Dermatofibrosarcoma Protuberans (DFSP)

01Clinically classic DFSP starts as a slowly enlarging asymptomatic skin-colored to pink, violaceous, or red-brown plaque, often initially mistaken for a scar, keloid, dermatofibroma, or morphea. Over years it develops one or more firm protuberant nodules within the plaque. Lesions in pigmented skin can show a brownish hue and reticulated pigment that mimics a melanocytic process. Diameter at diagnosis ranges from 1 to over 10 cm. Pediatric DFSP often presents as an atrophic plaque and is frequently misdiagnosed as morphea or vascular malformation, with diagnosis delays of 5 years or more reported.

02Dermoscopy of DFSP, especially in pigmented skin types, has been described in a multicenter case series (Bernard 2013) as a polymorphic combination of structureless light brown background, fine pigment network, vessels (linear-irregular, arborizing, or both), pinkish background, white shiny areas, and structureless hypopigmented areas. None of these is specific in isolation, but the combination of a pigment network, vessels, and structureless light brown areas in a slowly growing plaque on the trunk or shoulder is suggestive. Amelanotic and atrophic variants show pinkish background with vessels and white shiny structures, overlapping with scar and morphea.

03Histopathology shows monomorphic CD34-positive spindle cells in a tightly packed storiform (cartwheel) pattern infiltrating the dermis and subcutis, frequently extending along septa and into adipose tissue in finger-like projections (so-called honeycomb pattern). Mitoses are usually low (under 5 per 10 high-power fields) in classic DFSP. The diagnostic confirmation rests on diffuse strong CD34 positivity (with negative Factor XIIIa, which differentiates DFSP from cellular dermatofibroma) and detection of the COL1A1-PDGFB fusion or supernumerary ring chromosomes by FISH, RT-PCR, or RNA-seq.

04Approximately 10 to 15% of DFSPs harbor or evolve into a fibrosarcomatous (FS-DFSP) component, defined histologically by herringbone or fascicular architecture, increased mitotic activity, and often loss of CD34. FS-DFSP carries higher local recurrence (20 to 30%) and a metastatic risk in the 14 to 20% range (some pooled series report up to 30%), predominantly to lung. Other variants include pigmented (Bednar tumor), myxoid, atrophic, sclerosing, and granular cell, and giant cell fibroblastoma in children, all sharing the same COL1A1-PDGFB cytogenetic abnormality.

05Surgery is the cornerstone of treatment. Mohs micrographic surgery (or slow Mohs with paraffin-embedded sections) achieves local recurrence rates of 0 to 7% in pooled series, compared with 11 to 30% with wide local excision (WLE) at 2 to 5 cm margins. NCCN guidelines recommend complete circumferential peripheral and deep margin assessment (CCPDMA) such as Mohs as the preferred surgical approach, particularly on the head, neck, and other anatomically constrained sites.

06Imatinib mesylate, a tyrosine kinase inhibitor of PDGFR-beta and other targets, is FDA approved for unresectable, recurrent, or metastatic adult DFSP. Response rates of 50 to 75% are reported in fusion-positive disease at 400 to 800 mg daily; partial responses can be sustained for years. Imatinib is also used in the neoadjuvant setting to shrink large or anatomically challenging tumors before surgery, although duration and tolerability vary.

07Pediatric DFSP behaves similarly to the adult tumor genetically but is frequently underdiagnosed because of its atrophic or vascular-malformation-like clinical appearance. Treatment is the same (Mohs or wide excision), with imatinib reserved for unresectable disease in children for whom safety data exist. Long-term follow-up at 6- to 12-month intervals for at least 5 to 10 years is reasonable given the slow recurrence kinetics.

08Differential diagnosis is broad. The main pitfalls are atrophic morphea (no nodule, no fingerlike subclinical extensions, COL1A1-PDGFB negative), keloid (familial, in scar location, dermal collagen with no spindle cells), cellular dermatofibroma (smaller, factor XIIIa positive, CD34 negative or focal), neurofibroma (S100 positive), and superficial leiomyosarcoma (desmin and SMA positive).