Locally aggressive tumor composed of giant cells that arise from the bone marrow.

Peak incidence: 20-40 years

Localization: Epiphyseal/metaphyseal region of the long bones (predominantly bones close to the knee)

Symptoms:- Local pain and swelling- Limited range of motion- Pathological fractures

Diagnostics:- X-ray: multicystic osteolytic lesions ("soap bubble appearance")- Histopathology: multinucleated giant cells

Treatment: curettage and bone grafting, or en bloc resection to minimize reccurence rate