Wnt Signaling Shapes the Histological Variation in Diffuse Gastric Cancer.

Abstract Background & Aims Diffuse type gastric cancer is currently subdivided into signet-ring cell carcinoma (SRCC) and non-SRCC referred to as poorly cohesive carcinoma not otherwise specified (PCC-NOS). Although these subtypes are considered to be independent, they often co-exist in the same tumors, raising a question whether they clonally differ or not. To tackle this question, we established an experimental platform for human diffuse gastric cancer that enables accurate modeling of histological subtypes. Methods Seven patient-derived diffuse gastric cancer organoid lines were established characterized by histopathological analysis, in situ hybridization and gene expression analysis. For genetic modeling of diffuse gastric cancer, we knocked out CDH1 and/or TP53 in human normal gastric organoids. GFP-labeled gastric cancer organoids were xenotransplanted into immune-deficient mice for in vivo assessment. Results PCC-NOS organoids transformed into SRCC-like structures upon removal of Wnt and R-spondin from the culture medium. This morphological change paralleled downregulation of Wnt-target and gastric stem cell genes including LGR5, and elevation of differentiation markers, such as KRT20 and MUCs. The association between Wnt target gene expression and histological subtypes was confirmed in three patient-derived gastric cancer tissues. In vivo, single clone-derived organoids formed tumors that comprise two distinct histological compartments, each of which corresponding to SRCC and PCC-NOS. The transition from PCC-NOS to SRCC histology reflected the abundance of surrounding R-spondin-expressing fibroblasts. Conclusions SRCC and PCC-NOS were clonally identical, and their morphology was regulated by extracellular Wnt and R-spondin expression. Our results decoded how genetic mutations and the tumor environment shape pathohistological and biological phenotypes in human diffuse gastric cancers.