Dedifferentiated chondrosarcoma with a noncartilaginous component mimicking a conventional giant cell tumor of bone

We report a case of dedifferentiated chondrosarcoma in which the dedifferentiated component of the tumor shows a close histologic resemblance to a conventional giant cell tumor of bone. The tumor affected a 30-year-old woman with a long history of left shoulder discomfort and limitation of motion. Radiographic studies revealed a biphasic destructive lesion in the left proximal humerus composed of high-signal lobulated component on T2-weighted magnetic resonance image accompanied by a low signal intensity component exhibiting destructive growth with extension into soft tissue. Microscopically, two different areas consisting of the chondroid tissue and nonchondroid giant cell-rich lesion resembling conventional giant cell tumor of bone were found. Considering that the prognosis and survival associated with these two entities are very different, it is important to be aware of this variant of dedifferentiated chondrosarcoma to avoid the misdiagnosis of conventional giant cell tumor of bone.