Dynamic changes of claudin 18.2 expression after systemic therapy in gastric and esophagogastric junction cancer

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BACKGROUND: Claudin 18.2 (CLDN18.2) is a promising therapeutic target in gastric/esophagogastric junction adenocarcinoma (GC/EGJC), but its dynamic expression during systemic therapy is unclear. METHODS: CLDN18.2 expression by immunohistochemistry in paired tumor samples from 155 patients with advanced GC/EGJC was retrospectively evaluated before and after systemic therapy. CLDN18.2-positive was defined as ≥75% of viable tumor cells exhibiting moderate-to-strong (2+ or 3+) membranous staining. RESULTS: Among all patients, 54 (34.84%) were CLDN18.2-positive. Following treatment, the proportion of CLDN18.2-positive patients increased significantly to 61 (39.35%) (p < .001). Among patients who were CLDN18.2-negative at baseline, 57 (56.44%) showed increased expression after treatment, including 22 (21.78%) who converted to positive status. In contrast, among those CLDN18.2-positive at baseline, expression decreased in 35 patients (64.81%), with 15 (27.78%) converting to negative status (p < .001). Among patients receiving chemotherapy alone (n = 25), 1 (4.00%) converted to negative and 5 (20.00%) converted to positive, whereas among those receiving chemotherapy combined with immunotherapy (n = 130), 14 (10.77%) converted to negative and 17 (13.08%) converted to positive (p = .45). A total of 131 patients (84.52%) demonstrated changes in CLDN18.2 expression following therapy, encompassing both conversions across the positivity threshold and fluctuations within the same classification. CONCLUSION: CLDN18.2 expression in GC/EGJC is dynamic and frequently altered after systemic therapy. These findings support reassessment of CLDN18.2 status before initiating CLDN18.2-targeted therapies.