Deep dermatofibrosarcoma protuberans: a subcutaneous variant.
AIMS: Dermatofibrosarcoma protuberans (DFSP) is a distinctive cutaneous spindle cell neoplasm that invariably infiltrates the subcutaneous tissue. Other reports have suggested that exceptional cases of DFSP may be confined to the subcutaneous tissue and lack dermal involvement. We wish to confirm this observation by describing cases of a rare variant of DFSP confined to the subcutaneous tissue, and analyse possible histogenetic implications. METHODS AND RESULTS: Three cases of DFSP located in the subcutaneous tissue are reported. Multiple step sections demonstrated the lack of dermal involvement in two of them, whereas the third case infiltrated the dermis at the junction with the subcutis minimally in one of five blocks. Immunohistochemical studies using a battery of monoclonal antibodies were performed. All the tumours stained strongly for vimentin and CD34. CONCLUSIONS: Because of the lack of dermal involvement in two cases and only minimal dermal involvement in one case, we called this variant deep DFSP. Except for deep setting of the tumour, deep DFSP is indistinguishable from typical DFSP clinically, histologically and immunohistochemically. The existence of deep DFSP provides evidence that specific structures of the skin may be not involved in this tumour's histogenesis.