Dermatofibrosarcoma protuberans (DFSP)

by Glenda Wright MBBCh and Allison Osmond MD FRCPC
April 29, 2022


What is dermatofibrosarcoma protuberans?

Dermatofibrosarcoma protuberans (DFSP) is a type of skin cancer that starts in a part of the skin called the dermis. For most patients, the tumour is slow-growing and painless. DFSP can re-grow in the same location after surgery (local recurrence) 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.

Where is dermatofibrosarcoma protuberans normally typically found?

Most tumours start on the chest or back but any part of the body can be affected.

How do pathologists make the diagnosis of dermatofibrosarcoma protuberans?

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.

What does dermatofibrosarcoma protuberans look like under the microscope?

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.

dermatofibrosarcoma protuberans

The microscopic appearance of dermatofibrosarcoma protuberans (DFSP).

What other tests may be performed to confirm the diagnosis of dermatofibrosarcoma protuberans?

Immunohistochemistry

Your pathologist may perform a test called immunohistochemistry to help confirm the diagnosis. The tumour cells in DFSP are usually positive or reactive for CD34 and negative or non-reactive for Factor 13A.

Molecular tests

Dermatofibrosarcoma protuberans sometimes contains a type of genetic change called a translocation. The translocation in DFSP combines the gene COL1A1 translocation with the gene PDGFB. Pathologists test for this molecular change by performing either fluorescence in situ hybridization (FISH) or next-generation sequencing (NGS) on a piece of the tissue from the tumour. This type of testing is can be done on the biopsy specimen or when the tumour has been surgically removed. A translocation involving the COL1A1 or PDGFB genes confirms the diagnosis of DFSP and excludes other types of tumours that can look similar under the microscope.

What is a margin?

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.

Margin

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