The American Society of Dermatopathology

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Interactive Case Study - November 2023

57-year-old woman with a pretibial nodule

Negin Farsi, MD ; Nicholas A. Zoumberos, MD

Question 1:

A 57-year-old woman presented with a firm, slightly tender, multi-lobulated, slowly growing subcutaneous nodule on the left proximal pretibial region that had been present for a couple of years. A punch biopsy was performed. Histopathologic examination of the biopsy revealed the following features (Figures 1-3). Immunohistochemical stains were performed (Figures 4-7). Tumor cells were negative for desmin, neurofilament, CD31, and HHV-8.

Click this image to view the virtual slide:

Figure 1: 2X 

Figure 2: 10x

Figure 3: 20x 

Figure 4: S100 2x

Figure 5: S100 20x

Figure 6: SMA 2x

Figure 7: SMA 10x

What is the best diagnosis?