CD44 and gastric cancer: To clarify the role of Bmi-1 in stemness of gastric cancer, we checked the expression of Bmi-1 in microsphere and found that sphere cells from SGC7901 and MKN45 cell lines overexpressed Bmi-1 and other stem cell markers Oct-4, Sox2, Nanog, CD44, and CD133 (Fig. 1a and Additional file 2: Figure S1).