Question:

A 35-year old man presented with a five-year history of an asymptomatic plaque on the right shoulder which had slowly increased in size. Nodules had appeared in the lesion in the past year. Some of these lesions had become confluent. There was no history of trauma and no significant past medical history.

Answer: B. Dermatofibrosarcoma protuberans

Dermatofibrosarcoma protuberans (DFSP) is an uncommon soft tissue sarcoma of intermediate malignancy. It affects males and females equally and has a high tendency of recurrence but is of low-metastatic potential. Patients are most commonly affected in the second to fifth decades, with the trunk and proximal extremities being the most common sites. The tumour may also occur in scars and sites of trauma. Typically, it presents as a slowly enlarging, indurated plaque which may be brown to dusky red in color in which nodules eventually appear. The initial lesion may also be flat or depressed. Later, there may be pain, rapid growth, discharge and ulceration. The diagnosis is often delayed and in the initial stages, the differential diagnoses include keloid, dermatofibroma, while in later lesions, DFSP has to be distinguished from morphoea.

Histolologically, in plaque stage DFSP, there are spindle-shaped cells forming horizontal fascicles that lie parallel to the skin surface. Little mitotic activity is seen at this stage. In the nodular phase, spindle shaped cells infiltrate normal collagen in the dermis, forming short fascicles which radiate like the spokes of a wheel (storiform pattern). Mitoses are frequent. Due to infiltration of the normal tissue by spindle cells at the edges of the lesion, there is often difficulty in defining the surgical margins.

Dermatofibrosarcoma protuberans is locally invasive, gradually enlarging both horizontally and vertically along the lines of least resistance. Muscle and bone may be affected due to deep extension. Treatment is by wide excision and as the lesion has indistinct clinical margins, recurrences are common. The rate of recurrence has been reported to be lower with Moh's surgery. Metastases are uncommon, the lungs, followed by the lymph nodes, are the most commonly affected sites.