[500] CD34-Positive Superficial Myxofibrosarcoma: A Potential Diagnostic Pitfall

Steven C Smith, Ann Poznanski, Douglas Fullen, Linglei Ma, Rajiv M Patel. University of Michigan, Ann Arbor, MI; Miraca Life Sciences, Glen Burnie, MD

Background: Myxofibrosarcoma (MFS) arises most commonly in the proximal extremities of elderly, where it may extend into the dermis and/or subcutis and be sampled by superficial punch or shave biopsies. We have encountered superficial CD34-positive cases, which may mimic spindle cell/pleomorphic lipoma as well as other CD34-positive spindle cell tumors. The prevalence of CD34 immunoreactivity in superficial MFS has not been previously assessed.
Design: We performed a systematic review of our institution's experience with MFS, selecting unequivocal MFS cases with superficial (dermal and/or subcutaneous) extension, where limited biopsy samples might have proven diagnostically challenging. Cases were immunostained for CD34 (Clone QBEnd10, 1:100 dilution) and the immunohistochemical results and clinicopathologic characteristics were tabulated.
Results: After review of all MFS diagnoses over 5 years (N=56), we identified a subset where the pattern of superficial extension might complicate diagnosis (subset N=8). These cases presented clinicopathologic parameters consistent with reported MFS cohorts, including age range (52-88y), 4:3 male:female ratio, and wide anatomic distribution. In 6 of 8 cases, benign diagnoses were favored clinically, while in the two remaining cases, intermediate (dermatofibrosarcoma protuberans) and malignant (amelanotic melanoma) diagnoses were favored. A sarcoma was not considered in the clinical differential for any of these cases. Of eight cases, four (50%; 1 low, 1 intermediate, and 2 high grade) demonstrated positive staining for CD34, with diffuse stain of spindled cells and cellular processes. Four additional cases showed no immunoreactivity or equivocal/focal staining for CD34.
Conclusions: Our study demonstrates that CD34 positivity is prevalent in about half of superficial MFS. Thus, MFS should be considered in the differential diagnosis when a pathologist is confronted with a CD34-positive dermal/subcutaneous spindle cell tumor.
Category: Dermatopathology

Monday, March 4, 2013 8:45 AM

Proffered Papers: Section F, Monday Morning

 

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