ABSTRACT
Although giant cell tumour (GCT) is seen quite frequently, malignant giant cell tumour (MGCT) is a rare entity occurring in less than 1% of patients with GCT. It can develop as a primary (de novo) or a secondary form. Secondary malignant giant cell tumour occurs as a result of previous attempts at local control of a benign GCT i.e. post-surgical or post-irradiation. Malignant transformation has been very rarely reported in patients with GCT who have not received radiation treatment. We report a rare case of sarcomatous transformation in a benign giant cell tumour occurring six years after the primary surgery for GCT and without radiotherapy. This report of malignant spindle cell transformation of a conventional GCT of bone strengths the theory that there is a mesenchymal cell line in GCT which can spontaneously transform into sarcoma. The prognosis of such patients is poor because the malignancies are usually high grade sarcomas. Key Messages: Although giant cell tumour (GCT) is seen quite frequently, malignant giant cell tumour (MGCT) is a rare entity occurring in less than 1% of patients with GCT. It can develop as a primary (de novo) or a secondary form. The prognosis of such patients is poor because the malignancies are usually high grade sarcomas.