The expression of the tight junction protein and therapeutical target Claudin 18.2 is heterogeneously distributed within esophageal and gastric adenocarcinoma

Abstract

Abstract Claudin 18.2 (CLDN18.2) is a therapeutically relevant biomarker in esophageal (EAC) -and gastric adenocarcinoma (GAC). Little is known about its heterogeneity within the primary tumor and corresponding metastases and how many biopsies are needed to determine the true CLDN18.2 status of a tumor. CLDN18.2 was assessed in 1,283 patients (822 EAC, 461 GAC), using the antibody clone 43–14 A. Eight virtual endoscopic biopsies were taken from digitized whole tumor blocks. 204 of 822 EAC (24.8%) and 132 of 461 GAC (28,6%) were positive for CLDN18.2. In GAC, CLDN18.2 expression showed a trend towards less invasive growth ( p  = 0.02) and less common lymph node metastasis ( p  = 0.07) and was more often observed within the EBV-associated subtype ( p  = 0.01). When comparing the expression in one biopsy with the whole tissue section, the sensitivity for CLDN18.2 was low (58.8%). The sensitivity increased to a maximum of 76.5% with 6 and 8 biopsies (positive likelihood ratio = 17.8). Discordant expression between primary tumor and corresponding local lymph node metastasis was observed in 18.5%. This study highlights that CLDN18.2 is a heterogeneously expressed biomarker, within the tumor tissue as well as in primary tumor and corresponding lymph node metastasis. In case of CLN18.2-negative results the representativity of the biopsies must be critically assessed and a re-biopsy might be recommendable.