Malignancy in pigmented villonodular synovitis.

Malignant pigmented villonodular synovitis is an extremely rare and controversial disease. We describe malignant change in pigmented villonodular synovitis of the ankle in a patient with an unusually long clinical history. Symptoms began at age 21, metastatic disease developed at age 85, and the patient died 1 year later. The histologic appearance of the malignant tumor differed from that in most reported cases, in that spindle-shaped cells predominated. Lymph node metastasis also developed, a feature uncommon to soft tissue sarcomas.