Parosteal Osteosarcoma

Higher magnification of the previous image. The spindle cell proliferation is more cellular than that seen in the previous example (images 52-54); however, it still lacks atypia or increased mitotic activity. Dedifferentiation does occur in a small number of cases and it significantly worsens the prognosis. In the absence of dedifferentiation, wide local excision is the treatment of choice. Long-term survival rates are in the range of 80% to 90%.