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Case Reports

Abstract

Spitz melanocytic neoplasms (SMNs) exhibit frequent chromosomal rearrangements, resulting in recurring gene fusions, such as ALK fusions. While TPM3 and DCTN1 are the predominant fusion partners of ALK, less common partners like NPM1, TPR, CLIP1, GTF3C2, MLPH, EEF2, MYO5A, and KANK1 have also been documented. Although ALK fusions are primarily associated with Spitz nevi or atypical Spitz tumors, instances of Spitz melanoma (SM) with ALK fusions documented in the English literature are exceedingly rare. Here, we present a case of SM harboring SLC20A1::ALK fusion, a novel fusion previously undescribed in SMNs, including SMs. The patient, a 13-year-old female, presented with a papule on the left leg. Histopathologically, tumor cells exhibited spitzoid morphology, forming small nests or singly-arranged cells in the dermis, expressing PRAME and ALK. Increased mitotic activity, including deep dermal and atypical mitotic figures, was observed (up to 3 mitotic figures/mm²). Chromosomal microarray analysis detected five copy number losses and one gain, while fluorescence in situ hybridization revealed borderline positive chromosomal aberrations involving 6p25, 8q24, and 11q13. Next-generation sequencing identified SLC20A1::ALK fusion and a somatic mutation in GRM3. These findings supported a diagnosis of SM. Subsequent wide local excision and sentinel lymph node biopsy revealed scar and melanoma (Breslow thickness: 1.9 mm) and a focus of metastatic melanoma in a lymph node (pT2apN1a). To the best of our knowledge, this case represents the first report of SLC20A1::ALK fusion in SM, contributing to the expanding body of literature on ALK-fused SMNs.