ABCG5 and colorectal cancer: In a previous immunohistochemical study on colorectal cancer from the several potential CSC markers (ABCG5, ALDH1, CD24, CD44, CD90, CD133, EpCam) that have been proposed for solid tumors, only ABCG5 expression in tumor budding cell was found to be associated with poor survival of the patients (Ellenrieder et al., 2001; Visvader and Lindeman, 2008).