Giant cell fibroblastoma. A case report.

A case of giant cell fibroblastoma occurring in the knee of a 16-month-old girl is reported. The ill-defined subcutaneous tumor measuring 2 x 2 cm was composed of diffusely proliferating spindle-shaped tumor cells with scattered, atypical multinucleated giant cells in a myxoid or collagenous background and irregularly branching sinusoid-like tissue spaces. In addition to floret-type giant cells, a few osteoclast-like giant cells were present in a cellular area where tumor cells were focally arranged in a storiform pattern. Immunohistochemically, the tumor cells gave positive reactions for only vimentin and actin. In spite of the high recurrence rate of this type of tumor, the course of the patient after excision of the tumor has been uneventful. It is important to distinguish this rare, peculiar fibrous tumor from other soft tissue tumors including some sarcomas.