Three main BCSC subpopulations have been identified using the CD44+CD24−/low phenotype and high aldehyde dehydrogenase (ALDH+) activity, i.e., ALDH−CD44+CD24−/low enriched mesenchymal-like BCSCs (located along the tumor-invasive edge), ALDH+non-CD44+CD24−/low enriched epithelial-like BCSCs (located centrally within a tumor), and highly purified ALDH+CD44+CD24−/low BCSCs with both mesenchymal and epithelial characteristics are considered to be the most tumorigenic (Liu et al., 2014; Liu et al., 2018; Abdoli Shadbad et al., 2021). The gene discussed is CD44; the disease is neoplasm.