Spontaneous malignant transformation of conventional giant cell tumor.

Spontaneous malignant transformation of conventional giant cell tumor (GCT) of bone is exceedingly rare. We report on a case of GCT of the iliac crest in a 35-year-old woman with malignant change into a high-grade osteosarcoma 10 years after the first appearance of GCT on a radiograph. Since the patient refused therapy for personal reasons the tumor remained untreated until sarcomatous transformation occurred. Image cytometry showed DNA aneuploidy and a suspiciously high 2c deviation index (2cDI) in the primary bone lesion. A thorough review of the world literature revealed only seven fully documented cases of secondary malignant GCT which matched the definition of a "sarcomatous growth that occurs at the site of a previously documented benign giant cell tumor" and not treated by radiotherapy. These cases as well as the current one suggest that a spontaneous secondary malignant GCT presents as a frankly sarcomatous tumor in the form of an osteosarcoma or malignant fibrous histiocytoma. It usually appears at sites of typical GCTs-often without any recurrent intermediate state-and is diagnosed 3 or more years after the primary bone lesion. The prognosis is poor.