Abstract

A 30 year old man presented with a nodule on the right wrist that rapidly progressed from a small papule several weeks prior. Clinical examination revealed a 2 cm red, exophytic plaque surrounded by a thick white crust that was clinically suspicious for a pyogenic granuloma. Biopsy was performed revealing a compound proliferation of large spindled and epithelioid melanocytes with associated striking pseudoepitheliomatous hyperplasia. Next gen sequencing demonstrated the presence of TMP3-ALK gene fusion. While acanthosis and hyperkeratosis are an expected finding in Spitz family tumors, marked pseudoepitheliomatous hyperplasia to this degree is extraordinary. The epithelial changes in this biopsy could be secondary to repetitive trauma or exogenous stimulus, but it is also possible the pseudoepitheliomatous changes may be related to the genetic properties of the Spitz tumor itself. Pseudoepitheliomatous hyperplasia has not been commended on in prior studies, but review of these papers shows other examples of TMP3-ALK fusion Spitz tumors with this finding [1]. Phenotypic differences have been documented in Spitz tumors based on different fusion partners with the same tyrosine kinase gene. It is possible the TMP3-ALK combination could stimulate this epithelial hyperplasia. Additional studies are necessary to assess this possibility. 1. Busam KJ, Kutzner H, Cerroni L, Wiesner T. Clinical and pathologic findings of Spitz nevi and atypical Spitz tumors with ALK fusions. Am J Surg Pathol. 2014 Jul;38(7):925-33. doi: 10.1097/PAS.0000000000000187. PMID: 24698967; PMCID: PMC5042334.

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