It rarely occurs above the neck. Currently, the cause of DFSP is unknown. Skin biopsy is essential for definite diagnosis. No imaging studies are employed unless metastatic disease is suspected after thorough history taking and physical examination. In the plaque type of DFSP, slender tumor cells with large, spindle-shaped nuclei are embedded fairly uniformly in the collagen stroma, parallel to the skin surface.
Mitotic figures are sparse.
The more characteristic findings are seen in the nodular type. These include the high cellularity and irregular short intersecting bands of tumor cells forming a storiform pattern. Also typical are cells radiating from a central hub of fibrous tissue forming a cartwheel pattern. The degree of cellular atypia is higher in nodular than in plaque lesions. Occasionally, DFSP may show focal fibrosarcomatous changes with a characteristic herringbone pattern.