<unk>  may resemble and therefore be misdiagnosed as dermatofibrosarcoma protuberans, fibrosarcoma, malignant fibrous histiocytoma, spindle-cell melanoma (a rare form of melanoma,) leiomyosarcoma, and inflammatory myofibroblastic tumor. The diagnosis of<unk>  and its variants depends on a combination of findings no single one of which is definitive. These findings are: the tumors': presentation (particularly its location in the cranium, within blood vessels, or outside of these areas); histopathology (particularly analyses of tumor cell mitoses which if atypical strongly suggest the tumor is not<unk> ; presence of myofibroblasts that typically express muscle-specific actin, SMA, and vimentin and may express CD68 but generally do not express S100, desmin, trypsin, factor VIII, F4/80, or CD34 (lack of Cd34-expressing cells indicates that the tumor is not a sarcoma); and presence of typical neoplastic cells expressing an USP6-containing fusion gene. (USP6-containing fusion genes also occur in the tumor cells of aneurysmal bone cysts, fibroma of tendon sheaths, giant cell reparative granuloma, and myositis ossificans/fibro-osseous pseudotumor of digits.) While virtually all cases of<unk>  and variants have had excellent prognoses, the two cases of individuals with an USP6-PPP6R3 fusion gene in their<unk>  tumor cells had less favorable prognoses: their tumors were locally invasive, repeatedly relapsed after surgical removal, and grew progressively larger over 2 and 10 years of observations.
Nodular fasciitis
Silicone granuloma
Pyogenic granuloma
Diffuse infantile fibromatosis
Acral necrosis
Aggressive fibromatosis
Juvenile hyaline fibromatosis
Villonodular synovitis