Malignancy in giant cell tumor of bone

BACKGROUND: The term malignant giant cell tumor embraces multiple entities and therefore can be confusing. The goals of the current study were to define the clinicopathologic and histologic features of malignancy in giant cell tumors and to clarify the terminology. METHODS: The authors reviewed all cases from the Rizzoli Institute (Bologna, Italy) of primary (PMGCT) and secondary (SMGCT) malignancy in giant cell tumors. PMGCT is a high-grade sarcoma that arises side by side with benign giant cell tumors. SMGCT is a high-grade sarcoma that occurs at the sites of previously treated giant cell tumors of bone. RESULTS: The authors report 5 PMGCTs and 12 SMGCTs; half of the SMGCTs were postradiation sarcomas. Patient age ranged from 20 to 68 years (median, 62 years) for PMGCT and from 30 to 77 years (median, 40 years) for SMGCT. The average latent period between diagnosis of giant cell tumor and diagnosis of SMGCT was 9 years (range, 3-15 years) for patients with postradiation SMGCT and 19 years (range, 7-28 years) for patients with SMGCT resulting from spontaneous transformation. The histologic classification of high-grade sarcomas in the PMGCT group was osteosarcoma in four cases and malignant fibrous histiocytoma in one case. In the SMGCT group, the histologic classification was osteosarcoma in nine cases, fibrosarcoma in two cases, and malignant fibrous histiocytoma in one case. The outcomes associated with all malignancies in giant cell tumors were poor, with the worst outcome associated with postradiation SMGCT. CONCLUSIONS: Malignancies in giant cell tumors of bone always are high-grade sarcomas with a poor prognosis. These lesions must be distinguished from benign giant cell tumors of bone. SMGCT usually is easy to diagnose upon malignant clinicoradiographic presentation. In contrast, PMGCT often mimics giant cell tumors both clinically and radiographically. In addition, upon histologic examination, PMGCT shows areas of conventional giant cell tumor, which can lead to difficulties in making the correct diagnosis.