Benign giant cell tumor of bone with osteosarcomatous transformation (''dedifferentiated'' primary malignant GCT): Report of two cases

It is not uncommon for sarcomatous transformation of giant cell tumor (GCT) of bone to occur af?er radiation, but rarely does malignant transformation occur spontaneously, with less than 5 cases reported up to 1995. Only four of these cases have been documented in detail, We report two additional cases of GCT of bone spontaneously transforming or ''dedifferentiating'' into osteosarcoma without radiation therapy. The first case is absolutely unique and most interesting in that the dedifferentiation process occurred in one of multiple GCT lung metastases 6 years after successful eradication of a primary tibial tumor. The right lung was resected due to development: of a large tumor, and at pathologic examination, demonstrated several small nodules of conventional GCT and a much larger, 14-cm mass composed of a mixture of GCT and high-grade osteosarcoma. The second case involved a physician, who had a large tumor in the sacrum with vague symptoms for 8 years. Open biopsy revealed conventional, benign GCT of bone with a secondary aneurysmal bone cyst. Complete curettage 2 weeks later revealed, in addition to areas of conventional, benign CCT a second component of very high grade osteosarcoma. Both patients died less than 1.5 years from diagnosis. This report of osteosarcomatous transformation of a conventional GCT of bone strengthens the theory that there is a mesenchymal cell line in CCT that may spontaneously tansform to sarcoma.