Though further research is needed, our study suggests that tumor samples collected by biopsy or resection and from primary or metastatic sites can be reliably used to screen for CLDN18.2 positivity, defined as ≥ 75% of tumor cells demonstrating moderate-to-strong membranous CLDN18 staining using the VENTANA CLDN18 (43-14A) RxDx Assay (for Investigational Use Only; VMSI/Roche), in patients with LA unresectable or mG/GEJ adenocarcinoma. Here, CLDN18 is linked to neoplasm.