Dermatofibrosarcoma Protuberans (DFSP): Understanding Your Pathology Report

by Jason Wasserman MD PhD FRCPC
April 24, 2026

Dermatofibrosarcoma protuberans (DFSP) is a rare type of skin cancer that starts in the dermis — the thick middle layer of the skin. It belongs to a broader family of cancers called sarcomas, which arise from connective tissue (the supportive framework that gives the skin and other organs their shape and strength). DFSP most often appears on the trunk, arms, or legs but can develop anywhere on the body.

Although DFSP is a cancer, it behaves differently from most other cancers. It grows slowly and very rarely spreads to lymph nodes or distant organs. Instead, its main concern is local — it grows in fine, finger-like extensions that can spread well beyond the visible edge of the tumor, making complete surgical removal challenging and local recurrence a real risk. This article will help you understand the findings in your pathology report for dermatofibrosarcoma protuberans — what each term means and why it matters for your care.

What causes dermatofibrosarcoma protuberans?

The exact cause of DFSP is not well understood. Unlike many skin cancers, DFSP is not linked to ultraviolet (UV) exposure. In almost all cases, the tumor develops due to a specific genetic change—a translocation between chromosomes 17 and 22 that creates an abnormal COL1A1-PDGFB fusion gene (discussed in more detail in the biomarker section below). This genetic change occurs in the cell during a person’s lifetime and is not inherited from a parent.

Some DFSPs develop in areas of skin that were previously injured — such as at the site of a scar, surgical wound, burn, vaccination, or tattoo — but most arise in skin without any history of injury. DFSP can occur at any age but is most commonly diagnosed in adults aged 20 to 50.

What are the symptoms of dermatofibrosarcoma protuberans?

The most common symptom of DFSP is a slow-growing lump on the skin. Common features include:

• A firm, rubbery skin lump — DFSP often begins as a flat, scar-like or bruise-like patch that may be red, brown, or skin-colored. Over time, one or more raised nodules (“protuberans” means protruding) develop within the patch.
• Slow growth — Most DFSPs grow over months to years, and some people notice the lesion for a long time before seeking medical attention.
• Usually painless — DFSP is typically not painful, though some people notice mild tenderness or itching.
• Skin changes — In advanced tumors, the skin over the lump may become thinned, ulcerated, or bleed easily.

Because DFSP is rare and its early appearance can resemble a bruise, scar, or harmless skin cyst, it is often mistaken for a benign condition, which can delay diagnosis.

How is the diagnosis made?

The diagnosis of DFSP is made after a tissue sample is examined under the microscope by a pathologist. The sample is obtained by a skin biopsy. Because DFSP grows deep within the dermis and into the underlying fat, a punch biopsy or small incisional biopsy is usually preferred over a superficial shave biopsy to allow the pathologist to see the deeper part of the tumor. Under the microscope, the pathologist identifies a tumor composed of long, narrow cells called spindle cells arranged in a swirling or cartwheel-like (storiform) pattern within the dermis. A thin layer of normal dermis, called a grenz zone, often separates the tumor from the epidermis. As DFSP grows, it typically extends into the fat beneath the skin in a lace-like or honeycomb pattern, with irregular finger-like extensions that reach beyond the visible edge of the tumor. Most DFSPs show very few dividing cells and only mild atypia, meaning the cells do not look markedly abnormal. The diagnosis is usually confirmed using a special test called immunohistochemistry, in which tumor cells show strong staining for the protein CD34. Imaging — such as ultrasound or MRI — is sometimes used to determine how deeply the tumor has grown into the underlying tissue and to help plan surgery.

Histologic subtypes

Several subtypes of DFSP have been described. All share the same underlying genetic change but differ in how the cells look under the microscope.

• Classic (conventional) DFSP — The most common form. Shows the typical storiform pattern of uniform spindle cells with strong CD34 staining.
• Giant cell fibroblastoma — A form that occurs most often in children. Shows large multinucleated giant cells arranged around blood vessel-like spaces.
• Myxoid DFSP — Contains large areas of jelly-like myxoid stroma. The swirling pattern is less obvious, which can make diagnosis more difficult.
• Pigmented DFSP (Bednar tumor) — Contains tumor cells with brown melanin pigment scattered among the spindle cells.
• Myoid DFSP — Shows nodules of pink spindle cells around blood vessels with hardened connective tissue. Unlike classic DFSP, it may lose CD34 staining and instead show staining for smooth muscle actin (SMA).
• Plaque-like DFSP — Grows in a flat, sheet-like pattern within the dermis. It can resemble other skin tumors and requires careful examination to confirm the diagnosis.

Fibrosarcomatous transformation

In about 10 to 15% of DFSPs, part of the tumor changes into a more aggressive form called fibrosarcomatous DFSP (sometimes reported as “DFSP with fibrosarcomatous transformation” or DFSP-FS). Under the microscope, these areas show more abnormal-looking cells, more frequently dividing cells (mitotic figures), and a herringbone growth pattern resembling another sarcoma called fibrosarcoma. CD34 staining is often reduced or lost in these areas.

Fibrosarcomatous transformation is important because it alters tumor behavior. Compared with conventional DFSP, fibrosarcomatous DFSP has a higher risk of local recurrence and carries a small but real risk (approximately 10 to 15%) of spreading to the lungs or other distant sites. For this reason, tumors with this change are treated more aggressively and followed more closely after treatment.

Margins

A margin is the edge of the tissue removed during surgery. Pathologists examine margins under the microscope to see whether any cancer cells are present at the cut edge. For DFSP, both the peripheral margin (the side edges of the removed tissue) and the deep margin (the bottom of the removed tissue) are evaluated.

• Negative margin — No cancer cells are seen at the cut edge. The tumor is considered completely excised, and the risk of recurrence is low.
• Close margin — Cancer cells are within a short distance of the cut edge but do not reach it. Because DFSP extends in fine finger-like projections that can be hard to see under the microscope, close margins may lead to recommendations for additional surgery.
• Positive margin — Cancer cells are present at the cut edge. Additional surgery is usually recommended to remove the remaining tumor.

Margins are especially important in DFSP because the tumor routinely extends well beyond what is visible to the naked eye. For this reason, wide local excision with a generous margin of healthy tissue — or Mohs micrographic surgery, a technique in which the tumor is removed in thin layers that are examined under the microscope during surgery — is used to ensure complete removal.

Biomarker and molecular testing

Molecular testing plays an important role in the diagnosis and treatment of DFSP. Testing is used to confirm the diagnosis in cases where the microscopic features are unusual, and to identify patients who may be candidates for targeted therapy if the tumor cannot be completely removed by surgery.

COL1A1-PDGFB gene fusion

More than 90% of DFSPs are caused by a specific genetic change called a translocation between chromosomes 17 and 22, written as t(17;22). This translocation joins part of the COL1A1 gene on chromosome 17 with part of the PDGFB gene on chromosome 22, creating an abnormal fusion gene called COL1A1-PDGFB. The fusion gene makes the tumor produce excess PDGFB protein, which continuously stimulates the cells to grow and divide.

Pathologists can detect this fusion using several techniques, including fluorescence in situ hybridization (FISH), reverse transcriptase polymerase chain reaction (RT-PCR), or next-generation sequencing (NGS). The result may be reported as the presence of a COL1A1-PDGFB gene fusion or a t(17;22) translocation. A small percentage of DFSPs are caused by alternative gene fusions involving PDGFD or other partners; these behave similarly to classic DFSP and are also detectable by NGS.

Imatinib for advanced DFSP

Because the COL1A1-PDGFB fusion drives DFSP by activating the PDGF receptor, DFSP is sensitive to a targeted drug called imatinib (Gleevec), which blocks this receptor. Imatinib is approved for adults with DFSP that cannot be cured by surgery — for example, because the tumor is too large or has spread to other organs. Response rates to imatinib in this setting are approximately 50 to 65%, with tumor shrinkage often making previously inoperable tumors suitable for surgery. Imatinib is not used as the first treatment for tumors that can be completely removed by surgery.

For more information about biomarkers and molecular testing in cancer, visit the Biomarkers and Genetic Testing section.

Is dermatofibrosarcoma protuberans staged?

DFSP is not assigned a formal pathologic stage in the way that most cancers are. The American Joint Committee on Cancer (AJCC) does not include DFSP in a dedicated TNM staging chapter because it so rarely spreads to lymph nodes or distant organs. When needed — for example, in the uncommon situation of fibrosarcomatous DFSP with metastatic spread — the TNM system used for soft tissue sarcomas of the trunk and extremities may be applied. For most patients with DFSP, the features that matter most for prognosis and treatment are the tumor size, depth of invasion, margin status, and whether fibrosarcomatous transformation is present.

What is the prognosis?

The overall prognosis for DFSP is excellent. When the tumor is completely removed with clear margins, long-term survival is near that of the general population, and distant spread is very uncommon. The main concern is local recurrence — the cancer coming back at the same site — which can usually be controlled with additional surgery.

Features associated with a higher risk of local recurrence or, rarely, distant spread include:

• Positive or close surgical margins — The most important factor in local recurrence, because DFSP extends in fine finger-like projections beyond the visible tumor.
• Fibrosarcomatous transformation — Associated with a higher rate of local recurrence and a small but real risk of distant spread.
• Large tumor size — Larger tumors are more difficult to remove completely.
• Deep invasion — Tumors that invade into underlying muscle, fascia, or bone are more difficult to remove.
• Recurrent tumor — A DFSP that has come back after previous treatment is more challenging to cure than a new tumor.
• Certain anatomic locations — Tumors on the head and neck are more difficult to remove with wide margins because of cosmetic and functional concerns.

For the small number of patients with advanced or metastatic DFSP (almost always with fibrosarcomatous transformation), the introduction of imatinib has substantially improved outcomes compared with the chemotherapy options that were available in the past.

What happens after the diagnosis?

Treatment of DFSP is usually coordinated by a team that may include a dermatologist, a surgical oncologist, a Mohs surgeon, and — for advanced disease — a medical oncologist and radiation oncologist.

For most DFSPs, surgery is the primary treatment. Two main surgical approaches are used:

• Wide local excision — The tumor is removed together with a generous margin of surrounding healthy tissue. This is the standard approach for DFSP on the trunk, arms, and legs.
• Mohs micrographic surgery — The tumor is removed in thin layers that are examined under the microscope during the operation to confirm that all cancer cells have been removed. Mohs is often preferred for DFSP on the head, neck, and other areas where preserving healthy tissue is important, and may also be used for recurrent tumors.

Radiation therapy is sometimes added after surgery when clear margins cannot be achieved (for example, when the tumor is too close to vital structures) or for tumors with fibrosarcomatous transformation. Radiation may also be used as the primary treatment in patients who are not candidates for surgery.

For locally advanced or metastatic DFSP that cannot be completely removed by surgery, the targeted drug imatinib (Gleevec) is the standard first systemic treatment. Imatinib can shrink the tumor enough to allow surgery in some cases. For patients whose tumors progress on imatinib, second-line options may include other tyrosine kinase inhibitors, enrollment in clinical trials, or, in the case of metastatic fibrosarcomatous DFSP, chemotherapy.

After treatment, regular follow-up with physical examination of the surgical site is important because DFSP can recur years after surgery. Imaging may be added for patients with fibrosarcomatous transformation or other high-risk features.

Questions to ask your doctor

• Where on my body did the DFSP develop, and how large was the tumor?
• What subtype of DFSP did I have?
• Was fibrosarcomatous transformation found in my tumor?
• How deeply did the tumor grow — was it confined to the skin, or did it involve the fat, muscle, or deeper tissue?
• Were the surgical margins negative, close, or positive? Do I need further surgery?
• Was molecular testing performed to confirm the COL1A1-PDGFB fusion?
• Would Mohs micrographic surgery be a better approach for my tumor?
• Do I need radiation therapy after surgery?
• Is systemic therapy such as imatinib appropriate for my case?
• How often should I be seen for follow-up, and for how long?
• Do I need imaging studies as part of my follow-up?
• What should I watch for that might suggest the tumor has come back?