Claudin 18.2 Results Explained

IHC scoring, gastric cancer and zolbetuximab eligibility

What each line of the report means

Specimen: Tumor tissue, as stated
CLDN18.2 is tested by immunohistochemistry on tumor tissue, not blood.
Biomarker / finding: CLDN18.2 positive
Positivity is defined by the percentage of tumor cells staining at moderate-to-strong intensity, and cutoffs vary by assay and indication.
Scoring: Percent of tumor cells with 2+/3+ membrane staining
The pivotal trials used 75% or more of tumor cells at moderate-to-strong intensity; reports may use a different cutoff.
Clinical interpretation: Cancer-specific review required
A positive result is primarily relevant in advanced gastric and gastroesophageal junction adenocarcinoma; relevance in other cancers is trial-level.

How this result is interpreted

  • CLDN18.2 is a tight-junction protein exposed on the surface of certain gastric and GEJ tumor cells, making it a drug target.
  • A positive result at the trial-defined cutoff can open eligibility for zolbetuximab, an approved CLDN18.2-targeted antibody, in advanced gastric/GEJ adenocarcinoma.
  • Borderline or low-percentage staining should be read against the exact assay and cutoff used - different antibodies and thresholds are not interchangeable.

What this result cannot tell you

  • A negative result applies only to the tested specimen and assay; staining can be heterogeneous between tumor sites.
  • The approved cutoff applies to gastric/GEJ adenocarcinoma; a positive result in another cancer type is a trial-matching lead, not an approved-therapy indication.
  • Older biopsies may not reflect current expression; retesting on progression tissue is sometimes warranted.

Questions to ask your oncologist

  • What exact percentage and staining intensity did my report show, and which antibody clone was used?
  • Does my result meet the cutoff used in the zolbetuximab trials?
  • Were HER2, PD-L1, MMR and CLDN18.2 all tested on my tumor, or are any still pending?
  • If my cancer is not gastric/GEJ, are there CLDN18.2-directed trials I could match?

Frequently asked questions

Does CLDN18.2 positive mean I should get zolbetuximab?

Not automatically. Eligibility depends on the exact staining cutoff, cancer type, prior treatment, and current approvals - the result opens a conversation, it does not close one.

Can a negative CLDN18.2 result be wrong?

Staining can vary between tumor sites and between assays. If the result is central to a treatment decision and the sample was small or old, repeat testing on a different specimen can be reasonable.

Can someone independently review this result?

Yes. A Clarity Report can assess the staining report, assay, cancer type, and current trial and approval landscape, then return findings in writing.

Sources

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