(A-B) Human primary colorectal adenomas labeled with antibodies to CD166 show (A) cell surface expression (white, arrowheads) or (B) cytoplasmic expression (brown, arrow). (C) Human colorectal liver metastasis that has both cell surface and cytoplasmic expression of CD166 (brown, arrow). Methyl Green nuclear counterstain (green). (D) Benign mouse intestinal tumor labeled with antibodies to CD166 (white, arrowheads) and Hoechst nuclear counterstain (blue). (Ea-Eb) Human primary colorectal adenoma co-stained with antibodies to CD44 (red) and CD166 (white). (Eb) Subpopulations of tumor cells express both CD44 and CD166 (merged, light blue, white arrows), or only CD44 (red staining, red arrowheads). Some tumor cells do not express CD44 but express CD166 (white staining, white arrowheads). (Fa-Fc) Mouse adenoma stained with antibodies to CD166 (white) and ESA (red). Subpopulations of cells express CD166 and ESA (merged, light blue, white arrow), ESA alone (red arrowhead) or CD166 alone (white arrowhead). Bar=25μm.