Tan-white and gritty with areas of necrosis, hemorrhage and cystic degeneration. The tumor frequently grows through the cortical bone and raises the periosteum. The triangular space thus generated between the raised periosteum and the edge of the bone can be seen radiographically. This triangle is often referred to as the Codman's triangle. The histological feature pathognomonic of osteosarcoma is the production of neoplastic osteoid matrix.
Tumor cells are osteocytes or osteoblasts and resemble normal osteoblasts.
However, bizarre cells and atypia are invariably seen. Other types of matrices, such as cartilage, are frequently seen. Diseases that increase bone remodeling, such as Paget's disease, increase frequency of this malignancy. Osteosarcomas typically present as painful enlarging lesions. In some cases, fracture of a bone on relatively minor trauma may be the first symptom of osteosarcoma.