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.