CD44 and neoplasm: The use of the CD44+/CD24-/low/lin- phenotype and another marker, the ALDEFLUOR assay, which measures the Aldehyde dehydrogenase enzymatic activity, demonstrated that cells able to initiate tumor in mice were within the ALDEFLUOR-positive cells, the cells displaying both phenotypes being the most tumorigenic, and that none of the CD44+/CD24-/low/lin- cells without ALDEFLUOR activity could grow in mice [20].