Malignancy, aggressiveness, and recurrence in giant cell tumor of bone

Eighty-six cases of giant cell bone tumor were reviewed with particular attention to frank sarcomatous changes, abnormal mitoses, permeation of vascular channels, and the number of mitoses per square millimeter, and the results were analyzed in relation to malignancy, aggressiveness, and recurrence. There were 4 cases of malignant (Grade III) tumor (about 5%) showing frank sarcomatous changes. Eight (9%) were considered cases of borderline (Grade II+) tumor, without frank sarcomatous changes but showing abnormal mitoses or vascular permeation. Seventy-four (86%) were cases of conventional giant cell tumor (Grades I and II). Mitotic counts did not categorically distinguish the three groups because of overlap. Recurrence essentially reflected the inadequacy of treatment. Metastases were observed only in the malignant group. About a quarter of conventional giant cell tumors were considered aggressive on clinical or radiologic grounds, but these could not be identified on a histologic basis. Tumors with minimal mitotic activity (1/mm2 or less) were almost exclusively nonaggressive. Post-irradiation sarcomas, best regarded as independent new tumors, developed in 4 cases (about 5%).