- Common benign tumor of putative Schwann cell origin
- Most often seen in adults, with a female predominance
- May present in any visceral or cutaneous location
- Cutaneous lesions are most common on the trunk and extremities.
- Multiple in up to 10% of cases.
- Presents as a slow-growing mass, which may be painful, often with a verrucous appearance
- Excision is usually curative, but the rare infiltrative variants may recur.
- Rare malignant examples exist.
- Poorly defined dermal or subcutaneous tumor
- Composed of nests or trabeculae of large round to oval cells with abundant granular eosinophilic cytoplasm and small, round, uniform, central nuclei
- Pseudoepitheliomatous hyperplasia of the overlying epidermis is very common in dermal lesions.
- Positive for S-100, CD68, NSE and NKI-C3 (a putative melanoma marker). Sometimes also positive for calretinin and α-inhibin.
- Electron microscopy reveals that the cytoplasm is filled with lysosomes, corresponding to the granules seen on H&E.
- The criteria for malignancy are not well defined. Concerning features are size >5 cm, rapid growth, vascular invasion, necrosis, high mitotic index and pleomorphism.