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Case Reports

Abstract

Atypical spitz nevus/tumor are benign melanocytic tumors showing overlapping features between typical spitz nevus and spitzoid melanoma. The atypical features include large, irregular nuclei with prominent eosinophilic nucleoli, increase mitotic activity, and marked cellular pleomorphism. Molecular studies are useful in spitz neoplasm. We present a case of a 34-year-old male with a slightly painful and growing papule on his penis. On physical examination, there was an erythematous, shiny, smooth, and pedunculated papule on the penile shaft. Microscopic examination showed an exophytic compound spitzoid melanocytic neoplasm.  There were nests of spitzoid melanocytes at the dermal-epidermal junction. In the dermis, there was a sheet-like growth pattern of epithelioid melanocytes with moderate to severe nuclear atypia, prominent pleomorphism, and mitotic activity of 2/mm2. There was maturation with descent. Immunohistochemical stains showed the melanocytic proliferation was positive for MART-1, S100 and SOX10, negative for HMB45 in the dermal component, and negative for AE1/AE3, CD163 and CD68. Ki-67 proliferation index was 1-2%. Also, molecular analysis showed the presence of a MLANA-BRAF fusion. Overall findings were consistent with a diagnosis of a MLANA-BRAF fusion atypical spitz tumor. Two variants of possible clinical significance: ERBB2 p.V482I and FGFR3 p.A391T were also identified. BRAF fusions can be found in 5-6% of Spitz neoplasms. The break point of the BRAF fusion is in intron 8 for MLANA-BRAF. We share this case to report this atypical case, to expand literature on atypical spitz tumor, and to emphasize the importance of molecular studies for definitive diagnosis.