Giant-cell tumor of bone

Giant-cell tumor of the bone (GCTOB) is a relatively uncommon bone tumor characterized by the presence of multinucleated giant cells (osteoclast-like cells). Malignancy in giant-cell tumor is uncommon and occurs in about 2% of all cases. However, if malignant degeneration does occur, it is likely to metastasize to the lungs. Giant-cell tumors are normally benign, with unpredictable behavior.

It is a heterogeneous tumor composed of different cell populations. The giant-cell tumour stromal cells (GCTSC) constitute the neoplastic cells, which are from a mesenchymal stem cell origin and are classified based on expression of osteoblast cell markers such as alkaline phosphatase and osteocalcin. In contrast, the mononuclear osteoclast precursor cells giving rise to multinucleated giant cells (MNGC) are secondarily recruited and comprise the non-neoplastic cell population. They are derived from an hematopoietic monocyte/ macrophage lineage determined primarily by expression of CD68, a marker for monocytic precursor cells. In most patients, the tumors are slow to develop, but may recur locally in as many as 50% of cases.