Rosette‐like structures in the spectrum of spitzoid tumors

Abstract

Background Spitz nevi demonstrate a diverse spectrum of morphologies. Recently, there have been two reported examples of Spitz nevi with rosette‐like structures similar to Homer‐Wright rosettes. Rosettes have also been described in melanomas and in a proliferative nodule arising in a congenital nevus. Methods A retrospective review of 104 cases of Spitz nevi and variants (n = 51), pigmented spindle cell nevi (n = 26), combined melanocytic nevi with features of Spitz (n = 8), atypical Spitz tumor ( AST , n = 9), and spitzoid melanoma (n = 10). Results Rosette‐like structures were present in 3 of the 104 cases (2.9%), including a compound Spitz nevus, a desmoplastic Spitz nevus, and an AST . All three cases demonstrated several foci of small nests of epithelioid cells with peripherally palisaded nuclei arranged around a central area of fibrillar eosinophilic cytoplasm. Immunohistochemical staining of the three spitzoid lesions demonstrated that the rosette‐like structures express S100 protein, Melan‐A, and neuron specific enolase ( NSE ) and lacked expression of neurofilament, glial fibrillary acidic protein and synaptophysin. Conclusions While uncommon, rosette‐like structures can occur as a focal feature in Spitz nevi and AST . Rosette‐like structures may represent a normal morphologic finding in Spitz nevi, and awareness of them may prevent misdiagnosis as a neural tumor or melanoma.