Osteosarcoma is a malignant tumor of bone which is characterized by osteoid production by neoplastic cells. There are numerous subtypes of osteosarcoma (ie. telangiectatic, extraosseous, periosteal, small cell, etc.), but this case focuses on the conventional intramedullary type. It is a disease of growing teenagers and young adults with the majority of patients afflicted before the age of 30. There is a male predilection. Patients typically present with a complaint of longstanding pain (sometimes following trauma) and soft tissue swelling, but rarely with pathological fractures. The metaphyses of long bones are usually affected in the younger patients (<30 years old). A second peak incidence occurs in patients greater than 60 years of age but these lesions usually occur in people with a predisposing condition (ie. Paget's Disease, osteogenesis imperfecta, chronic osteomyelitis, bone infarcts, previous radiation). The axial skeleton is typically involved in these cases. There are several lesions which can mimic osteosarcoma pathologically,such as osteoblastoma, chondrosarcoma with enchondral ossification, giant cell tumors, and even a fracture callus.
Osteosarcomas readily metastasize to the lungs and it is common to have lung involvement at the time of presentation. Prognosis was poor prior to effective chemotherapeutic agents (10-20% five year survival) but has recently improved to 70-80% cure rates if the tumor is surgically resectable and there are no metastases at presentation. Greater than 95% tumor necrosis following pre-operative chemotherapy is considered to be the most significant indicator for a favorable prognosis. Other factors such as age, underlying conditions, and surgical resectability are also important. The predominent stromal component does not appear to have prognostic significance.
The gross and microscopic appearances of osteosarcomas are similar to the case lesion. The predominant stromal component may vary (ie. osteoblastic, fibroblastic, chondroblastic, or telangiectatic), but the presence of neoplastic cells producing osteoid represents an osteosarcoma.
Osteosarcomas are not simple, straightforward tumors. They have numerous variants and must be differentiated from other, often benign, lesions which are similar in appearance.
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Contributed by David Sholehvar,MD and Karen Schoedel, MD