What is the prevalence of CLDN18.2 expression in gastric adenocarcinoma patients?
CLDN18.2 (claudin 18 isoform 2) is a protein found on the surface of many gastric cancer cells. It matters because it is now a drug target: the medicine zolbetuximab is approved for patients whose tumors test positive for it 46. The prevalence, meaning how common it is, depends heavily on how you define positive. When researchers use the strict cutoff from the major clinical trials (at least 75% of tumor cells showing moderate-to-strong staining), the pooled rate is about 34% 4. A separate Western study using a clinical cutoff found about 30% 6. Older studies using looser cutoffs report much higher numbers, up to 87% 8.
What the research says
A 2026 systematic review and meta-analysis pooled data from studies that used the same threshold as the pivotal phase III trials (at least 75% moderate-to-strong membranous staining). It found a pooled CLDN18.2 prevalence of 33.99% in gastric and gastroesophageal junction adenocarcinoma 4. The authors noted that reported estimates vary widely because of differences in patient populations, lab methods, and staining protocols 4.
What to ask your doctor
- Has my tumor been tested for CLDN18.2, and if so, what threshold was used to call it positive?
- What does my CLDN18.2 result mean for my treatment options, including whether zolbetuximab or a clinical trial might be relevant?
- How do my other biomarker results (HER2, PD-L1, MSI/MMR, EBV) fit together with CLDN18.2 to guide my care?
- If my tumor was not tested for CLDN18.2, can it be tested now on existing tissue?
- What side effects should I watch for if anti-CLDN18.2 therapy is considered?
This question is drawn from common patient questions about Oncology and answered using cited medical research. We do not provide individualized advice.