Melanocytic Neoplasms With MAP2K1 in Frame Deletions and Spitz Morphology

Role of Targeted Sequencing in Routine Diagnostics of Spitz Melanocytic Neoplasms-An Analysis of 70 Cases

BACKGROUND

There is growing evidence that the Spitz group of melanocytic neoplasms should be restricted to those harboring kinase receptor fusions and HRAS mutations/11p15 amplification. The presence of genomic alterations characteristic of conventional melanomas (BRAF and NRAS mutations) precludes a diagnosis of a Spitz neoplasm. It is often challenging to distinguish Spitz neoplasms from conventional melanomas with spitzoid morphology on histopathological grounds alone.

METHODS

We report a series of 70 consecutive melanocytic tumors in which targeted sequencing was indicated to distinguish Spitz from spitzoid neoplasms and to classify Spitz neoplasms along the biological spectrum.

RESULTS

Final diagnoses incorporating molecular results included 12 conventional melanomas (nine of which with NRAS mutations), five Spitz melanomas, 35 atypical Spitz tumors, eight Spitz nevi, three melanocytic tumors with a MAP2K1 mutation, and seven desmoplastic Spitz nevi/tumors. There were significant discrepancies between initial diagnoses and final diagnoses after incorporating molecular results in 24 (34%) cases, including nine conventional melanomas favored to be Spitz neoplasms and nine Spitz neoplasms favored to be conventional melanomas.

CONCLUSIONS

It is often not possible to reliably distinguish Spitz neoplasms from spitzoid melanocytic tumors without identifying their driver genomic alterations. Applying next-generation sequencing in diagnostically problematic tumors improves diagnostic accuracy.

An Unexpected Finding of a PTPN11 Germline Mutation in a Patient With a Melanocytic Lesion With a Somatic MAP2K1 Mutation. Coincidence or Not?

Melanocytic tumors are a diverse group of lesions and are traditionally classified based on a combination of clinical presentation as well as histological examination. More recently, molecular diagnostics has become an increasingly important part of differentiating different melanocytic lesions in the current WHO standards. This molecular testing, however, can result in unexpected findings. In this report, we describe that molecular testing of a clinical atypical melanocytic lesion showed a mutation in the MAP2K1 gene as well as an unexpected germline mutation in PTPN11, indicative of Noonan syndrome. Based on these findings we concluded that the patient had a MAP2K1 associated melanocytic lesion with Noonan syndrome as an incidental finding. Melanomas are classically not associated with Noonan syndrome. However, we hypothesized that the germline mutations of PTPN11 and the somatic second hit mutation in the MAP2K1 genes might be involved in the formation of the aforementioned lesion. As they are both part of the RAS-MAPK pathway. Furthermore, with the expansion of molecular diagnostics in melanomas, we expect to find an increase in unexpected (germline) mutations.

Computational pharmacology profiling of borapetoside C against melanoma

Melanoma,also known as a 'black tumor', begins in the melanocytes when cells (that produce pigment) grows out of control. Immunological dysregulation, which raises the risk for multiple illnesses, including melanoma, may be influenced by stress tiggered through viral infection, long term effects of ultraviolet radiation, environmental pollutants etc. Borapetoside C is one of the phytoconstituents from Tinospora crispa, and its biological source has been reported for its antistress property. Network pharmacology and KEGG pathway analysis of borapetoside C-regulated proteins were conducted to identify the hub genes involved in melanoma development. Further, a molecular docking was performed between borapetoside C and targets involved in melanoma. Further, the top 3 complexes were selected based on the binding energy to conduct molecular dynamics simulations to evaluate the stability of ligand-protein complex followed by principal component analysis and dynamic cross-correlation matrix. In addition, borapetoside C was also screened for its pharmacokinetics and toxicity profile. Network Pharmacology studies and KEGG pathway analysis revealed 8 targets involved in melanoma. Molecular docking between borapetoside C and targets involved in melanoma identified 3 complexes with minimum binding i.e. borapetoside C- MAP2K1, MMP9, and EGFR. Further, molecular dynamics simulations showed a stable complex of borapetoside C with MMP9 and EGFR. The present study suggested that borapetoside C may target MMP9 and EGFR to possess an anti-melanoma property. This finding can be useful in developing a novel therapeutic agent against melanoma from a natural source.Communicated by Ramaswamy H. Sarma.

Atypical Spitz tumor with SQSTM1::NTRK2 fusion: Report of a case with unique spindled cell features

A host of signature genetic alterations have been demonstrated in Spitz neoplasms, most notably fusions of kinase genes (including BRAF, ALK, ROS1, NTRK1, NTRK3, RET, MET, MAP3K8) or variants in HRAS. While there are multiple reports of rearrangements involving NTRK1 and NTRK3 in Spitz tumors, there are very few reports of NTRK2-rearranged Spitz nevi in the literature. This report presents an NTRK2-rearranged atypical Spitz tumor with spindled cell features. The patient was a 6-year-old female with a growing pigmented papule on the back. Histopathological evaluation revealed an asymmetric, biphasic, compound proliferation of melanocytes featuring an epithelioid cell population arranged as variably sized nests and single cells along the basal layer with extension down adnexa, as well as a population of spindled melanocytes with desmoplastic features and loss of Melan-A expression in the dermis. There was partial loss of p16 expression in the epidermal component and diffuse loss in the dermal component. Immunohistochemistry for PRAME, ALK, NTRK1, HRAS Q61R, p53, and BRAF V600E were negative. A SQSTM1::NTRK2 fusion was identified by RNA sequencing. No TERT promoter hotspot variants were detected. This case report expands the known histopathologic spectrum of genetic alterations in Spitz neoplasms.

Spitz Melanocytic Tumors: A Fascinating 75-Year Journey

Over the last 75 years, our understanding of Spitz lesions has undergone substantial evolution. Initially considered a specific type of melanoma, the perception has shifted towards recognizing Spitz lesions as a spectrum comprising Spitz nevi, Spitz melanocytomas, and Spitz melanomas. Spitz lesions are known for posing a significant diagnostic challenge regarding the distinction between benign neoplasms displaying atypical traits and melanomas. A comprehensive understanding of their molecular basis and genomic aberrations has significantly improved precision in classifying and diagnosing these challenging lesions. The primary aim of this review is to encapsulate the current understanding of the molecular pathogenesis and distinct clinicopathologic characteristics defining this intriguing set of tumors.

Spitz Tumors and Melanoma in the Genomic Age: A Retrospective Look at Ackerman's Conundrum

After 25 years, "Ackerman's conundrum", namely, the distinction of benign from malignant Spitz neoplasms, remains challenging. Genomic studies have shown that most Spitz tumors harbor tyrosine and serine/threonine kinase fusions, including ALK, ROS1, NTRK1, NTRK2, NTRK3, BRAF and MAP3K8, or some mutations, such as HRAS and MAP3K8. These chromosomal abnormalities act as drivers, initiating the oncogenetic process and conferring basic bio-morphological features. Most Spitz tumors show no additional genomic alterations or few ones; others harbor a variable number of mutations, capable of conferring characteristics related to clinical behavior, including CDKN2A deletion and TERT-p mutation. Since the accumulation of mutations is gradual and progressive, tumors appear to form a bio-morphologic spectrum, in which they show a progressive increase of clinical risk and histological atypia. In this context, a binary classification Spitz nevus-melanoma appears as no longer adequate, not corresponding to the real genomic substrate of lesions. A ternary classification Spitz nevus-Spitz melanocytoma-Spitz melanoma is more adherent to the real neoplastic pathway, but some cases with intermediate ambiguous features remain difficult to diagnose. A prognostic stratification of Spitz tumors, based on the morphologic and genomic characteristics, as a complement to the diagnosis, may contribute to better treatment plans for patients.

Clinical, Morphologic, and Molecular Features of Benign and Intermediate-grade Melanocytic Tumors With Activating Mutations in MAP2K1

Activating mutations in MAP2K1 can be seen in benign and intermediate-grade melanocytic neoplasms with spitzoid morphology. We analyzed the clinical, histopathologic, and genetic features for 16 cases of benign and intermediate-grade melanocytic tumors harboring activating MAP2K1 mutations. We compared them to Spitz neoplasms with characteristic Spitz fusions or HRAS mutation. We also compared the mutational pattern of benign and intermediate-grade MAP2K1 -mutated neoplasms and melanomas with activating MAP2K1 mutations. Among the 16 cases, the favored morphologic diagnosis was Spitz nevus (8/16), atypical Spitz tumors (6/16), and deep penetrating nevus (2/16). The 2 most common architectural patterns seen included a plaque-like silhouette with fibroplasia around the rete reminiscent of a dysplastic nevus (n=7) or a wedge-shaped or nodular pattern with the plexiform arrangement of the nests aggregating around the adnexa or neurovascular bundle (n=8). The cases with dysplastic architecture and spitzoid cytology resembled dysplastic Spitz nevi. Compared with true Spitz neoplasms, MAP2K1 -mutated neoplasms occurred in older age groups and had more frequent pagetosis and a lower average mitotic count. The most common type of mutation in the benign and intermediate-grade cases in the literature involves an in-frame deletion, while, in melanomas, missense mutations are predominant. Benign and intermediate-grade melanocytic neoplasms with activating mutations in MAP2K1 can have morphologic overlap with Spitz neoplasms. A significant proportion of melanomas also have activating MAP2K1 mutations. In-frame deletions are predominantly seen in the benign and intermediate-grade cases, and missense mutations are predominantly seen in melanomas.

MAP2K1-mutated melanocytic tumors have reproducible histopathologic features and share similarities with melanocytic tumors with BRAF V600E mutations

BACKGROUND

Melanocytic tumors driven by MAP2K1 in-frame deletions are among the most recently described class of melanocytic neoplasms. The reported range of diagnoses and associated genomic aberrations in these neoplasms is wide and includes melanomas, deep penetrating melanocytomas, and pigmented epithelioid melanocytoma. However, little is known about the characteristics of these tumors, especially in the absence of well-known second molecular "hits." Moreover, despite their frequent spitzoid cytomorphology, their potential categorization among the Spitz tumors is debatable.

MATERIALS AND METHODS

We conducted a retrospective search through our molecular archives to identify sequenced melanocytic tumors with MAP2K1 in-frame deletions. We reviewed the clinical and histomorphological features of these tumors and compared them to similar neoplasms reported to date. In addition, we performed single-nucleotide polymorphism (SNP) array testing to identify structural chromosomal aberrations.

RESULTS

Of 27 sequenced tumors, 6 (22%) showed a pathogenic MAP2K1 in-frame deletion (with or without insertion) and were included in this series. Five (83%) were females with lesions involving the upper limb. Histopathologically, all neoplasms were compounded with plaque-like or wedge-shaped silhouettes, spitzoid cytomorphology, and impaired cytologic maturation. All cases showed background actinic damage with sclerotic stroma replacing solar elastosis, variable pagetoid scatter, and occasional dermal mitotic figures (range 1-2/mm2 ). Five cases (83%) had a small component of nevic-looking melanocytes. Biologically, these tumors likely fall within the spectrum of unusual nevi. Five cases (83%) had a relatively high mutational burden and four (67%) showed an ultraviolet radiation signature. Four cases (67%) showed in-frame deletion involving the p.I103_K104del locus while two cases (33%) showed in-frame deletion involving the p.Q58_E62del locus. SNP array testing showed structural abnormalities ranging from 1 to 5 per case. Five of these cases showed a gain of chromosome 15 spanning the MAP2K1 gene locus.

DISCUSSION AND CONCLUSION

Melanocytic tumors with MAP2K1 in-frame deletion could represent another spectrum of melanocytic tumors with close genotypic-phenotypic correlation. They are largely characterized by a spectrum that encompasses desmoplastic Spitz nevus as shown in our series and Spitz and Clark nevus as shown by others. Evolutionary, they share many similarities with tumors with BRAF V600E mutations, suggesting they are better classified along the conventional pathway rather than the Spitz pathway despite the frequent spitzoid morphology.

A reappraisal of the epidemiology of Spitz neoplasms in the molecular era: A retrospective cohort study

BACKGROUND

Previous studies suggest that Spitz neoplasms occur primarily in younger patients, leading pathologists to shy away from diagnosing a benign Spitz neoplasm in the elderly. With the advent of genomic sequencing, there is a need for reappraisal of the epidemiology of Spitz neoplasms in the modern molecular era.

OBJECTIVE

We aim to reassess the epidemiology of Spitz neoplasms incorporating next-generation sequencing.

METHODS

We looked at 53,814 non-Spitz neoplasms and 1260 Spitz neoplasms including 286 Spitz neoplasms with next-generation sequencing testing and collected various epidemiologic data.

RESULTS

In our general pool of cases, the proportion of Spitz neoplasm cases occurring is relatively the same in each of the first 4 decades of life with a precipitous drop in the fifth decade. In assessing a group of genomically verified cases of Spitz neoplasms, the drop was much less significant and up to 20% of all Spitz neoplasm cases occurred in patients over 50 years of age.

LIMITATIONS

Limitations included the number of genetically verified Spitz neoplasm cases available and a possible bias as to which cases undergo genomic testing.

CONCLUSION

Genomic verification may allow more confident diagnosis of Spitz neoplasms in patients over 50 years of age and avoid melanoma overdiagnosis.

An update on genomic aberrations in Spitz naevi and tumours

Spitz neoplasms continue to be a diagnostic challenge for dermatopathologists and are defined by distinctive morphological and genetic features. With the recent advancements in genomic sequencing, the classification, diagnosis, and prognostication of these tumours have greatly improved. Several subtypes of Spitz neoplasms have been identified based on their specific genomic aberrations, which often correlate with distinctive morphologies and biological behaviour. These genetic driver events can be classified into four major groups, including: (1) mutations [HRAS mutations (with or without 11p amplification) and 6q23 deletions]; (2) tyrosine kinase fusions (ROS1, ALK, NTRK1-3, MET and RET); (3) serine/threonine kinase fusions and mutations (BRAF, MAP3K8, and MAP2K1); and (4) other rare genomic aberrations. These driver genomic events are hypothesised to enable the initial proliferation of melanocytes and are often accompanied by additional genomic aberrations that affect biological behaviour. The discovery of theses genomic fusions has allowed for a more objective definition of a Spitz neoplasm. Further studies have shown that the majority of morphologically Spitzoid appearing melanocytic neoplasms with aggressive behaviour are in fact BRAF or NRAS mutated tumours mimicking Spitz. Truly malignant fusion driven Spitz neoplasms may occur but are relatively uncommon, and biomarkers such as homozygous 9p21 (CDKN2A) deletions or TERT-p mutations can have some prognostic value in such cases. In this review, we discuss the importance and various methods of identifying Spitz associated genomic fusions to help provide more definitive classification. We also discuss characteristic features of the various fusion subtypes as well as prognostic biomarkers.

Attempting to Solve the Pigmented Epithelioid Melanocytoma (PEM) Conundrum: PRKAR1A Inactivation Can Occur in Different Genetic Backgrounds (Common, Blue, and Spitz Subgroups) With Variation in Their Clinicopathologic Characteristics

Pigmented epithelioid melanocytoma is a rare cutaneous melanocytic proliferation considered high-grade melanocytoma in the 2018 WHO Classification of Skin Tumors. Little has been reported about the associated genetic drivers in addition to BRAF and MAP2K1 mutations or PRKCA gene fusions. Here, we present a series of 21 cases of PRKAR1A -inactivated melanocytic tumors in which we could assess the associated genetic background. We identified 9 different driver genes related to the common, Spitz, blue nevi, and PRKC -fused groups. Nine cases were associated with a canonical BRAF p.V600E mutation, a hallmark of the common nevus group. They occurred mainly in young adults. All were combined (biphenotypic) cases with a variable proportion of compound nevus. The pigmented epithelioid melanocytoma component was made of thin fascicules or isolated epithelioid cells covered by a dense hyperpigmented melanophage background and was predominantly located in the upper dermis. One such case was malignant. Six cases were associated with Spitz-related genetic anomalies ranging from HRAS or MAP2K1 mutations to gene fusions involving MAP3K8 , MAP3K3 , and RET . They occurred mainly in children and young adults. Morphologically, they showed large confluent junctional nests in a hyperplastic epidermis and a fascicular dermal component of spindled and epithelioid melanocytes with a frequent wedged silhouette. Intravascular invasion was observed in 4/6 cases. Five cases were associated with canonical mutations of the blue nevus group with 4 CYSLTR2 p.L129Q and 1 GNAQ p.Q209L mutations. They were removed mainly in adults and showed a frequent junctional component with epidermal hyperplasia. The dermal component showed dense fascicules of spindled and epithelioid melanocytes predominating over melanophages. One case occurred in a PRKCA -fused tumor in an adolescent with classic morphologic features. These results could potentially shift the concept of PRKAR1A -inactivated melanocytoma, changing from a rather unified model to a more complex one, including genetic subgroup variations with clinical and morphologic specificities. The genetic background of PRKAR1A -inactivated melanocytic tumors should be systematically explored to better understand the extent and clinical behavior of these complex lesions.

The Spectrum of Spitz Melanocytic Lesions: From Morphologic Diagnosis to Molecular Classification

Spitz tumors represent a distinct subtype of melanocytic lesions with characteristic histopathologic features, some of which are overlapping with melanoma. More common in the pediatric and younger population, they can be clinically suspected by recognizing specific patterns on dermatoscopic examination, and several subtypes have been described. We now classify these lesions into benign Spitz nevi, intermediate lesions identified as “atypical Spitz tumors” (or Spitz melanocytoma) and malignant Spitz melanoma. More recently a large body of work has uncovered the molecular underpinning of Spitz tumors, including mutations in the HRAS gene and several gene fusions involving several protein kinases. Here we present an overarching view of our current knowledge and understanding of Spitz tumors, detailing clinical, histopathological and molecular features characteristic of these lesions.

Novel insights into the BAP1-inactivated melanocytic tumor

BAP1-inactivated melanocytic tumor (BIMT) is a group of melanocytic neoplasms with epithelioid cell morphology molecularly characterized by the loss of function of BAP1, a tumor suppressor gene located on chromosome 3p21, and a mutually exclusive mitogenic driver mutation, more commonly BRAF. BIMTs can occur as a sporadic lesion or, less commonly, in the setting of an autosomal dominant cancer susceptibility syndrome caused by a BAP1 germline inactivating mutation. Owing to the frequent identification of remnants of a conventional nevus, BIMTs are currently classified within the group of combined melanocytic nevi. "Pure" lesions can also be observed. We studied 50 BIMTs from 36 patients. Most lesions were composed of epithelioid melanocytes of varying size and shapes, resulting extreme cytomorphological heterogeneity. Several distinctive morphological variants of multinucleated/giant cells were identified. Some hitherto underrecognized microscopic features, especially regarding nuclear characteristics included nuclear blebbing, nuclear budding, micronuclei, shadow nuclei, peculiar cytoplasmic projections (ant-bear cells) often containing micronuclei and cell-in-cell structures (entosis). In addition, there were mixed nests of conventional and BAP1-inactivated melanocytes and squeezed remnants of the original nevus. Of the 26 lesions studied, 24 yielded a BRAF mutation, while in the remaining two cases there was a RAF1 fusion. BAP1 biallelic and singe allele mutations were found in 4/22 and 16/24 neoplasms, respectively. In five patients, there was a BAP1 germline mutation. Six novel, previously unreported BAP1 mutations have been identified. BAP1 heterozygous loss was detected in 11/22 lesions. Fluorescence in situ hybridization for copy number changes revealed a related amplification of both RREB1 and MYC genes in one tumor, whereas the remaining 20 lesions studied were negative; no TERT-p mutation was found in 14 studied neoplasms. Tetraploidy was identified in 5/21 BIMTs. Of the 21 patients with available follow-up, only one child had a locoregional lymph node metastasis. Our results support a progression of BIMTs from a conventional BRAF mutated in which the original nevus is gradually replaced by epithelioid BAP1-inactivated melanocytes. Some features suggest more complex underlying pathophysiological events that need to be elucidated.

The Morpho-Molecular Landscape of Spitz Neoplasms

Spitz neoplasms are a heterogeneous group of melanocytic proliferations with a great variability in the histological characteristics and in the biological behavior. Thanks to recent discoveries, the morpho-molecular landscape of Spitz lineage is becoming clearer, with the identification of subtypes with recurrent features thus providing the basis for a more solid and precise tumor classification. Indeed, specific mutually exclusive driver molecular events, namely HRAS or MAP2K1 mutations, copy number gains of 11p, and fusions involving ALK, ROS, NTRK1, NTRK2, NTRK3, MET, RET, MAP3K8, and BRAF genes, correlate with distinctive histological features. The accumulation of further molecular aberrations, instead, promotes the increasing malignant transformation of Spitz neoplasms. Thus, the detection of a driver genetic alteration can be achieved using the appropriate diagnostic tests chosen according to the histological characteristics of the lesion. This allows the recognition of subtypes with aggressive behavior requiring further molecular investigations. This review provides an update on the morpho-molecular correlations in Spitz neoplasms.

Gene Expression and Mutational Profile in BAP-1 Inactivated Melanocytic Lesions of Progressive Malignancy from a Patient with Multiple Lesions

BAP-1 (BRCA1-associated protein 1) inactivated melanocytic lesions are a group of familial or sporadic lesions with unique histology and molecular features. They are of great clinical interest, at least in part due to the potential for malignant transformation and association with a familial cancer predisposition syndrome. Here, we describe a patient with multiple spatially and temporally distinct melanocytic lesions with loss of BAP1 expression by immunohistochemistry. RNA sequencing was performed on three independent lesions spanning the morphologic spectrum: a benign nevus, an atypical tumor, and a melanoma arising from a pre-existing BAP1-inactivated nevus. The three lesions demonstrated largely distinct gene expression and mutational profiles. Gene expression analysis revealed that genes involved in receptor protein kinase pathways were progressively upregulated from nevus to melanoma. Moreover, a clear enrichment of genes regulated in response to UV radiation was found in the melanoma from this patient, as well as upregulation of MAPK pathway-related genes and several transcription factors related to melanomagenesis.

A Comprehensive Update of the Atypical, Rare and Mimicking Presentations of Mycosis Fungoides

Introduction

Mycosis fungoides (MF) is the most frequent subtype of primary cutaneous T cell lymphomas (pCTCL). The diagnosis may be particularly difficult in the early stages as well as in atypical and rare clinical presentations. Furthermore, MF may simulate a large variety of common dermatologic disorders and patterns, both histopathologically and clinically.

Methods

A literature search was performed to provide a comprehensive update on the rare and atypical MF manifestations as well as the dermatoses and dermatological patterns that could be imitated by MF.

Results

A total of 114 publications were found describing a series of different dermatoses and dermatological patterns mimicked by MF, as well as some particular localizations of MF lesions and dermatoses that occur in preexisting MF lesions.

Conclusions

The number of dermatoses that can be imitated by MF is ever-increasing. Patients with common dermatologic conditions that prove to be treatment refractory should be biopsied without delay, and sequentially as necessary, to prevent delay in diagnosis and progression of disease. Clinicopathologic correlation is the best way of diagnosis.

Spitz nevus with a novel TFG-NTRK2 fusion: The first case report of NTRK2-rearranged Spitz/Reed nevus

Fusions of ALK, ROS1, NTRK1, NTRK3, RET, MET, MERTK, FGFR1, ERBB4, LCK, BRAF, MAP3K8, MAP3K3, and PRKDC and mutation of HRAS have so far been discovered as the genetic alterations associated with the pathogenesis of Spitz neoplasms. This report presents the first case of NTRK2-rearranged Spitz/Reed nevus. The patient was a 39-year-old male with a pigmented macule rapidly growing on his shoulder. Histopathologically, the lesion was a junctional melanocytic nevus composed of large nests of spindled melanocytes with abundant eosinophilic cytoplasm associated with a hyperplastic epidermis. These findings fulfilled the diagnostic criteria of a pigmented spindle cell nevus of Reed (variant of Spitz nevus). Immunohistochemistry for pan-Trk revealed diffuse cytoplasmic positivity in the tumor cells, but immunoexpression of ALK, ROS1, and BRAF V600E was not seen. A novel, in-frame, TFG-NTRK2 fusion was identified by RNA sequencing. This case report expands the list of genetic alterations in Spitz neoplasms and the spectrum of NTRK2-rearranged tumors.

NGS-Based Analysis of Atypical Deep Penetrating Nevi

Simple Summary

The recent WHO classification of melanocytic tumors requires the implementation of combined phenotypic–genotypic diagnostics. For rare tumors, such as atypical deep penetrating nevi, there is insufficient information regarding genetic status, and it is not yet clear whether the observed unusual morphological cyto-architectures reflect a distinct genomic profile or are associated with an increased metastatic potential and aggressive clinical behavior. We report herein a comprehensive next-generation sequencing (NGS) analysis of a series of atypical DPNs, showing their mutational profile with some specific signatures for these rare and diagnostically challenging tumors.

Abstract

Deep penetrating nevi (DPNs) are rare melanocytic neoplasms consisting of pigmented spindled or epithelioid melanocytes with a distinctive wedge-shaped configuration showing activation of the WNT pathway, with unusual cyto-architectural features. It is unclear whether they show a distinct genomic profile associated with a diverse metastatic potential. We describe herein a cohort of 21 atypical DPNs analyzed by next-generation sequencing using the Ion AmpliSeq™ Comprehensive Cancer Panel. We found that β-catenin exon 3 was mutated in 95% and MAP kinase pathway genes in 71% of the cases. Less frequent mutations were observed in HRAS (19%) and MAP2K1 (24%). Isocitrate dehydrogenases 1 (IDH1) mutations, including R132C, V178I, and S278L, were identified in 38% of cases and co-existed with BRAF/HRAS mutations. The only case with progressive nodal disease carried alterations in the β-catenin pathway and mutations in IDH1 and NRAS (codon 61). By a comprehensive mutation analysis, we found low genetic heterogeneity and a lack of significant associations between specific gene mutations and histopathological features, despite atypical features. Whether the acquisition of an NRAS or IDH1 mutation in an atypical DPN may represent a molecular evolution implying a pathway to melanoma progression should be confirmed in a larger series.