POU5F1 and osteosarcoma: De-differentiated malignant cells acquired CSC-like properties, including self-renewal ability [158, 185, 186], multipotency [186], tumorigenicity [158, 183, 186], invasiveness/metastatic potential [183–186] as well as expression of essential stem cell factors: Notch in neuroblastoma [183], Oct4, c-Myc and Nanog in glioblastoma [158], Oct4 and Sox2 in ovarian cancer [185], and Oct4 Sox2 and Nanog in osteosarcoma studies [186].