Hybrid schwannoma/perineurioma: a report of two cases including a possible radiation-induced case.

Hybrid schwannoma/perineurioma represents a recently characterized dermal or subdermal tumor showing schwannian cytomorphology and a perineurioma-like architecture composed of an admixture of both cell types. We report two additional cases of hybrid schwannoma/ perineurioma, one of which occurred after irradiation. Patient 1 was that of a 33-year-old man presented with a 2.8-cm dermal tumor on his left lower leg. Patient 2 was that of an 89-year-old woman with a history of uterine carcinoma treated by surgery and radiation therapy at the age of 35. She presented with a 1.2 × 1.0 cm dermal tumor on her left mons pubis with multiple coincidental basal-cell carcinomas around it. Both tumors were microscopically well circumscribed but unencapsulated and situated in the dermis and adipose tissue and showed a vague storiform and lamellar pattern. Cytologically, both tumors contained two-cell populations, i.e. spindled cells with plump nuclei, which were positive for S-100 protein and negative for epithelial membrane antigen (EMA), claudin-1 and CD34, as well as cells with very slender nuclei and elongated cytoplasmic processes, which were negative for S-100 protein yet expressed EMA, claudin-1 and CD34. Claudin-1 was a better marker to highlight cells with very slender nuclei than EMA. Both tumors lacked expression of neurofilament.