ALDH1A1 and colonic neoplasm: Research suggests that there are several subpopulations of stem cells that reside within a tissue.25 Therefore, we looked specifically at CD166 expression since it is known that this is another marker for identification of colon cancer stem cells.26,27 We see that CD166 and ALDH1 identify different sub-populations of colon CSCs as immunostaining marks distinct subsets of cells.