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Spitz melanoma is a distinct subset of spitzoid melanoma


Melanomas that have histopathologic features that overlap with those of Spitz nevus are referred to as spitzoid melanomas. However, the diagnostic concept is used inconsistently and genomic analyses suggest it is a heterogeneous category. Spitz tumors, the spectrum of melanocytic neoplasms extending from Spitz nevi to their malignant counterpart Spitz melanoma, are defined in the 2018 WHO classification of skin tumors by the presence of specific genetic alterations, such as kinase fusions or HRAS mutations. It is unclear what fraction of “spitzoid melanomas” defined solely by their histopathologic features belong to the category of Spitz melanoma or to other melanoma subtypes. We assembled a cohort of 25 spitzoid melanomas diagnosed at a single institution over an 8-year period and performed high-coverage DNA sequencing of 480 cancer related genes. Transcriptome wide RNA sequencing was performed for select cases. Only nine cases (36%) had genetic alterations characteristic of Spitz melanoma, including HRAS mutation or fusion involving BRAF, ALK, NTRK1, or MAP3K8. The remaining cases were divided into those with an MAPK activating mutation and those without an MAPK activating mutation. Both Spitz melanoma and spitzoid melanomas in which an MAPK-activating mutation could not be identified tended to occur in younger patients on skin with little solar elastosis, infrequently harbored TERT promoter mutations, and had a lower burden of pathogenic mutations than spitzoid melanomas with non-Spitz MAPK-activating mutations. The MAPK-activating mutations identified affected non-V600 residues of BRAF as well as NRAS, MAP2K1/2, NF1, and KIT, while BRAF V600 mutations, the most common mutations in melanomas of the WHO low-CSD category, were entirely absent. While the “spitzoid melanomas” comprising our cohort were enriched for bona fide Spitz melanomas, the majority of melanomas fell outside of the genetically defined category of Spitz melanomas, indicating that histomorphology is an unreliable predictor of Spitz lineage.

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Fig. 1: Spitz melanomas with HRAS mutations share features with HRAS mutant Spitz nevi.
Fig. 2: Histopathology of Spitz melanomas with BRAF fusions.
Fig. 3: Spitz melanoma with ALK fusion.
Fig. 4: Rosette-like structures in Spitz melanoma with NTRK1 fusion.
Fig. 5: Spitzoid melanoma with a class 3 BRAF mutation.
Fig. 6: Spitzoid melanomas with NRAS mutation.
Fig. 7: Genetic alterations in spitzoid melanomas.


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We thank Connie Jang and Yvonne Lee for their assistance in organizing and obtaining the cases. SR was funded in part by the American Society of Dermatopathology Mentorship Award, and Sandra Peternel was supported by a grant from the European Academy of Dermatology and Venereology (RF-2017-17). This work was supported by the National Cancer Institute at the National Institutes of Health (grant number 1R35CA220481).

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Raghavan, S.S., Peternel, S., Mully, T.W. et al. Spitz melanoma is a distinct subset of spitzoid melanoma. Mod Pathol 33, 1122–1134 (2020).

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