In the context of cancer, a small, distinct subpopulation of cells within tumors termed “cancer stem cells” (CSCs), tumorigenic cells, or cancer-initiating cells has been identified in several tumor types (43), including breast cancer (CD44+CD24−/lowlineage− and Aldefluor+ cell fractions), colon cancer (CD133+ cells), and cervical cancer (CD66+ cells). This evidence concerns the gene CD44 and cancer.