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Background: Some melanomas closely resemble pigmented spindle cell nevi (PSCN) of Reed histologically. The distinction of these entities is important for clinical management. A recent study showed most PSCN (78%) are fusion-driven, commonly involving NTRK3 (57%). Conversely, BRAF V600E mutations are not characteristic of PSCN but are frequent in melanoma., Objective: In this study, we assessed clinical, histologic and genomic differences between PSCN of Reed and Reed-like melanomas (RLMs)., Methods: We performed BRAF V600E immunohistochemistry (IHC) for 18 PSCN and 20 RLM cases. All 23 benign PSCN cases previously underwent whole transcriptome and targeted DNA sequencing with a 1711 gene panel., Results: We previously demonstrated the majority of PSCN (18 of 23) has chimeric fusions. Among PSCN without a chimeric fusion, BRAF mutations were common. Noncanonical BRAF mutations were identified in 2 of 5 nonfusion cases, and 1 case had a canonical BRAF mutation. Alternatively, 70% of RLM demonstrated a BRAF V600E mutation. RLM also occurred more frequently in older patients., Limitations: The overall sample size was small., Conclusions: In diagnostically challenging cases, ancillary IHC studies can assist in distinguishing PSCN from RLM. Our study suggests positive staining by IHC for BRAF V600E and older age strongly favors a diagnosis of RLM.

The newest World Health Organization classification of skin tumors suggests the elimination of cases with BRAF and NRAS mutations from the categories of Spitz tumors (ST) and Spitz melanoma (SM). The objective of this study is to better characterize the genomics of Spitz neoplasms and assess whether the integration of genomic data with morphologic diagnosis improves classification and prognostication. We performed DNA and RNA sequencing on 80 STs, 26 SMs, and 22 melanomas with Spitzoid features (MSF). Next-generation sequencing data were used to reclassify tumors by moving BRAF and/or NRAS mutated cases to MSF. In total, 81% of STs harbored kinase fusions and/or truncations. Of SMs, 77% had fusions and/or truncations with eight involving MAP3K8. Previously unreported fusions identified were MYO5A-FGFR1, MYO5A-ERBB4, and PRKDC-CTNNB1. The majority of MSFs (84%) had BRAF, NRAS, or NF1 mutations, and 62% had TERT promoter mutations. Only after reclassification, the following was observed: (i) mRNA expression showed distinct clustering of MSF, (ii) six of seven cases with recurrence and all distant metastases were of MSFs, (iii) recurrence-free survival was worse in MSF than in the ST and SM groups (P = 0.0073); and (iv) classification incorporating genomic data was highly predictive of recurrence (OR 13.20, P = 0.0197). The majority of STs and SMs have kinase fusions as primary initiating genomic events. The elimination of BRAF and/or NRAS mutated neoplasms from these categories results in the improved classification and prognostication of melanocytic neoplasms with Spitzoid cytomorphology., (Copyright © 2020 The Authors. Published by Elsevier Inc. All rights reserved.)

Recent advances in next generation sequencing (NGS) have allowed for efficient whole transcriptome sequencing, leading to the identification of important kinase fusions as the primary driver in some melanocytic neoplasms. These fusions typically occur mutually exclusively of one another and other well-known initiating mutations such as BRAF, NRAS, NF1, KIT, and GNAQ. Fusions are found in over 50% of Spitz neoplasms, including ALK, BRAF, NTRK1, NTRK3, ROS1, MET, MAP3K8, and RET. Familiarity with the typical morphologic features of certain fusion-driven melanocytic neoplasms can help with classification, diagnosis, and identification of targeted molecular therapies in malignant cases. Spitz tumors with ALK, NTRK1, and NTRK3 fusions have characteristic morphologic features. BRAF and MAP3K8 fusions, in particular, tend to be epithelioid, high grade, and more frequent in Spitz melanoma than other fusion subtypes. Sporadic cases of pigmented epithelioid melanocytoma may have PRKCA fusions and sheets of monomorphic epithelioid melanocytes. Fusion events are also enriched among melanomas without the key mutations BRAF, NRAS, or NF1. Although NGS is the most reliable method to detect fusions, immunohistochemistry and fluorescence in situ hybridization are cost-effective alternatives in some cases. We describe recent discoveries regarding the role of kinase fusions in melanocytic neoplasms and their associated morphologies., (© 2019 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)

Recent studies have described kinase fusions as the most common initiating genomic events in Spitzoid neoplasms. Each rearrangement generates a chimeric protein with constitutive activation of the tyrosine kinase domain, resulting in the development of a Spitzoid neoplasm. Identifying key initiating genomic events and drivers may assist in diagnosis, prognostication, and management. Retrospective, consecutive search of our database between 2009 and 2018 for Spitzoid neoplasms identified 86 cases. Whole transcriptome mRNA and DNA sequencing (1714 genes) detected 9% of cases (8/86) with structural rearrangements in MAPK genes other than BRAF and 47% (40/86) with kinase fusions previously described in Spitzoid neoplasms. We identified in-frame fusions of MAP3K8-DIPC2, MAP3K8-PCDH7, MAP3K8-UBL3, MAP3K8-SVIL (n=6), and ATP2A2-MAP3K3 (n=1) as well as a p.I103_K104 in-frame deletion of MAP2K1 (n=1), in the absence of well-recognized drivers of melanocytic neoplasia. Fluorescence in situ hybridization validated all cases (n=7) with available tissue. Cases occurred in younger patients (median age 18 y). Morphologically, cases were predominantly epithelioid (P=0.0032), often with some melanin pigment (P=0.0047), and high-grade nuclear atypia (P=0.012). A significant proportion were thought to be Spitzoid melanomas (3/8). Average follow-up time was 11 months. One MAP3K8-DIP2C Spitzoid melanoma involved 4/5 sentinel lymph nodes and led to a complete lymph node dissection with unremarkable follow-up at 9 months. One MAP3K8-DIPC2 atypical Spitz tumor raised concern for recurrence at 10 months and was reexcised. We present a distinct subtype of Spitzoid neoplasm characterized by structural alterations in MAPK genes, which are important to recognize given the potential for treatment with MAPK inhibitors in metastatic cases.