Higher magnification showing highly atypical cells some of which have spindle growth pattern. The tumor cells may be arranged in a storiform or fascicle pattern. Mitoses are abundant with some of the mitotic figures being atypical. Atypical fibroxanthomas can resemble melanoma, spindled squamous cell carcinoma, and sarcoma. Immunohistochemistry can be useful in such cases. Atypical fibroxanthomas will stain positive for vimentin, HAM56, and alpha1-antitrypsin, and they are negative for S-100, melan A, desmin and cytokeratins.