CLDN18.2 expression in resectable gastroesophageal cancers: associated clinical and molecular signatures and impact of neoadjuvant chemotherapy on intra-tumour heterogeneity

Abstract Background Claudin 18.2 (CLDN18.2), a key component of tight junctions, is overexpressed in up to 40% of oesophagogastric adenocarcinoma (OGA) and is a clinically validated biomarker in the unresectable setting. However, data is required in the resectable stages, including chemotherapy effects, relationship with genomic and immune factors, and measures of heterogeneity. Methods CLDN18.2 (ab222512, Abcam) and PD-L1 (E1L3N, Cell Signaling) were assessed by immunohistochemistry on adjacent FFPE slides in 57 patients with resectable OGA. Positivity was defined as 2+/3+ staining in ≥40% of tumour cells for CLDN18.2 and combined positive score (CPS)≥1 for PD-L1. Twenty-four patients (43%) had additional tumour samples to assess CLDN18.2 intra-tumour heterogeneity. Tumour mutational burden (TMB) and copy number aberrations (CNAs) were estimated from WGS and tumour microenvironment (TME) composition from transcriptomic data. Mann Whitney/t-test was used to compare clinical and molecular characteristics, and log-rank test to compare survival curves. Statistical significance was set at p=0.05. Results Fifty-seven patients with resected OGA (79% after neoadjuvant chemotherapy (nCT)) were evaluated. CLDN18.2 was expressed in 18% and CLDN18.2 expression was not associated with clinicopathological features or survival. CLDN18.2 copy numbers (n=57, p=0.24) and RNA levels (n=20, p=0.48) were not associated with staining intensity. Compared to CLDN18.2-ve, CLDN18.2+ve cases did not differ in PD-L1 expression, TMB, CNAs, or TME composition (all p>0.05). However, exposure to chemotherapy was significantly associated with lack of CLDN18.2 (OR=0.2, 95% CI 0.04-0.79, p=0.03) and, among CLDN18.2+ve cases, CLDN18.2 status concordance between tumour samples was 100% in treatment-naïve but only 29% in cases exposed to chemotherapy. Conclusions CLDN18.2+ve and CLDN18.2-ve tumours had similar clinical, genomic and immune features. However, exposure to chemotherapy substantially contributes to CLDN18.2 intra-tumour heterogeneity. Larger cohorts will need to clarify whether the evaluation of multiple tumour samples is required for an accurate assessment of CLDN18.2 expression.