CD133, (PROM1) is a transmembrane protein (Corbeil et al., 2001; Shmelkov et al., 2005) that is widely used as a cell-surface marker for stem cell and cancer stem cell populations (Bussolati et al., 2005; Lee et al., 2005; Tirino et al., 2008; Zhang et al., 2008). The gene discussed is PROM1; the disease is cancer.