Variability in morphology and immunohistochemistry of Crohn's disease-associated small bowel neoplasms: implications of Claudin 18 and Cadherin 17 expression for tumor-targeted immunotherapies.

Aims: Inflammatory bowel disease-associated colorectal carcinomas are known to have different morphology, immunoprofile, and genetic findings from sporadic colorectal carcinomas; however, little is known for Crohn's disease-associated small bowel neoplasms (CD-SBNs). Cadherin 17 is a useful biomarker of adenocarcinomas with intestinal phenotype and recently reported as an ideal target for chimeric antigen receptor T-cells (CAR-T) therapy for gastrointestinal carcinoma. Claudin 18 is a cell adhesion protein, and Claudin18 isoform 2 (CLDN18.2) is frequently expressed at high levels in gastric-type adenocarcinoma. Zolbetuximab, a targeted monoclonal antibody, has been developed for CLDN18.2-positive gastroesophageal adenocarcinoma. We examined a series of CD-SBNs for both Cadherin 17 and Claudin 18, and also hypothesized that expression of Claudin 18 was associated with gastric phenotype.

Methods and results: We performed histological and immunohistochemical examinations on 25 CD-SBNs. Most of adenocarcinomas showed tubular morphology as seen in gastric carcinomas, whereas a subset of dysplasia was morphologically similar to that of the large bowel. Cadherin17 and Claudin 18 expression was identified in 93% and 57% CD-associated adenocarcinomas respectively. In Cadherin 17-positive CD-SBNs, frequent MUC5AC, MUC6, and Claudin18 expression was identified (61%, 57%, and 57%, respectively). Claudin 18-positive CD-SBNs showed significantly more MUC5AC and MUC6 expression than Claudin 18-negative CD-SBNs (P = 0.005, < 0.001 respectively).

Conclusion: In CD-associated small bowel adenocarcinomas, Cadherin 17 expression was frequently retained and Claudin 18 was frequently co-expressed. Claudin 18 had a positive correlation with the expression of gastric mucins. These results suggest that CD-associated small bowel adenocarcinomas may be candidates for Cadherin 17- and Claudin 18-targeted immunotherapies.