Benign cutaneous biphasic hybrid tumor of perineurioma and cellular neurothekeoma: A case report expanding the clinical and histopathologic features of a recently described entity.

Benign cutaneous plexiform hybrid tumor of perineurioma and cellular neurothekeoma (BCPHTPCN) is a recently described entity that presents as a solitary papule in the perioral area. As implied by its name, BCPHTPCN displays microscopic features of both perineurioma and cellular neurothekeoma arranged in a plexiform pattern. We report a case of nonplexiform benign cutaneous biphasic hybrid tumor of perineurioma and cellular neurothekeoma in a 36-year-old woman, who presented with a 4-year history of a firm, flesh-colored left ankle nodule. Histologically, there was a biphasic, well-circumscribed unencapsulated dermal mesenchymal proliferation with no connection to the epidermis, which exhibited mild acanthosis with slightly pigmented basal keratinocytes and overlying parakeratosis. The proliferation consisted of uniform bland spindle cells with bipolar cytoplasmic processes arranged in whorls with interspersed islands of epithelioid cells. Immunohistochemically, the spindle cell component was positive for CD34, EMA, and GLUT-1, consistent with perineurial differentiation, whereas the epithelioid nests were positive for NKI/C3 and MiTF, as expected in neurothekeoma. Stains for S100 protein, SOX10, desmin, claudin, pan-melanoma markers, and NSE were negative. We believe this case expands the histopathologic spectrum of BCPHTPCN showing that it can be grown in a nonplexiform pattern, and we suggest the term benign cutaneous biphasic hybrid tumor of perineurioma and cellular neurothekeoma as a more precise name. It is also, to the best of our knowledge, the first case reported outside the head and neck area.