Dermatofibrosarcoma Protuberans (DFSP)

Dermatofibrosarcoma protuberans is a rare low-grade cutaneous soft-tissue sarcoma arising in the dermis and subcutis, typically presenting as a slow-growing firm plaque or nodule, often skin-coloured or violaceous, on the trunk or proximal limbs of a middle-aged adult, frequently present for years and initially mistaken for a benign lesion before it becomes protuberant. Histologically it consists of monomorphic spindle cells in a storiform or cartwheel pattern that infiltrate the subcutaneous fat in a honeycomb manner, and it is characteristically CD34 positive, which helps distinguish it from a benign dermatofibroma, which is CD34 negative. Genetically it is driven by the translocation t(17;22), which forms the COL1A1-PDGFB fusion gene, causing constitutive platelet-derived growth factor B signalling and PDGF-receptor activation that drives proliferation, and this is the molecular target for imatinib. Its behaviour is low-grade but with a very high local recurrence rate, because it spreads with infiltrative finger-like projections beyond the visible margin; conventional DFSP rarely metastasises, but the fibrosarcomatous variant has a real metastatic potential of around eight to twenty-nine percent. Treatment is primarily surgical, with wide local excision with adequate margins or Mohs micrographic surgery to achieve clear margins, since margin control is the key to cure; radiotherapy is an adjunct for close or positive margins, and imatinib is used for unresectable, recurrent or metastatic disease and as neoadjuvant therapy to shrink large tumours.

DFSP recurs locally so often because, despite being low-grade, it does not grow as a well-circumscribed mass but infiltrates the surrounding dermis and subcutaneous fat with finger-like or tentacle-like projections that extend well beyond the clinically and even macroscopically apparent margin. If the surgeon excises only to the visible edge, microscopic tumour is left behind and the lesion recurs. This dictates the surgical strategy: the aim is to achieve clear margins, so I would perform a wide local excision with generous margins, or, where available, Mohs micrographic surgery, which examines the entire circumferential and deep margin intra-operatively and allows complete removal while sparing tissue, giving the best margin control and the lowest recurrence rate. Where margins are close or positive and re-excision is not possible, adjuvant radiotherapy is used. For large or unresectable tumours, neoadjuvant imatinib can shrink the tumour to make excision feasible, and imatinib is also used for recurrent or metastatic disease. Because recurrence can be late, these patients need long-term follow-up, and I would stage and follow the fibrosarcomatous variant more closely given its metastatic potential.