Proliferative fasciitis mimicking a sarcoma in a child: a case report.

Proliferative fasciitis (PF) is a benign, discrete proliferation of fibroblasts or myofibroblasts in soft tissue. Proliferative fasciitis mostly occurs in adults and is often confused with a sarcoma because of its rapid growth and peculiar histological features. We report a case of PF mimicking a sarcoma which developed in a 13-year-old boy, who noticed a painful tumor, with gradual enlargement, in his right lower leg. Magnetic resonance imaging revealed that the tumor measured 34 mm × 20 mm × 41 mm and was located in the subcutaneous tissue. The tumor was surgically resected. Pathologically, the tumor was composed of a proliferation of atypical spindle cells, admixed with larger ganglion-like cells. Immunohistochemically, the tumor cells were positive for vimentin, cytokeratin, smooth muscle actin, HHF-35 and Fli-1. The tumor was subsequently diagnosed as a PF, although it was difficult to differentiate from a sarcoma. Five years after surgery, the postoperative course has been uneventful with no recurrence or metastasis.