A high grade malignant bone-forming mesenchymal neoplasm producing osteoid. The tumor arises from the medullary portion of the bone. It affects the long bones and most commonly, the distal femur, proximal tibia, and proximal humerus. Pain with or without a palpable mass is the most common clinical presentation. It usually has an aggressive growth and may metastasize through the hematogenous route. The lung is the most frequent site of metastasis. [from
NCI]