We report an unusual pattern of paranuclear dot-like expression of CD99 in 14 cases of MCC, two of which did not express CK20. This previously unrecognized expression pattern may be of use in differentiating MCC from other cutaneous malignancies, especially when CK20 expression is limited or absent.

A 20-year-old female initially presented to the emergency room with a 3-day history of painless swelling involving both legs following exercise. A deep vein thrombosis was suspected and excluded, but she continued to have progressive symptoms in her legs over the next 8 months including pain, tightness of muscles, and skin changes (Fig. 1). Magnetic resonance imaging of the bilateral legs was performed (Fig. 2a-c) followed by full thickness skin to muscle biopsy (Fig. 3a-b).

No abstract