Expression of Claudin 18.2 and its Prognostic Significance in Patients with Japanese Gastric Solid-Type Poorly Differentiated Adenocarcinoma

Background The role of claudin 18.2 in gastric solid-type poorly differentiated adenocarcinoma (PDA) is unknown. In this study, we examined the clinicopathological and prognostic significance of claudin 18.2 expression in solid-type PDA. Methods We retrospectively enrolled 116 participants with primary solid-type PDA. They were categorized according to deficient or proficient mismatch repair (MMR) status (51 and 65 participants, respectively). The expression of claudin 18.2 was assessed by immunohistochemistry and classified into positive or negative expression. We determined the differences in expression status relative to intratumoral location to systematically evaluate patterns of intratumoral expression heterogeneity and MMR status, and the association between expression status, clinicopathological characteristics, and prognoses. Results Positive claudin 18.2 expression was observed in 28 of 116 patients (24%), and most (25/28 patients) showed a heterogeneous expression pattern. The pMMR group showed a significantly higher proportion of claudin 18.2 positive status compared with the dMMR group ( p = 0.028). A log-rank test revealed no significant differences between claudin 18.2-positive and -negative status patients with respect to overall survival (OS) and disease-free-survival (DFS) ( p = 0.343, p = 0.253, respectively). Claudin 18.2-positive status was significantly correlated with longer OS and DFS compared with claudin 18.2-negative status in the pMMR group ( p = 0.046, p = 0.032, respectively), but not with the dMMR group ( p = 0.689, p = 0.623, respectively). Conclusions Claudin 18.2 positive status is significantly correlated to pMMR status. Claudin 18.2-positive status may be a useful prognostic indicator in pMMR-solid-type PDA.