Dermatofibrosarcoma Protuberans: Is Mohs Surgery Truly Superior? And the Success of Tyrosine Kinase Inhibitors

Dermatofibrosarcoma protuberans (DFSP) is rare tumor. DFSP only represents 1-2% of all soft tissue sarcomas.¹ The overall incidence of DFSP ranges from 0.8 per million to 5 per million. The Surveillance, Epidemiology, and End Results (SEER) Program, overseen by the National Cancer Institute, reports 4.2 per million. This tumor can take months to years to grow. As a result, definitive diagnosis is usually delayed. The tumor is usually freely mobile, although some may be found adherent to the underlying periosteum or fascia. In this review, we summarize the salient features of this condition and outline novel treatment approaches, including medical therapy with tyrosine kinase inhibition.

DFSP occurs most frequently at the age ranges of 20 to 50. The most common area on which DFSP originates is the trunk (50- 60%), followed by proximal extremities (20-30%), and the head and neck (10-15%). It is more common in males. DFSP often mimics a scar in presentation. DFSP presents as a pink nodule which may occasionally ulcerate. It also presents as a firm, flesh-colored to brown plaque (Figures 1 and 2). These may become highly indurated and exophytic. These tumors rarely metastasize, but they are locally aggressive.¹

The differential diagnosis includes atypical fibroxanthoma, dermatofibroma, fibrosarcoma, and nodular fasciitis. DFSP can be differentiated from fibrosarcomas in that they are usually shallower in depth and have less cytologic atypia. Fibrosarcomas also may contain mucinous stroma with multinucleated giant cells, unlike DFSP. In addition, DFSP is positive for CD34 immunohistochemical stains, while dermatofibroma is positive for coagulation factor XIIIa. Atypical fibroxanthomas are usually more pleomorphic and less infiltrative than DFSP. Furthermore, multinucleated giant cells and solar elastosis can be found in fibroxanthomas but not in DFSP. The pigmented variant, also known as Bednar tumor, is composed of spindle cells with melanin-containing dendritic cells. This only represents 1% of all DFSP subtypes. The myxoid subtype has a myxoid stromal pattern with multinodular growth and numerous blood vessels. The giant cell fibroblastoma subtype of DFSP appears similar to the pigmented variant, but with myxoid stroma and pseudo- vascular spaces containing multinucleated giant cells. This occurs mostly in children. The fibrosarcomatous subtype is a low-grade form with interspersed cellular atypia and increased mitoses. Interestingly, the fibrosarcomatous foci are either weakly staining for CD34 or are CD34 negative, while the areas not containing cellular atypia (more representative of classic DFSP) are CD34 positive.² Pathology shows atypical spindle cells of fibroblast origin surrounding a core of collagen.³

The definitive treatment of DFSP is surgical excision.¹ Wide local excision with 3-centimeter margins yields less recurrence than simple excision. Nevertheless, wide local excision still has about a 20% recurrence rate. Common practice is to perform deeper excisions containing subcutaneous fat, underlying fascia, and even periosteum and bone. The recommended margin is 2 to 3 centimeters. To date, a handful of studies have reported the outcomes of patients with various excisional margins, as summarized in Table 1.^{2, 4-17} Mohs micrographic surgery has also been used for the surgical treatment of DFSP. Due to the precise and real-time tumor mapping of this technique, maximal tissue sparing can be achieved. Furthermore, this technique is more likely to yield complete surgical clearance without recurrence, especially since this tumor grows asymmetrically and may have several eccentric projections throughout the dermis. Some trials have demonstrated recur-