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Giant cell tumor
Etiology:

• Not known.
Pathogenesis:

• Unknown.
Epidemiology:

• Usually arise in the third to the fifth decade of life.
• Slightly more common in females.
General Gross Description:

• Giant Cell Tumor of Bone: Also called Osteoclastoma
• Tumors are usually large and distinctly red colored.
• Areas of hemorrhage and cystic degeneration are frequent.
General Microscopic Description:

• Histologically, the tumor is composed of mononuclear cells and many multinucleate cells, often with 40 to 100 nucleii.
• The nucleii of the mononuclear cells and the giant cells are identical.
• This is an important distinguishing feature of this tumor from other giant cell containing tumors and other lesions of bone, such as pigmented villonodular synovitis, or hyperparathyroidism.
• There is often evidence of recent and old hemorrhage (indicated by hemosiderin deposits).
• Some reparative bone formation can be seen in older lesions.
Clinical Correlations:

• Locally aggressive tumor; usually does not metastasize distally.
• Tumors are most common around the knee joint, but any other bone may be involved.
• Symptoms are usually related to the involvement of the joint, including pain and restriction of movement.
• Occassionally, the patient may present with a fracture.
• X-ray examination of affected bone shows a clear lytic lesion that often erodes through the cortical bone into the neighboring soft tissue.
• There is usually no sclerotic rim around the tumor.
• The tumor has a tendency to local recurrence after conservative treatment.
References:
•Robbins "Pathologic Basis of Disease". (Cotran, Kumar and Robbins, Eds.) 5th Edition. pp 1245.