Osteosarcoma is the most common primary malignant bone tumour, excluding myeloma and lymphoma. There is a predilection for the metaphyseal region of tubular long bones. 50% of cases occur around the knee.

Osteosarcoma (osteogenic sarcoma) is a malignant connective (soft) tissue tumor whose neoplastic cells present osteoblastic differentiation and form tumoral bone.

Prevalence

It accounts for 5% of childhood tumors. It has a bimodal distribution, with 75% occurring in patients below the age of 20. A second peak in incidence occurs in the elderly, usually associated with an underlying bone pathology such as Paget's disease, medullary infarct , or prior irradiation.

Pathology

The tumor may be localized at teh metaphyseal end of the long bones. Most often it affects the upper end of tibia or humerus, of lower end of femurus. The tumor is solid, hard, irregular ("fir-tree" aspect on X-ray examination) due to the tumor spicules of calcified bone radiating in right angles. Surrounding tissues are infiltrated. Microscopically: Tumor cells are very pleomorphic (anaplastic), some are giant, numerous atypical mitoses. These cells produce osteoid describing irregular trabeculae (amorphous, eosinophilic/pink) with or without central calcification (hematoxylinophilic/blue, granular) - tumor bone. Tumor cells are included in the osteoid matrix. Cartilage may be present. Presence of immature blood vessels (sarcomatous vessels lacking endothelial cells) favors the bloodstream metastasizing. 1

Symptoms

This type of bone tumor will first appears as a lump in long bones. Musles will start to become weaker as the affected bone part is not as strong as normal bones. Since it is a bone tumor, the feel of it is bony but muscles are not neccesarity attached.

Signs

Treatment

Standard therapy is a combination of surgery and chemotherapy. For periosteal osteosarcoma, only surgery is required.

Prognosis

Canine Osteosarcoma

Osteosarcoma also occurs in dogs and typically afflicts middle aged dogs with long limbs (for example, Greyhounds and German Shepherds). One key difference between osteosarcoma in dogs and humans is that the cancer is far more likely to spread to the lungs in dogs.

External Links

• Treatment Information from U.S. National Cancer Institute
• Excellent review of the imaging features of osteosarcoma
• Atlas of Pathology