PROM1 and neoplasm: CD133 has been shown to mark a subpopulation of tumor cells characterized by high levels of stemness genes, higher clonogenicity and in vitro self-renewal, and increased in vivo tumorigenicity than the CD133- subpopulation in several STS, including SS (135–137), RMS (49, 50, 52, 138) and FS (77, 78, 136).