UPMC Dermatopathology "Case of the Month" Presentations
UPP - Department of Dermatology, Dermatopathology Unit
Case Authors: Peggy Lin MD, Leena T. Lourduraj MD, Drazen M. Jukic MD PhD
MAY 2005 CASE OF THE MONTH
CLINICAL FINDINGS
An outside dermatologist sent a skin specimen to the UPMC Department of Dermatopathology for a second opinion/consultation. The specimen was removed from the left arm of a 19-year-old female and a request was made to evaluate for a possible smooth muscle tumor of uncertain malignant potential. No clinical history was submitted with the case, which was submitted as a consult slide and consult block.
H&E sections reveal a plaque-like proliferation of plump spindle cells arranged in a plexiform formation (Figure 1). Groups of cells intersect between collagen bundles and envelope individual adnexal structures (Figure 2). Some of the cells have a foamy cytoplasm. A good Grenz zone between this neoplasm and the epidermis is appreciated (Figure 3). The neoplasm extends focally into the subcutis, in a somewhat pushing fashion. Mitotic figures are observed, approaching 1-2/10 HPF (Figure 4)
Immunohistochemistry studies demonstrate that the tumor cells are positive for vimentin, smooth muscle actin, focally with CD68, and there is increased proliferation rate seen with interpretation of Ki67, that focally reaches up to 15%. Other stains performed were myoglobin, myosin heavy chain, S100, CD56- NCAM, CD57, desmin, Factor XIIIa, calponin, smooth muscle myosin heavy chain, CD34, CD31, and tyrosinase were all negative. (Figures 5 and 6)
The histological features and special studies are consistent with atypical myofibroblastic tumor due to the positivity for smooth muscle actin and negativity for desmin.
This is a neoplasm of either fibrohistiocytic or myofibroblastic lineage (atypical plexiform histiocytic tumors could somewhat stain positive with SMA).
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