POU5F1 promoter driven GFP expression in a transiently transfected cell line derived from an osteosarcoma biopsy has been used to identify tumorigenic cells [21] However, in another study, expression of POU5F1, SOX2, and NANOG was reported to either increase significantly or remain unchanged in sphere cultures as compared with non-TSC enriched cultures of Os 99-1, Saos-2, MG-63, and HuO9 osteosacroma cell lines [5]. This evidence concerns the gene POU5F1 and osteosarcoma.