<B>Osteosarcoma </B>

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Osteosarcoma

Etiology:

• Patients with mutations in the retinoblastoma gene have a several hundred fold greater incidence of osteosarcoma.

Pathogenesis:

• As with most malignancies, the precise pathogenesis is unclear.
• The disease is associated with mutations in the retinoblastoma (Rb) gene, and deletions of or mutations in the p53 gene.
• Other conditions that are associated with high bone turnover, such as Paget's disease and fibrous displasia of bone predispose to the development of osteosarcoma.
• The tumor commonly arises during the time of maximal bone growth (late adolesence).

Epidemiology:

• Most common primary malignant tumor of bone.
• More commonly seen in men (about 2-1).

General Gross Description:

• Arise from the metaphysis of long bones.
• Often big, bulky tumors.
• Tan-white in color with a gritty appearance and 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.

General Microscopic Description:

• The histological feature pathognomonic of osteosarcoma is the production of neoplastic osteoid matrix.
• Tumor cells are osteocytes or osteoblasts and resemble normal osteoblasts.However, bizzare cells and atypia are invariably seen.
• Other types of matrices, such as cartilage, are freqently seen.

Clinical Correlations:

• Most frequently arise near the knee joint; secondly most frequently near the hip joint.
• Diseases that increase bone remodeling, such as Paget's disease, increase frequency of this malignancy.
• Other "benign" tumors of bone and fibrous dysplasia; also, may dispose to osteosarcoma.
• 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.
• As is true of most sarcomas, osteosarcoma spreads predominantly by the blood stream.
• Approximately 20% of patients have pulmonary metastases at the time of diagnosis.
• Current long-term survival (five year survival rates)are in the range of 60%.

References:
•Robbins "Pathologic Basis of Disease". (Cotran, Kumar and Robbins Eds). 5th Edition. pp 1234.