Skin -

Dermatofibrosarcoma protuberans (DFSP)

This article was last reviewed and updated on May 19, 2019
by Glenda Wright, MBBCh and Allison Osmond, MD FRCPC

Quick facts:

  • Dermatofibrosarcoma protuberans (DFSP) is a type of skin cancer.

  • Unlike most types of skin cancer, dermatofibrosarcoma starts below the surface of the skin and is made up of cells called fibroblasts and histiocytes.

 

Normal skin

Skin is the largest organ in your body. Normal skin is made up of different layers. The tissue at the very surface of the skin is called the epidermis. The tissue below the epidermis is called the dermis and it contains blood vessels and connective tissue. Below the dermis is a layer of fat called subcutaneous adipose tissue.

Many different types of cells are normally found in the dermis including fibroblasts and histiocytes. Fibroblasts produce the collagen and other substances that make the dermis strong. Histiocytes are a type of immune cell that protect the body from any infections or toxins that enter through the skin.

What is dermatofibrosarcoma protuberans?

Dermatofibrosarcoms (DFSP) is a type of skin cancer that starts in the dermis. For most patients, the tumour is slow growing and painless. Most tumours start on the chest or back but any part of the body can be affected.

How do pathologists make this diagnosis?

Under the microscope, dermatofibrosarcoma protuberans is made up of long thin cells called spindle cells that look very similar to the fibroblasts normally found in the dermis. 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 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, dermatofibrosarcoma protuberans very rarely travels to other parts of the body (metastasis).

Margins

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 cancer 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 cancer cells are to the edge of the cut tissue. Margins will only be described in your report after the entire tumour has been removed.

A margin is considered positive when there are cancer 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.

A negative margin means there were no cancer cells at the very edge of the cut tissue. If all the margins are negative, most pathology reports will say how far the closest cancer cells were to a margin. The distance is usually described in millimeters.

Dermatofibrosarcoma protuberans (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 cancer 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.

Why is this important? Cancer cells at the cut edge of the tissue (a positive margin) increases the risk that the tumour will grow back in the same location after treatment.

Immunohistochemistry

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

Molecular tests

Each cell in your body contains a set of instructions that tell the cell how to behave. These instructions are written in a language called DNA and the instructions are stored on 46 chromosomes in each cell. Because the instructions are very long, they are broken up into sections called genes and each gene tells the cell how to produce piece of the machine called a protein.

Sometimes, a piece of DNA falls off one chromosome and becomes attached to a different chromosome. This is called a translocation and it can result in the cell making a new and abnormal protein. If the new protein allows the cell to live longer than other cells or spread to other parts of the body, the cell can become a cancer (a malignant tumour).

Dermatofibrosarcoma protuberans sometimes contains a translocation that combines the gene COL1A1 translocation with 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 your tumor has been surgically removed. 

Why is this important? A translocation involving the COL1A1 or PDGFB genes confirms the diagnosis of dermatofibrosarcoma protuberans and excludes other types of tumours that can look similar under the microscope. 

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