[Extra-abdominal fibromatosis. An immunohistochemical analysis].

A 49-year-old patient presented with a slow-growing tumour on his back, which had been present for 10 years. Histologically an infiltrating spindle-cell tumour without cell polymorphism was found. Each cell was surrounded by collagen fibrils. Immunohistochemically the tumour cells showed positive staining with antibodies to alpha-smooth muscle actin, factor XIIIa, CD34 and vimentin. In contrast, antibodies to the intermediate filament protein desmin, glial fibrillary acid protein (GFAP), the neurofilament (NF), neuron-specific enolase (NSE), S-100 protein, carcinoembryonic antigen (CEA) and keratin protein (LU-5) revealed no staining of the spindle cells. This immunohistochemical profile supports myofibroblastic differentiation of the spindle cell in extra-abdominal fibromatosis.