohistochemistry (IHC) is used to detect this protein in tumor tissue, providing a biomarker that helps select patients who may be eligible for CLDN18.2-directed therapy. The test turns a generic adenocarcinoma diagnosis into a more stratified decision.

Which Patients Are Considered for CLDN18.2 Assessment

Testing is generally relevant for patients with advanced gastric or gastroesophageal junction adenocarcinoma, where biomarker-driven treatment planning is part of current practice. Not every gastric cancer expresses CLDN18.2, so routine assessment helps avoid offering a targeted option to patients unlikely to benefit.

Patient selection should follow the treating team's protocol and the approved indications in the specific market. The assay is performed on tumor tissue, usually from a biopsy or surgical specimen already obtained for diagnosis.

How IHC Scoring Guides Eligibility

A pathologist evaluates the stained slide for membranous staining on tumor cells. Eligibility is defined by a predefined cutoff of tumor cells showing moderate-to-strong staining, established by the assay and the relevant clinical studies. Consistent scoring depends on validated antibodies and centralized or well-trained reading.

Because scoring is subjective at the edges, laboratories follow standard operating procedures and, where appropriate, peer review of equivocal cases. This discipline protects the reliability of patient selection.

Integration Into the Treatment Pathway

CLDN18.2 testing is typically ordered before a targeted therapy decision, so the result is available alongside other biomarker and imaging data. It complements, rather than replaces, broader staging and performance-status assessment.

For procurement teams, the relevant product is the assay service and its report quality. A clear, standardized report helps oncology teams act quickly and consistently across a patient population. Procurement teams should also confirm that the assay is performed in a laboratory qualified for immunohistochemistry, since staining quality directly affects how reliably the result can guide therapy.

FAQ

Q: What is CLDN18.2? A: It is a claudin family protein abnormally expressed on many gastric cancer cells and used as a treatment-target biomarker.

Q: Which patients receive the test? A: Patients with gastric or gastroesophageal adenocarcinoma being evaluated for biomarker-guided therapy, per local guidelines.

Q: What sample is needed? A: Archived or fresh tumor tissue from a biopsy or surgical specimen is examined by IHC.

Q: Does a positive result guarantee treatment? A: No, it informs eligibility alongside staging, performance status, and the approved indications in the patient's region.