MALIGNANT GIANT-CELL TUMOR OF THE TENDON SHEATHS AND JOINTS (MALIGNANT PIGMENTED VILLONODULAR SYNOVITIS)

Malignant pigmented villonodular synovitis (PVNS) is a rare lesion who se existence may be debatable. We studied eight cases that we consider to be examples of malignant PVNS. The three male and five female pati ents were aged 12 to 79 years. The knee was involved in three cases; t he ankle in two; and the cheek, dorsum of the foot, and thigh in one e ach. Four patients had swelling for 6 months to 17 years before presen tation. Three cases of malignant PVNS were secondary, arising in patie nts in whom PVNS had been documented previously, and five cases were p rimary, with histologic features similar to those of the secondary one s. Important histologic features of malignancy were (a) a nodular, sol id infiltrative pattern of the lesion, (b) large, plump, round or oval cells with deep eosinophilic cytoplasm and indistinct borders; (c) la rge nuclei with prominent nucleoli; and (d) necrotic areas. Atypical m itoses were occasionally seen. Four patients died with pulmonary metas tasis (two also had metastasis to inguinal lymph nodes). Four patients are alive from 3 1/2 to 5 years after the last surgical treatment. Th e malignant nature of this lesion, the histologic architecture similar to that of PVNS, and the fibrohistiocytic appearance of the cells sug gest that malignant PVNS is an entity.