Abstract

Cellular neurothekeomas are benign dermal mesenchymal neoplasms of uncertain histogenesis, characterized by nested epithelioid or spindled cells. While a gold standard immunohistochemical stain has not been identified, traditionally NKI/C3, PGP9.5, MITF, and S100A6 immunohistochemical stains are utilized with variable expression. In our practice, CD138 (Syndecan-1) expression was incidentally observed in a cellular neurothekeoma, and we sought to investigate whether this is a consistent finding in these tumors. Twenty cases diagnosed as cellular neurothekeoma (2008-2023), including those by morphological characteristics alone, were retrieved for independent review by six dermatopathologists. Immunohistochemical stains were not used for diagnostic purposes in the review. These cases were then evaluated for CD138 immunohistochemical expression. Diffuse CD138 (B-A38, Roche/Ventana) expression in a membranous and reticulated extracellular pattern was observed in 14 of 20 cases (70%). Weak or focal CD138 expression was present in an additional 4 of 20 cases. Two of 20 cases did not express CD138. For each specimen, a melanocyte-specific immunohistochemical stain was used to exclude a melanocytic lesion. Control cases included dermal Spitz’ nevi, xanthogranulomas, and epithelioid fibrous histiocytomas, which did not demonstrate diffuse staining with CD138. Our data suggest that CD138 may be a useful adjunctive marker in the diagnosis of cellular neurothekeoma.