Dermatofibrosarcoma protuberans (DFSP) is a rare skin tumor arising in the dermal layer of skin. It occurs in about 1 in 100,000 to 10 million. It may occur at any age, but it is most common in the age group of 20-50 years.
It may initially appear deceptively benign, like a pimple or a roughened area of the skin, without redness or inflammation. No changes may be observed for months or years thereafter, but eventually enlargement occurs. The tumor is locally invasive and has a tendency to recur, because of the presence of tentacles, which spread invisibly into the surrounding skin, muscle and even underlying bone. However, only about 5 percent of cases show metastasis.
The tumor is typically diagnosed late, because of the lack of symptoms other than a patch of somewhat abnormal skin. In newborns, it may be mistaken for hemangiomas or other birthmarks. It may also pass for a pimple or scar.
The limited symptomatology associated with DFSP means that diagnosis is often made late, often after significant enlargement has occurred. The morphological overlap with other conditions means that skin biopsy is needed to confirm the diagnosis.
The histology of the tumor is that of a spindle cell tumor, which was first observed in 1924 by Darier and Ferrand. It arises within the cutaneous dermal layer and forms a multilobulated mass. Almost imperceptible strands extend from the tumor outwards to form tentacles. The failure to remove these tentacles during excision is a risk factor for local recurrence in many cases. The tumor may involve subcutaneous tissue, local muscular tissue and skeletal tissue as well if left undisturbed.
The microscopic appearance shows densely arranged spindle cells, uniformly arranged within fibrous stromal tissue. They may show infiltration into the fatty tissue around them. The nuclei show low to moderate number of mitoses, which corresponds with the low aggressive nature of the tumor. Areas of myxoid or collagenous predominance may occur, as well as hemorrhagic spots. The local extensions are not always easy to evaluate by microscopy.
The skin biopsy helps to confirm the diagnosis of DFSP and also to grade the tumor based on its histologic appearance and invasiveness.
There are different types of DFSP, including:
- Bednar tumors or pigmented DFSP that have pigmented melanin-rich dendritic cells
- Myxoid DFSP that have myxoid stroma
- Giant cell fibroblastoma or juvenile DFSP, which affects children and adolescents, and contains giant cells
- Fibrosarcomatous DFSP (FS-DFSP), which contain sarcomatous change of a more aggressive sort and are at a higher risk for metastasis, and therefore need to be treated more aggressively
The characteristic supernumerary ring chromosome formed by the reciprocal translocation of the 17th and 22nd chromosomes can be detected in over 90% of patients with DFSP. This is mostly detected using reverse transcription polymerase chain reaction (RT-PCR) or fluorescence in situ hybridization (FISH) technology.
Imaging techniques are increasingly used in the diagnosis of DFSP, especially if there is any suspicion of metastatic tumor, or in order to rule out the presence of fibrosarcomatous transformation. This may involve ultrasound visualization of the lymph nodes and of the abdominopelvic area, X-rays of the chest to rule out pulmonary metastasis, and computerized tomography (CT) scanning. Other imaging modalities may be used as required.