by Glenda Wright MBBCh and Allison Osmond MD FRCPC
March 9, 2023
Dermatofibrosarcoma protuberans (DFSP) is a type of skin cancer that starts just below the surface of the skin. DFSP can re-grow in the same location after surgery especially if the tumour was not completely removed during the first surgery. However, unlike other types of cancer, DFSP very rarely metastasizes (spreads) to other parts of the body.
DFSP is a type of sarcoma.
Most tumours start on the chest or back but any part of the body can be affected.
For most patients, the tumour is slow-growing and painless.
DFSP is caused by a genetic change that leads to the fusion (combination) of two genes COL1A1 and PDGFB. This genetic change results in increased production of the PDGFB protein and tumour development. Why some people develop this genetic change remains unknown.
Typical DFSPs almost never metastasize (spread) to other parts of the body. However, fibrosarcomatous DFSP is a more aggressive type of cancer that can metastasize.
The diagnosis is usually made after a small tissue sample is removed in a procedure called a biopsy. The diagnosis can also be made after the entire tumour is removed in a procedure called an excision. If the diagnosis is made after a biopsy, your doctor will probably recommend a second surgical procedure to remove the rest of the tumour.
Under the microscope, DFSP is made up of long thin cells called spindle cells that look very similar to the fibroblasts normally found in the dermis of the skin. The spindle cells grow in a circular pattern that pathologists call “spoke and wheel” or “cartwheel” pattern. The tumour starts in the dermis, but cancer cells are often found growing into the subcutaneous fat below. Your pathologist may perform a test called immunohistochemistry to help confirm the diagnosis. The tumour cells in DFSP are usually positive for CD34 and negative for Factor 13A.
Pathologists use the term fibrosarcomatous to describe a DFSP that has changed into a more aggressive tumour. Unlike the typical DFSP, fibrosarcomatous DFSP has the potential to metastasize (spread) to other parts of the body. When examined under the microscope, fibrosarcomatous DFSP may show a fascicular or herringbone pattern of growth. The tumour cells may also appear more atypical (abnormal looking in shape or size) and mitotic figures (tumour cells dividing to create new tumour cells) are frequently seen
A margin is any tissue that was cut by the surgeon in order to remove the tumour from your body. Whenever possible, surgeons will try to cut tissue outside of the tumour to reduce the risk that any tumour cells will be left behind after the tumour is removed. Your pathologist will carefully examine all the margins in your tissue sample to see how close the tumour cells are to the edge of the cut tissue. Margins will only be described in your report after the entire tumour has been removed.
DFSP has the potential to re-grow (recur), especially if it is not completely removed. The border between the tumour and the surrounding normal tissue can be difficult to see because the tumour cells in a DFSP often extend as small groups of cells at the edge of the tumour into the surrounding normal tissue. This can make removing the tumour challenging as your surgeon may not know exactly where the tumour ends.
A negative margin means there were no tumour cells at the very edge of the cut tissue. If all the margins are negative, most pathology reports will say how far the closest tumour cells were to a margin. The distance is usually described in millimetres. A margin is considered positive when there are tumour cells at the very edge of the cut tissue. A positive margin is associated with a higher risk that the tumour will recur in the same site after treatment.