CD44 and colorectal cancer: Although our hypothesis is that Akt expression and its signaling activity are increased during the development and metastasis/recurrence of colorectal cancer, total Akt levels were not changed in more tumorigenic spheroid-forming CSCs due to the following limitation of our in vitro culture model of colorectal CSCs: our in vitro models of colorectal CSCs are 3D-sphere-forming culture system or sorted cell culture system with putative CSC-marker (CD44 and CD133) of same colon cancer cell line (HCT116), whose expression levels of total Akt were not altered during 3D culture or cell sorting.