A conventional osteosarcoma characterized by the presence of spindle shaped cells. The disease is Monarch Disease Ontology identifier MONDO_0004301 (fibrosarcomatous osteosarcoma). Also known as: fibroblastic osteogenic sarcoma, fibroblastic osteosarcoma, fibroblastic osteosarcoma (morphologic abnormality), fibrosarcomatous osteogenic sarcoma.