CD13 is a marker for slow-growing CSCs in vivo. a) FACS analysis of a xenograft tumor produced by Li-7 cells showed an association of CD13 expression with other CSC markers (left: EpCAM, middle: CD133, right: CD24). b) Immunohistochemical localization of CD13(+) cells in xenograft tumors. Some parts of the tumor stained (red arrow) but cells in mitosis were unstained (yellow arrow). c) Ki-67 (right) and CD13 (middle) expression and hematoxylin and eosin staining (left) of a xenograft tumor showed absence of Ki-67 staining in morphologically undifferentiated CD13(+) cells near the vessels (black arrow).