CLDN18 identifies high-risk precursor lesions in gallbladder carcinogenesis: A study of the TFF2⁺ pseudopyloric metaplasia to intestinal metaplasia axis.

The pathogenesis of gallbladder adenocarcinoma(GBC) remains inadequately elucidated. While its association with intestinal metaplasia (IM) has been acknowledged, there is a paucity of evidence connecting GBC to the most prevalent metaplastic type-pseudopyloric metaplasia (PPM). Given the morphological similarities between PPM and spasmolytic polypeptide-expressing metaplasia (SPEM), a recognized gastric precancerous condition, we propose that trefoil factor 2 (TFF2)-positive PPM may represent a cellular origin of GBC. Furthermore, we examine the role of the emerging therapeutic target claudin-18 (CLDN18) in this context. Through immunohistochemistry (IHC) analysis of 37 GBC, 30 biliary intraepithelial neoplasia (BilIN), 20 intracholecystic papillary neoplasm (ICPN), 26 IM, and 20 PPM samples, we observed an inverse correlation between CLDN18 expression and vascular invasion, whereas TFF2 expression was positively associated with tumor differentiation. CLDN18 overexpression(a staining intensity ≥ 2 + in ≥ 75% of tumour cells) was identified in 18.9% of GBC cases. This study provides the first evidence that CLDN18 is specifically activated at the precursor stage of gallbladder carcinogenesis, being strictly confined to lesions with an intestinal phenotype (IM, BilIN, ICPN) while remaining entirely negative in normal epithelium and PPM. This "all or none" expression pattern establishes CLDN18 as an ideal biomarker for identifying high risk gallbladder precursor lesions, particularly for recognizing PPM that has undergone malignant prone intestinal differentiation. Furthermore, the subset of GBCs with high CLDN18 expression identifies patients who may benefit from CLDN18 targeted therapies.