SOX2 and sarcoma: Although the first studies suggested prominin-1 (CD133) [3,4] or nestin [3] as rhabdomyosarcoma CSC markers, our recent study showed that, regardless of these proteins, only sarcoma cell lines that express high levels of the transcription factor SOX2 form tumors in immunodeficient NOD/SCID gamma (NSG) mice [5].