Immunohistochemical expression of Claudin18.2 in borderline and malignant gynecologic tumors: Results from a pilot study

Background Claudin 18.2 (CLDN 18.2) is an emerging therapeutic target in gastrointestinal malignancies, but its expression in gynecologic mucinous tumors remains poorly characterized. Our study aimed to evaluate CLDN18.2 expression in borderline and malignant mucinous tumors of the female genital tract and to explore its potential clinical relevance. Methods Formalin-fixed paraffin-embedded tumor specimens from 20 patients with mucinous tumors of the ovary, corpus uteri, or cervix uteri treated between 2013 and 2024 were included. CLDN18.2 expression was assessed by immunohistochemistry (IHC) and scored using the H-score system based on standardized digital evaluation. Clinical data, including tumor stage, grade, and outcomes, were retrospectively obtained. Associations between CLDN18.2 expression and clinicopathologic parameters were analyzed descriptively using SPSS. Results CLDN18.2 expression was detectable in 50.0% of evaluable tumors. Among histologic subtypes, 60% mucinous borderline tumors and 46.2% mucinous adenocarcinomas were positive. Staining intensity was generally mild to moderate, with strong expression (H-score > 200) observed in only one case. No statistically significant associations were observed between CLDN18.2 positivity and tumor stage, grade, patient demographics, or borderline versus invasive status; however, the small sample size limits the interpretability of these findings. Conclusions CLDN18.2 is expressed in a subset of gynecologic mucinous tumors, but high-level expression is uncommon. Given the limited number of cases, these preliminary results should be interpreted with caution, and no firm conclusions regarding clinical correlations can be drawn. Only a minority of patients may meet thresholds for CLDN18.2-targeted therapies established in gastrointestinal malignancies. Larger, multicenter studies are warranted to better define the prevalence, biological significance, and potential therapeutic relevance of CLDN18.2 in these tumors.