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Osteosarcoma is a malignant tumor of the bone and arises from mesenchymal cells. The malignant cells are usually pleomorphic spindle cells that lay down abnormal bone (osteoid formation).
- Osteosarcoma is the most common pediatric primary bone cancer and is the 8th most common malignancy of childhood.
- A bimodal distribution is noted with the first peak in adolescence (median, age 16 years) and second peak during the 7th and 8th decade of life.
- Incidence of osteosarcoma parallels skeletal growth and is more frequently noted in tall individuals.
- Males are more commonly affected than females.
- In the United States, there are about 4.4 cases per million children and adolescents.
- Approximately 400 new pediatric cases of osteosarcoma are diagnosed each year in the United States.
- Radiation exposure
- Hereditary retinoblastoma, in which patients with germline Rb gene mutation have increased risk of osteosarcoma with or without radiation exposure.
- Li-Fraumeni syndrome, in which patients have germline TP53 gene mutation and increased risk of a range of sarcomas, among other malignancies
- Rothmund-Thomson syndrome
- Bloom syndrome
- Hereditary multiple exostoses
- Fibrous dysplasia
- Paget disease of the bone, although less relevant to pediatric populations
- The histologic hallmark of osteosarcoma is the presence of osteoid.
- Most cases of pediatric osteosarcoma are high-grade cancers, although lower grade variants are seen.
- No classic genetic change, although karyotypes are typically highly abnormal
- Major subtypes of osteosarcoma include osteoblastic, chondroblastic, fibroblastic, telangiectatic, and small cell.
- At diagnosis, 80% of patients will have localized disease and 20% will have metastatic disease.
- In 80% of tumors, the metaphysis of long bones will be involved, such as the femur, tibia, and humerus, with distal femur the most common primary site. In 20% of tumors, other sites of involvement will include the pelvis, facial bones, and shoulder blade.
- The most common sites of metastatic disease are lungs and bone. Involvement of regional lymph nodes is rare.
- The etiology of most cases is unknown.
- Abnormal TP53 and/or Rb function implicated in laboratory studies of osteosarcoma
- Radiation exposure is a known cause of osteosarcoma and usually presents 10–20 years after exposure.