Concordance of claudin-18.2 expression in biopsy, resection, and recurrent specimens: implications for zolbetuximab therapy in pancreatic ductal adenocarcinoma.

Claudin-18.2 is a promising therapeutic target for gastrointestinal cancer. However, its expression pattern in pancreatic ductal adenocarcinoma, especially the concordance between biopsy and resection specimens, is unknown. This study aimed to evaluate the consistency of claudin-18.2 positivity across different specimen types using the clinically validated antibody clone 43-14A employed in ongoing zolbetuximab trials. Immunohistochemical analysis for claudin-18 was conducted on 211 resected pancreatic cancer tissues, 133 matched preoperative biopsy samples, and 60 samples from recurrent lesions. The concordance between the biopsy and resection specimens was 92.5% using a 75% staining threshold. However, this high concordance likely reflects the large proportion of claudin-18.2-negative cases, as the biopsy sensitivity for detecting claudin-18.2-positive tumors was only 54.6%. This raises concerns about underdiagnosis and suggests that biopsy alone may miss patients eligible for zolbetuximab therapy. Receiver operating characteristic analysis showed that lowering the threshold to 20% in biopsy samples improved the sensitivity to 100%. However, patients meeting this threshold would still not qualify for therapy under the current trial criteria, highlighting a potential clinical dilemma. Claudin-18.2 expression was generally preserved in recurrent lesions (83.3% concordance with primary tumors), although reductions were noted in local recurrence and liver metastasis. These findings suggest that although biopsy-based assessments may be a practical initial tool, they should be interpreted with caution. Confirmatory studies on resection specimens using the same clinical trial protocol may be necessary to ensure the accurate identification of patients eligible for claudin-18.2-targeted therapy.