S-100

The lesion is subepithelial in location and consists of a well-demarcated, but not encapsulated proliferation of benign spindle cells.

The tumor consists of interlacing fascicles of bland fusiform cells. There are focal palisades of nuclei sufficiently prominent to be designated Verocay bodies. No mitotic activity is identified.

The tumor is strongly immunoreactive for S-100 (cytoplasmic and nuclear), and non-reactive for epithelial membrane antigen (EMA). There is no evident mitotic activity.

S-100is structurally similar to calmodulin and gets its name from the fact that it is 100% soluble in ammonium sulfate at neutral pH.