OBJECTIVETo study the clinicopathologic features and differential diagnosis of myxoid dermafibrosarcoma protuberans (DFSP).

METHODSThe clinical and pathologic features of 16 cases of myxoid DFSP were reviewed.

RESULTSThere were altogether 15 males and 1 female. The age of the patients ranged from 11 to 73 years (mean = 47 years and median = 48 years). The commonest site of involvement was trunk (number = 11), followed by shoulder (number = 2), head and neck (number = 2), and extremity (number = 1). Similar to conventional DFSP, most patients presented with a slowly enlarging subcutaneous nodule which showed a rapid recent growth in some cases. Amongst the 16 cases studied, 12 occurred de novo and 4 represented local recurrence. The tumors ranged from 2 to 10 cm in greatest dimension (mean = 5 cm and median = 4 cm). Histologically, they were poorly circumscribed and located in the dermis, with focal infiltration into the underlying subcutaneous tissue. Seven cases were purely myxoid and composed of spindly and stellate cells with delicate arborizing vascular meshwork. The remaining 9 cases were predominantly myxoid (> 50%), with 5 cases containing cellular areas resembling conventional DFSP and 4 cases showing fibrosarcomatous transformation. In addition, foci of giant cell fibroblastoma-like areas were noted in 1 case. Immunohistochemical study showed that the tumors cells were positive for CD34. The staining was weak in the myxoid areas, as compared with conventional DFSP. Of the 4 recurrent cases, one patient developed lung metastases.

CONCLUSIONSMyxoid DFSP represents a rare variant of DFSP and may pose important diagnostic pitfalls. It is especially so if the tumor purely consists of myxoid element. Familiarity with the histologic features helps to avoid misdiagnosis.