Dermatofibrosarcoma Protuberans
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Direct answer
Dermatofibrosarcoma protuberans is a low-grade, locally aggressive dermal sarcoma of fibroblast-like cells that grows slowly as a firm, indurated plaque or nodule, most often on the trunk. Its storiform, cartwheel pattern and diffuse CD34 positivity support the diagnosis, and a t(17;22) translocation creates a COL1A1-PDGFB fusion. Wide excision with clear margins is the standard treatment, because local recurrence follows incomplete removal.
What you must remember
- Behaviour: locally aggressive and low to intermediate grade, with metastasis being rare, though recurrence after incomplete excision is common.
- Age and site: young and middle-aged adults; the trunk is the commonest site, followed by the proximal limbs.
- Clinical look: a slowly enlarging, firm, skin-coloured or reddish-purple plaque, sometimes with nodules; the pigmented variant is called the Bednar tumour.
- Histology: a dense dermal proliferation of spindle cells in a storiform, cartwheel pattern, infiltrating subcutaneous fat in a honeycomb manner.
- Immunohistochemistry: CD34 is diffusely positive, while factor XIIIa and S100 are usually negative.
- Genetics: a t(17;22)(q22;q13) translocation forms a COL1A1-PDGFB fusion, which activates PDGF signalling; ring chromosomes are also seen.
- Treatment: wide local excision with clear margins, commonly quoted as 2 to 3 cm laterally and down to fascia; Mohs surgery for recurrence or sensitive sites, and imatinib for unresectable or metastatic disease.
From a slow plaque to a clear-margined excision
A firm, slowly growing plaque on the trunk of a young adult should not be dismissed as a scar or keloid. The steps below show how the diagnosis is reached and how treatment is planned.
- Recognise the lesion: a slowly enlarging, firm plaque that is often mistaken for a scar, keloid or dermatofibroma.
- Biopsy deeply: an incisional or punch biopsy that reaches subcutaneous fat, because superficial samples can miss the storiform pattern.
- Confirm with CD34: diffuse CD34 positivity with factor XIIIa negativity separates DFSP from dermatofibroma.
- Test for the fusion if needed: FISH or RT-PCR for the COL1A1-PDGFB fusion settles equivocal cases.
- Plan the excision: wide local excision with clear margins, taking the tumour down to fascia, is the standard operation.
- Use Mohs for recurrence: micrographic surgery checks margins in real time and spares tissue, which matters on the face.
- Consider imatinib: reserved for unresectable, recurrent or metastatic disease, where PDGF signalling is the target.
Where the exam tries to catch you
Dermatofibrosarcoma protuberans is easy to dismiss as a benign lesion because it looks like a plaque or scar.
- Trap: calling it a dermatofibroma because of the firm, flat plaque. Correct: dermatofibroma is CD34 negative and factor XIIIa positive, whereas DFSP is CD34 positive with a sarcomatous infiltrate into fat.
- Trap: planning a shave or a narrow margin to save tissue. Correct: recurrence after incomplete excision is common, so margins must be cleared, with Mohs preferred when needed.
- Trap: choosing radiotherapy as first-line treatment. Correct: surgery is the first-line option, and radiotherapy is reserved for disease that cannot be fully resected.
- Trap: expecting systemic spread to drive management. Correct: metastasis is rare, so local control, not systemic staging, is the priority.
Frequently asked questions
Which immunohistochemical marker helps diagnose dermatofibrosarcoma protuberans?
CD34 is strongly and diffusely positive in dermatofibrosarcoma protuberans, while factor XIIIa is usually negative. This pattern helps separate it from dermatofibroma, which is typically CD34 negative and factor XIIIa positive.
What is the genetic abnormality in dermatofibrosarcoma protuberans?
Dermatofibrosarcoma protuberans typically carries a t(17;22)(q22;q13) translocation that creates a COL1A1-PDGFB fusion gene. The fusion drives PDGF signalling, and the same pathway explains the response to imatinib in unresectable disease.
Why is Mohs surgery preferred for dermatofibrosarcoma protuberans?
Mohs micrographic surgery checks the margins in real time and removes tumour with tissue sparing, which suits cosmetically sensitive sites such as the face. It is also favoured after recurrence, because clear margins are the main determinant of local control.
Does dermatofibrosarcoma protuberans commonly metastasise?
Metastasis is rare in dermatofibrosarcoma protuberans, which is low-grade and locally aggressive. Management therefore focuses on clear local margins, and recurrence after incomplete excision is the main clinical problem.
Which drug treats unresectable dermatofibrosarcoma protuberans?
Imatinib is used for unresectable, recurrent or metastatic dermatofibrosarcoma protuberans, because the PDGFB fusion activates PDGF receptor signalling. Responses are variable, so it is usually given in specialist centres when surgery cannot clear the disease.