CD44 and gastric cancer: To explore the role of Mel-18 in gastric CSCs, we firstly detected the expressions of Mel-18 and stem cell markers or related proteins CD44, CD133, Oct4, Sox2, and Gli1 [17] in samples of 101 primary lesions of gastric cancer using immunohistochemical (IHC) assay (Supplementary Figure S1), and analyzed the correlations between Mel-18 and these stem cell markers.