Bone tumor arising from epiphyses is

Giant cell tumor refer Robbins page no 1233 Pathogenesis. Current evidence suggests that the neoplas- tic cells of giant cell tumor are primitive osteoblast precur- sors but they represent only a minority of the tumor cells. The bulk of the tumor consists of non-neoplastic osteoclasts and their precursors. The neoplastic cells express high levels of RANKL, which promotes the proliferation of osteoclast precursors and their differentiation into mature osteoclasts RANK expressed by these cells. However, the feedback between osteoblasts and osteoclasts that nor- mally regulates this process during bone remodeling is absent. What results is a localized but highly destructive resorption of bone matrix by reactive osteoclasts. Giant cell tumors arise in the epiphysis but may extend into the metaphysis. The majority arise around the knee (distal femur and proximal tibia), but viually any bone can be involved. The typical location of these tumors near joints frequently causes ahritis-like symptoms. Occa- sionally, they present with pathologic fractures. Most are solitary;