To clarify the character of cancer stem cells in the CD44v9-expressing cells, we further examined the expression of cancer stem cell markers.7 We observed elevated expression of Sox2 and ABCG2, but not of CD24, in the CD44v9-positive cells (Supplementary Fig. 5B), while CD133 levels were low and could not be detected in CD44v9-positive and CD44v9-negative cells (data not shown). Here, ABCG2 is linked to cancer.