FOS and osteosarcoma: In this study, we set out to perform FOS/FOSB immunohistochemistry, FOS fluorescence in-situ hybridization as well as methylation and copy number profiling of 77 osteoblastomas and to compare our results with fibrous dysplasia cases and a large set of osteosarcomas including conventional, parosteal, central low-grade, periosteal and osteoblastoma-like subtypes.