Comprehensive Profiling of Claudin 18.2 Immunohistochemical Expression in 564 Surgically Resected Gastric and...

Claudin 18 isoform 2 (CLDN18.2) is a novel therapeutic target for advanced, HER2-negative gastric/gastroesophageal junction (GEJ) adenocarcinoma positive for CLDN18.2 immunohistochemical (IHC) expression, defined as ≥75% tumor cells with moderate-to-strong membranous staining. Clinical studies for emerging CLDN18.2-targeted therapeutics have used less stringent enrollment criteria to test the efficacy of such therapies in patients with moderate-to-low CLDN18.2 IHC expression. Anticipating the advent of such treatments, this study aimed to provide a comprehensive survey of CLDN18.2 expression using a clinical trial-validated CLDN18.2 monoclonal antibody in surgically resected gastric/GEJ adenocarcinomas and characterize CLDN18.2-positive carcinomas using both high- and low-expression thresholds. Crisp membranous CLDN18.2 staining was detected in 59% (335/564) carcinomas, including 57% (164/286) of gastric and 62% (171/278) of GEJ adenocarcinomas. Most gastric (147/164, 90%) and GEJ (166/171, 97%) adenocarcinomas with staining demonstrated moderate or strong staining intensity. Using the high-expression threshold (≥75% tumor cells with moderate-to-strong staining), positive CLDN18.2 expression was observed in 20% (57/286) of gastric and 27% (75/278) of GEJ adenocarcinomas and was associated with Epstein-Barr virus status (P < .001) and stage I gastric adenocarcinomas (P = .02) but stage IV GEJ adenocarcinomas (P = .03). Using a low-expression threshold (≥10% tumor cells with membranous staining), positive CLDN18.2 remained significantly associated with stage I (P = .004) and showed an unadjusted association with improved disease-specific survival in gastric adenocarcinomas (P = .045), which was not retained in multivariable analysis. Whole transcriptomic analysis showed concordance between IHC and CLDN18 messenger RNA expression. Transcriptomic alterations in CLDN18.2 IHC-positive gastric adenocarcinomas included pathways in drug resistance and tumor invasion. In summary, our study presents a detailed characterization of the prevalence and distribution of CLDN18.2 IHC expression patterns. Our results showed that 59% surgically resected gastric/GEJ adenocarcinomas exhibited CLDN18.2 staining. CLDN18.2 IHC positivity defined by both high- and low-expression thresholds may be associated with early-stage gastric adenocarcinoma. These findings expand our recognition of patients who may benefit from CLDN18.2-targeted therapy.