PROM1 and medulloblastoma: CD133, a cell surface membrane glycoprotein encoded by the PROM1/PROM2 genes17, 18, is a cell surface marker of both normal stem/progenitor cells (including normal endothelial cells) and neoplastic tumor stem cells (such as medulloblastoma, glioblastoma, prostate, and colon cancer)17, and is expressed in the human embryo during the early stages of vascular development (4-week embryo)19.