Dermatofibrosarcoma protuberance with a unique appearance mimicking neurofibroma arising from a conventional area.

A 21 year-old Japanese man had a rapidly growing pedunculated soft tumor in the abdomen within the past year, the base of which had persisted for 17 years. A skin biopsy of the soft part resembled neurofibroma. However, the excised specimen showed that the tumor base comprised spindle cells arranged in a storiform fashion and expanded around fat cells with a honeycomb infiltration. All areas of the tumor were positive for CD34 and negative for S-100. Finally, the tumor was diagnosed as a myxoid dermatofibrosarcoma protuberance arising from a conventional area. The pedunculated shape on the conventional part was unique. Myxoid dermatofibrosarcoma protuberances may pose a diagnostic challenge, particularly with a small biopsy. Thus, we should carefully consider dermatofibrosarcoma protuberances or other malignant mesenchymal tumors as a differential diagnosis in cases of low cellularity and abundant stromal tumors resembling neurofibromas.