Dermatofibrosarcoma protuberans (DFSP) is a rare tumor that affects the deep layers of the skin. It begins as a rough, reddish or purple patch of skin. This slowly enlarges and may form a small raised nodule. At this time, it may look reddish and may begin to bleed, or become tender. Local spread is common and multiple raised growths may occur in the vicinity of the first.
The most common site of DFSP is over the torso, arms, legs, head and neck. The tumor affects women slightly more often than men, and is most frequently observed to occur between the ages of 20 and 50 years.
Local recurrence is extremely common following excision, but metastasis is rare. However, tentacle-like extensions may be observed to occur into the neighboring tissues of the skin or underlying bone.
How DFSP Occurs
DFSP is the result of a mutation in one of the cells that make up the body, which then proliferates to produce a tumor. It is not inherited, but occurs as a sporadic translocation between chromosomes 17 and 22 (t:17;22).
The specific genes involved are the COL1A1 on the 17th chromosome with the PDGFB gene on the 22nd chromosome, and the translocated material forms an extra chromosome. This is either linear or circular in shape.
The latter are termed supernumerary ring chromosomes. These are formed by the fusion of the sticky ends of the arms of any chromosome which suffers a DNA break in two places. These ring chromosomes occur only in the affected cells, that is, within the tumor. Thus, it represents a somatic mutation.
The COL1A1 Gene
The COL1A1 gene is responsible for the manufacture of a large protein molecule involved intimately in the structural framework and support of most organs and tissues in the body. This important molecule is called collagen type 1.
The PDGFB Gene
The PDGFB gene encodes the protein, which is called platelet-derived growth factor, in one of its several isoforms. This protein binds to a specific receptor and activates many crucial cellular processes, such as cell growth, cell proliferation, and cell differentiation, by which it becomes mature.
The COL1A1-PDGFB Ring Chromosome
The abnormal circular piece of genetic material formed by the fusion of these two genes (in part) encodes the translation of an abnormal or fusion protein, which has functions similar to the PDGFB protein, but is produced in massive excess. This leads to the hyperstimulation of proliferative processes relating to the involved cells, causing tumor production.
This gene is present in more than 9 out of every 10 patients with DFSP. In other patients, other genetic alterations may be present, though not identified as of yet. It is noteworthy that these tumors grow much faster when they occur during pregnancy.