BENIGN GIANT-CELL TUMOR OF BONE WITH OSTEOSARCOMATOUS TRANSFORMATION (DEDIFFERENTIATED PRIMARY MALIGNANT GCT) - REPORT OF 2 CASES

It is not uncommon for sarcomatous transformation of giant cell tumor (GCT) of bone to occur af?er radiation, but rarely does malignant tran sformation occur spontaneously, with less than 5 cases reported up to 1995. Only four of these cases have been documented in detail, We repo rt 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 dedif ferentiation process occurred in one of multiple GCT lung metastases 6 years after successful eradication of a primary tibial tumor. The rig ht lung was resected due to development: of a large tumor, and at path ologic examination, demonstrated several small nodules of conventional GCT and a much larger, 14-cm mass composed of a mixture of GCT and hi gh-grade osteosarcoma. The second case involved a physician, who had a large tumor in the sacrum with vague symptoms for 8 years. Open biops y revealed conventional, benign GCT of bone with a secondary aneurysma l bone cyst. Complete curettage 2 weeks later revealed, in addition to areas of conventional, benign CCT a second component of very high gra de 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.