These include cancer stem cell (CSC) markers: (i) surface receptors, including EpCAM/CD326 [6,10,29], CD44 variants [100], Notch-ligand Dll4 [101], prominin/CD133 [102], (ii) extracellular ligands, including Wnt [103], and (iii) functional enzymes (ALDH and MMPs) [7,8]. The gene discussed is CD44; the disease is cancer.