Real-world data on CLDN18.2 expression in gastric and gastroesophageal cancer patients.

e16038 Background: Gastric cancer (GC) and gastroesophageal junction cancer (GEJC) are highly lethal malignancies that are frequently diagnosed at advanced stages, where treatment is more challenging and prognosis remains poor. CLDN18.2 has emerged as a therapeutic target in GC and GEJC, with the FDA approval of an antibody combined with fluoropyrimidine–platinum chemotherapy for first-line treatment of locally advanced or metastatic HER2-negative, CLDN18.2-positive G/GEJ tumors. The aim of this study is to report the proportion of CLDN18.2-IHC positive samples in patients with GC and GEJC. Methods: A retrospective analysis was conducted in data from a cohort of 152 patients with GC/GEJC and other types pf carcinomas who were assessed for CLDN18.2 positivity by IHC with the VENTANA CLDN18(43-14A) RxDx Assay. CLDN18.2 positivity was defined as ≥ 75% of viable tumor cells demonstrating moderate to strong (2+/3+) membranous CLDN18 staining. Results: CLDN18.2 positivity was identified in 38 of 120 (31.6%) patients with gastric adenocarcinoma and in 7 of 26 (26.9%) patients with GEJ adenocarcinoma, while no positivity was observed among patients with other types of carcinomas (0/6). Conclusions: The findings of this study indicate that a substantial proportion of patients with GC or GEJC are CLDN18.2-positive and may be eligible for targeted therapy in combination with chemotherapy. This therapeutic approach has been shown, in clinical trials, to improve progression-free and overall survival compared with standard chemotherapy.