Dermatofibrosarcoma Protuberans (DFSP)

DFSP is rare - of the order of a few cases per million people per year - and accounts for roughly one in a hundred soft-tissue sarcomas, but it is the commonest sarcoma to arise primarily in the skin. It presents most often between the third and fifth decades, in adults of any sex, and has a recognised predilection for darker skin, in whom the pigmented variant is over-represented. Site distribution matters because it predicts the reconstructive problem: roughly half arise on the trunk, about a third on the proximal limbs, and the remainder on the head and neck, where tissue is scarce and margin-sparing technique becomes decisive. A minority arise at sites of previous trauma, burns, scars or vaccination, which is one reason a "scar" that thickens, spreads laterally or becomes nodular after years of stability deserves biopsy rather than reassurance.

The natural history explains the classic late presentation. The tumour begins as a firm, indurated plaque that enlarges over years - often described by the patient as a bruise or a scar that never settled - before entering the protuberant phase, in which one or more nodules rise from the plaque and growth accelerates. Median symptom duration before diagnosis is measured in years, and the lesion is frequently excised marginally as a presumed cyst or dermatofibroma before the diagnosis is made. Such an unplanned excision does not change the biology, but it does convert a straightforward wide excision into a re-excision of a contaminated field: the whole previous scar and any drain sites must be taken with the specimen. Our Soft-Tissue Masses & Sarcoma Referral topic covers that referral pathway in full.

Variants worth naming

• Fibrosarcomatous DFSP (FS-DFSP) - transformation to a higher-grade tumour, arising either at presentation or in a recurrence. The storiform pattern gives way to fascicular, herringbone architecture with markedly higher mitotic activity and, importantly, loss of CD34 staining in the transformed areas. It is the one variant with real metastatic potential and the one that changes staging and follow-up.
• Pigmented DFSP (Bednar tumour) - conventional DFSP containing scattered melanin-laden dendritic cells, giving the lesion a brown or blue-black hue that can suggest melanoma clinically. Behaviour is that of conventional DFSP; the pigment is not adverse.
• Giant cell fibroblastoma - the juvenile counterpart, carrying the same COL1A1-PDGFB fusion, with pseudovascular spaces lined by multinucleate giant cells. It can recur as conventional DFSP and DFSP can recur as giant cell fibroblastoma, which is why the two are regarded as one entity across the age spectrum.
• Myxoid and sclerosing areas are common focally and matter mainly because they can mislead a small biopsy away from the diagnosis.

What the margin buys, and what follows it

The reported difference between techniques is the number to have ready. Series of conventional wide local excision report local recurrence in the region of five to twenty per cent, the spread reflecting how wide the margin was and whether the deep fascia was taken; Mohs or staged CCPDMA excision, which examines the whole margin rather than sampled sections of it, reports recurrence in low single figures. That is the argument for complete margin assessment, and it is strongest exactly where wide margins are unaffordable - the face, scalp, hands and feet. Where neither is available, the fallback is a generous excision with careful orientation of the specimen and a low threshold for re-excision rather than acceptance of a close margin.

Recurrence is overwhelmingly local and most often declares itself within the first three years, so surveillance is clinical: inspection and palpation of the scar and the surrounding skin, roughly six-monthly for the first few years and then annually, continued long-term because late recurrence beyond five years is described. Routine imaging of the primary site is not required after a clear margin; cross-sectional imaging is reserved for a suspicious clinical finding. Fibrosarcomatous disease is the exception that earns interval chest imaging alongside clinical review.

Where imatinib is used, it is given as a continuous daily tyrosine-kinase inhibitor in the neoadjuvant, unresectable or metastatic setting, and it is a cytoreductive agent rather than a curative one - responses are common but partial, so the plan should be to convert an unresectable tumour into a resectable one and then operate, not to substitute drug for surgery. Two practical caveats follow from that: confirm the fusion before committing, since fusion-negative tumours are not expected to respond, and time the operation to the response plateau rather than continuing indefinitely.