CLDN 18.2

Reporting test results

Review best practices for accurate and consistent reporting of CLDN18.2 expression and positivity.

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Accurate reporting of CLDN18.2 expression requires assessment of both membranous staining intensity and the percentage of tumor cells stained1

In addition to membranous stain intensity and percentage of tumor cells stained, it is recommended that the biomarker report also include:

  • Type of testing method and antibody used, including companion diagnostic vs laboratory-developed test, antibody clone, and IHC stainer used
  • A description of the status of the sample, such as “positive,” “negative,” or “inconclusive,” including how positivity was defined
  • Type of specimen (biopsy vs surgical) and site of the sampling (primary vs metastatic disease; if metastatic, define the site)
  • Sample adequacy; if inadequate, state the cause
  • Any relevant notes or observations regarding the sample or
    results

How to Report CLDN18.2

Kristina A. Matkowskyj, MD, PhD

The current standard for CLDN18.2-positivity, based on IHC assessment in two recently published global Phase 3 studies, is ≥75% of tumor cells demonstrating moderate-to-strong (2+/3+) membranous CLDN18 staining.2,3

CLDN18.2 reporting template

Developed by a committee of experts, consider the following example template when integrating CLDN18.2 reporting into your current protocols.

Using the CLDN18.2 Reporting Template

Kristina A. Matkowskyj, MD, PhD

Consistent, integrated reporting of biomarkers can inform clinical decision-making and may improve patient care4

Integrated biomarker reporting

  • Helps inform the multidisciplinary team’s clinical approach based on biomarker test results
  • Can be used as a tool to help pathologists educate the multidisciplinary team

Pathologists drive consistent, integrated reporting, helping their multidisciplinary teams optimize treatment plans.

Gain more in-depth knowledge on our resources page

CLDN18, claudin 18; CLDN18.2, claudin 18 isoform 2; IHC, immunohistochemistry.

References:

  • 1. Fassan M, Kuwata T, Matkowskyj KA, et al. Claudin-18.2 immunohistochemical evaluation in gastric and gastroesophageal junction adenocarcinomas to direct targeted therapy: a practical approach. Mod Pathol. 2024;37(11):100589.
  • 2. Shitara K, Xu RH, Ajani JA, et al. Global prevalence of claudin 18 isoform 2 in tumours of patients with locally advanced unresectable or metastatic gastric or gastroesophageal junction adenocarcinoma. Gastric Cancer. 2024;27(5):1058-1068.
  • 3. Shah MA, Shitara K, Ajani JA, et al. Nat Med. 2023;29(8):2133-2141.
  • 4. Warner JL, Jain SK, Levy MA. Integrating cancer genomic data into electronic health records [published online October 26, 2016]. Genome Med. 2016. Accessed June 19, 2026. https://genomemedicine.biomedcentral.com/articles/10.1186/s13073-016-0371-3