The deep margin of fibrous histiocytomas usually shows limited infiltration into the subcutaneous tissues. This is in contrast to the more extensive infiltration seen in dermatofibrosarcoma protuberans (DFSP). DFSP has a more homogenous population of tumor cells and lacks inflammatory cells, foamy histiocytes, and giant cells. Storiform pattern is more pronounced in DFSP and mitotic activity is increased.
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