Malignant giant cell tumor of the tendon sheaths and joints (malignant pigmented villonodular synovitis).

Malignant pigmented villonodular synovitis (PVNS) is a rare lesion whose existence may be debatable. We studied eight cases that we consider to be examples of malignant PVNS. The three male and five female patients were aged 12 to 79 years. The knee was involved in three cases; the ankle in two; and the cheek, dorsum of the foot, and thigh in one each. Four patients had swelling for 6 months to 17 years before presentation. Three cases of malignant PVNS were secondary, arising in patients in whom PVNS had been documented previously, and five cases were primary, with histologic features similar to those of the secondary ones. Important histologic features of malignancy were (a) a nodular, solid infiltrative pattern of the lesion; (b) large, plump, round or oval cells with deep eosino philic cytoplasm and indistinct borders; (c) large nuclei with prominent nucleoli; and (d) necrotic areas. Atypical mitoses were occasionally seen. Four patients died with pulmonary metastasis (two also had metastasis to inguinal lymph nodes). Four patients are alive from 3 1/2 to 5 years after the last surgical treatment. The malignant nature of this lesion, the histologic architecture similar to that of PVNS, and the fibrohistiocytic appearance of the cells suggest that malignant PVNS is an entity.