Dedifferentiated giant-cell tumor of bone with an undifferentiated round cell mesenchymal component

The dedifferentiated giant-cell tumor of the bone is a very rare variant of the giant-cell tumor (GCT). We report the clinical, radiographic and histological findings of a dedifferentiated GCT in which the dedifferentiated component consisted of small round cells. We also comment on previously reported cases of dedifferentiated GCT, discuss the clinical implications of this dual histology, and analyze the information published about the coexistence of similar genetic abnormalities in GCT and small round cell tumors of the bone.