Author: Dr Harriet Cheng, Dermatology Registrar, Waikato Hospital, Hamilton, New Zealand, 2013.
Dermatofibrosarcoma protuberans (DFSP) is a locally aggressive tumour of fibloblastic origin. The initial lesion is a skin-coloured plaque which develops a red/brown colour and nodular surface.
Dermatofibrosarcoma protuberans consists of a proliferation of spindle shaped cells in the deep dermis with later lesions infiltrating the subcutaneous fat (Figures 1, 2). Invasion of muscle may occur. There is often superficial sparing, however involvement of the epidermis and ulceration is sometimes seen. Spindled tumour cells are quite uniform in appearance with elongated nuclei and little or no pleomorphism (Figures 3-5) and may be arranged in a storiform manner (swirled and interwoven, figure 6).
Characteristic positivity for CD34 (Figure 7). Negative CD31 and smooth muscle actin.
Cellular dermatofibroma: Radial proliferation of cells with large nuclei. May have haemodsiderin deposits. Central part negative for CD34, positive for Factor XIIIa.
Dermal sarcoma: Marked nuclear polymorphism and frequent mitoses are differentiating features from dermatofibrosarcoma protuberans.
Leiomyosarcoma: Pleomorphic spindle cell tumour with cigar-shaped nuclei and mitoses. Smooth muscle actin positive.
Desmoplastic melanoma: Fibrosis and focal lymphocytic infiltrates are additional features. Tumour cells are S100 positive.
Neurofibroma: S100 positive spindle cell tumour. Mast cells may be present.
Fibrosarcomatous dermatofibrosarcoma protuberans: Variant of dermatofibrosarcoma protuberans representing tumour progression. A focal fascicular or “herring-bone” pattern is present. More cellular with increased nuclear pleomorphism and mitotic figure count. Staining for CD34 reduced.
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