MKI67 and neoplasm: Accordingly, GC3 PDOs and the primary tumor tissue were subjected to immunohistochemical (IHC) staining for the GC marker carcinoembryonic antigen (CEA), the cell proliferation marker Ki-67, the gastrointestinal stem cell marker leucine-rich repeat-containing G protein-coupled receptor 5 (LGR5), and the epithelial cell marker E-cadherin.