locally invasive tumor of joints and periarticular soft tissues composed of mononuclear fibroblastic cells, and hemosiderin-filled macrophages; mitoses are prominent and larger tumors show invasive growth and tendency to recur. These tumors are similar to localized giant cell tumor of soft tissues but are more cellular, show nuclear atypia, prominent nucleoli, and distinct chromosomal changes. Recurrence occurs in 30-50% cases; in rare cases they may be frankly malignant.
