The biopsy results indicated that the lesion was a dermatofibrosarcoma protuberans (DFSP)—a malignant fibrotic tumor of the skin and subcutaneous tissues. Note that the shiny surface and multilobular appearance can be characteristic of DFSP, but not all DFSPs present this way. Some may just present as a growing, firm, subcutaneous painful tumor.
DFSPs resemble a large irregular dermatofibroma, but a dermatofibroma is not a precursor to this. A DFSP is a separate malignant tumor, and not the result of a dermatofibroma that is growing out of control. While DFSPs typically do not metastasize, they can be locally aggressive, with a high recurrence rate after standard surgery. Because of this, the FP referred the patient to a Mohs surgeon to perform the excision. Mohs surgery allowed the surgeon to look at all margins of the lesion under a microscope to get the highest possible cure rate.
Two years later, this patient had no signs of regrowth. The most important lesson with this case was that one should not rely on incomplete biopsy sampling, especially when there is continued growth and symptoms that suggest an undiagnosed malignancy.
Photos and text for Photo Rounds Friday courtesy of Richard P. Usatine, MD. This case was adapted from: Smith M. Usatine R. Dermatofibroma. In: Usatine R, Smith M, Mayeaux EJ, et al, eds. Color Atlas of Family Medicine. 2nd ed. New York, NY: McGraw-Hill; 2013: 935-939.
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