Track: Case Reports

Abstract:

Squamomelanocytic tumors (SMTs) are rare cutaneous neoplasms described as having features of both squamous cell carcinoma (SCC) and malignant melanoma within a single tumor. Herein, we report a case of a 75- year-old male presenting with two concurrent and distinct erythematous, non-healing papular lesions, one of the forearm and one of the back. Histopathologically and immunophenotypically, both lesions consisted of mixed components of SCC and in-situ and invasive malignant melanoma. Immunohistochemistry of both specimens highlighted predominant lesional malignant melanoma cells with HMB45, melanoma cocktail, S100 and SOX10, and squamous carcinoma components highlighted by P40, P63 and CK5 intermixed within the melanocytic population. Targeted molecular testing by next generation sequencing (NGS) showed no reportable variants of BRAF, KIT, or NRAS genes in both tumors. The lesions are presumed independent primaries given both tumors had considerable in-situ melanoma components; however, the distinction between synchronous lesions and metastatic disease is notably challenging. The rarity and unknown pathogenesis of SMTs impose challenges in navigating classification and biological behaviour, however multiple reports have suggested SMTs have better prognosis as compared to pure melanomas, with rare local recurrences and metastasis reported. Current literature suggests tumors be treated as the most aggressive component, in most cases the invasive melanoma. Further work and increased recognition of this unique entity is needed to elucidate the histogenesis which may allow for accurate classification, improved prognostic assessment, and optimization of clinical management. To our knowledge, this is the first reported case of multiple squamomelanocytic tumors concurrently arising in a single patient.

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Andrea Chen