Your pathology report for dermatofibrosarcoma protuberans (DFSP)

by Jason Wasserman MD PhD FRCPC
September 15, 2025

Dermatofibrosarcoma protuberans (DFSP) is a rare type of skin cancer that starts in the connective tissue. Connective tissue is the supportive framework that gives the skin its structure and strength. DFSP often grows slowly and usually appears as a firm bump on the skin. It most often develops on the trunk, arms, or legs, but can occur anywhere on the body. While DFSP rarely spreads to other parts of the body, it can grow deeply into nearby tissues if left untreated.

What are the symptoms of dermatofibrosarcoma protuberans?

The most common symptom of DFSP is a skin lump. In its early stages, the lump may look like a bruise or scar and feel smooth or rubbery. Over time, it may increase in size and become raised above the skin surface. Some tumors may develop into multiple nodules or a large, bumpy mass. DFSP is usually not painful, but some people may notice itching, tenderness, or changes in the appearance of the skin over the lump.

What causes dermatofibrosarcoma protuberans?

The exact cause of DFSP is not fully understood. In most cases, it is associated with a specific genetic change within the tumor cells. These changes are not inherited from parents but develop during a person’s lifetime. In some cases, DFSP may develop in an area of skin that was previously injured, although this is not always the case.

Is dermatofibrosarcoma protuberans benign or malignant?

DFSP is a malignant tumor, which means it is a type of cancer. Malignant tumors can invade and damage surrounding tissues. However, DFSP is less aggressive than many other cancers because it rarely metastasizes (spreads) to distant organs. The primary concern with DFSP is its ability to regrow if not completely removed.

How is this diagnosis made?

The diagnosis of DFSP usually begins with a physical exam followed by a biopsy. A biopsy is a procedure where a small piece of the lump is removed and examined under a microscope by a pathologist. Pathologists look for the characteristic features of DFSP. In some cases, additional tests are performed to confirm the diagnosis.

Microscopic features of dermatofibrosarcoma protuberans

Under the microscope, DFSP is composed of long, narrow cells known as spindle cells. These cells are uniform in size and often arranged in a swirling or cartwheel-like (storiform) pattern. The tumor usually grows in the dermis, the thick middle layer of the skin, and is separated from the top layer (the epidermis) by a clear space called a grenz zone.

As DFSP grows, it frequently extends into the fat beneath the skin in a lace-like or honeycomb pattern. The edges of the tumor are often poorly defined and may spread in a tentacle-like fashion. Most tumors show very few dividing cells and only minimal atypia, meaning the cells look close to normal.

Histologic subtypes of dermatofibrosarcoma protuberans

Several subtypes of DFSP have been described. Each has unique microscopic features but shares the same underlying biology.

• Giant cell fibroblastoma is most often seen in children and shows large multinucleated giant cells, usually arranged around blood vessel-like spaces.
• Myxoid DFSP contains large areas of jelly-like material called myxoid stroma. The typical swirling pattern is less obvious, which can make diagnosis more difficult.
• Pigmented DFSP contains tumor cells with melanin pigment. These pigmented cells can be identified with special stains, such as S100.
• Myoid DFSP shows nodules of pink spindle cells around blood vessels, often with hardened tissue (stromal hyalinization). Unlike classic DFSP, it may lose CD34 staining and instead show staining for SMA, a marker of muscle-like cells.
• Plaque-like DFSP grows in a flat, sheet-like pattern in the dermis. It may resemble other skin tumors and requires careful examination to confirm the diagnosis.

What other tests may be performed to confirm the diagnosis?

Pathologists often use a technique called immunohistochemistry (IHC) to help confirm the diagnosis of DFSP. Immunohistochemistry uses antibodies linked to colored markers to detect specific proteins in tumor cells. This allows pathologists to see which proteins are being made by the tumor.

A key feature of DFSP is strong staining for a protein called CD34. This helps distinguish DFSP from other tumors that may look similar under the microscope. In some subtypes or tumors with fibrosarcomatous transformation, CD34 staining may be reduced or absent, providing valuable diagnostic information. Additional markers, such as SMA or S100, may be used depending on the tumor subtype.

Molecular tests

Most DFSP tumors are caused by a genetic change called a translocation. A translocation happens when pieces of two different chromosomes break and switch places. In DFSP, the translocation involves chromosomes 17 and 22, resulting in the creation of a fusion gene called COL1A1-PDGFB. This gene produces too much of a protein that stimulates tumor growth.

Pathologists can look for this genetic change using specialized molecular tests. Common methods include fluorescence in situ hybridization (FISH), reverse transcriptase polymerase chain reaction (RT-PCR), or next-generation sequencing (NGS). The result may be described in the pathology report as the presence of a COL1A1-PDGFB gene fusion or a t(17;22) translocation. Detecting this abnormality helps confirm the diagnosis of DFSP and, in some cases, may also guide targeted therapy.

Fibrosarcomatous transformation

In about 10% of cases, DFSP develops areas that look and behave more aggressively. This is called fibrosarcomatous transformation. Under the microscope, these areas exhibit more abnormal-looking cells, higher rates of cell division, and a growth pattern resembling that of fibrosarcoma. They may also lose CD34 staining.

Fibrosarcomatous transformation is important because it is associated with a higher risk of recurrence and, in some cases, metastasis. For this reason, tumors with this change are typically treated more aggressively and closely monitored.

Margins

When DFSP is surgically removed, the pathologist examines the edges of the specimen, known as the margins, to determine if any tumor cells are present.

• Negative (clear) margins indicate that no tumor cells are visible at the edges, suggesting the tumor was removed entirely.

• Positive margins mean tumor cells are present at the edge, which increases the risk of recurrence.

Margins are especially important in DFSP because the tumor often extends beyond what is visible to the naked eye. Wide local excision or Mohs micrographic surgery is usually recommended to ensure complete removal.

What is the prognosis for someone diagnosed with dermatofibrosarcoma protuberans?

The overall prognosis for DFSP is excellent. Surgery is the primary treatment and is usually curative when the tumor is completely removed. Mohs micrographic surgery is often used to minimize recurrence while preserving as much healthy skin as possible.

Although DFSP rarely spreads to other parts of the body, it can return if any tumor cells are left behind. Due to this, regular follow-up is crucial. With proper treatment, most people with DFSP have an excellent long-term outcome.

Questions for your doctor

If you have been diagnosed with dermatofibrosarcoma protuberans, you may wish to ask your doctor the following questions:

• Was the tumor completely removed, and were the margins clear?

• Did the pathologist perform immunohistochemistry or molecular testing, and what were the results?

• Was there any evidence of fibrosarcomatous transformation in my tumor?

• What kind of follow-up care do I need to monitor for recurrence?

• Would Mohs micrographic surgery or other specialized treatments be appropriate for my case?