Benign and Intermediate-grade Melanocytic Tumors With BRAF Mutations and Spitzoid Morphology: A Subset of Melanocytic Neoplasms Distinct From Melanoma

A Clinical, Morphologic, and Molecular Comparison of Bonafide Spitz Melanomas and ASTs in the Pediatric Population

Pediatric Spitz melanoma (SM) with bonafide metastatic disease is rare. In this study, we assembled the largest cohort to date of pediatric SM with a verified Spitz-associated genomic driver and clinical follow-up demonstrating bonafide metastasis. We compared the clinical, morphologic, and molecular features of these SMs to a control cohort of 57 pediatric atypical Spitz tumors (ASTs). Pediatric SM patients were significantly older than AST patients (12 vs 8 years of age). While not statistically significant, SMs were more likely to be heavily pigmented (5/7 SMs vs 11/57 ASTs), to have a sheet-like growth pattern (3/7 SMs vs 8/57 ASTs), and have severe nuclear atypia (6/7 SMs vs 20/57 ASTs). SMs had significantly greater mitotic activity (avg of 4.3/mm 2 in SMs and 2.7/mm 2 in ASTs, P =0.008) and more frequent larger cell size ( P =0.006). However, none of these features were specific and could also be seen in ASTs. The presence of homozygous deletions of 9p21 in conjunction with TERT promoter hot spot mutations or PTEN deletions (n=2), as well as MYC overexpression or amplification (n=2) were only seen in the SMs and none of the ASTs. These findings were mutually exclusive in the SM group and mutually exclusive with the presence of complex chromosomal copy number aberrations, which were seen in the remaining 3 pediatric SMs. This study demonstrates that there are multiple pathways to malignancy for pediatric SMs and none of our commonly used biomarkers have a particularly high sensitivity. Hence, the optimal distinction of pediatric SM from ASTs will continue to require the integration of clinical, histologic, and molecular data.

Evaluation and Surgical Management of Pediatric Cutaneous Melanoma and Atypical Spitz and Non-Spitz Melanocytic Tumors (Melanocytomas): A Report From Children's Oncology Group

PURPOSE

The purpose of this study was to develop recommendations for the diagnostic evaluation and surgical management of cutaneous melanoma (CM) and atypical Spitz tumors (AST) and non-Spitz melanocytic tumors (melanocytomas) in pediatric (age 0-10 years) and adolescent (age 11-18 years) patients.

METHODS

A Children's Oncology Group-led panel with external, multidisciplinary CM specialists convened to develop recommendations on the basis of available data and expertise.

RESULTS

Thirty-three experts from multiple specialties (cutaneous/medical/surgical oncology, dermatology, and dermatopathology) established recommendations with supporting data from 87 peer-reviewed publications.

RECOMMENDATIONS

(1) Excisional biopsies with 1-3 mm margins should be performed when feasible for clinically suspicious melanocytic neoplasms. (2) Definitive surgical treatment for CM, including wide local excision and sentinel lymph node biopsy (SLNB), should follow National Comprehensive Cancer Network Guidelines in the absence of data from pediatric-specific surgery trials and/or cohort studies. (3) Accurate classification of ASTs as benign or malignant is more likely with immunohistochemistry and next-generation sequencing. (4) It may not be possible to classify some ASTs as likely/definitively benign or malignant after clinicopathologic and/or molecular correlation, and these Spitz tumors of uncertain malignant potential should be excised with 5 mm margins. (5) ASTs favored to be benign should be excised with 1- to 3-mm margins if transected on biopsy. (6) Re-excision is not necessary if the AST does not extend to the biopsy margin(s) when complete/excisional biopsy was performed. (7) SLNB should not be performed for Spitz tumors unless a diagnosis of CM is favored on clinicopathologic evaluation. (8) Non-Spitz melanocytomas have a presumed increased risk for progression to CM and should be excised with 1- to 3-mm margins if transected on biopsy. (9) Re-excision of non-Spitz melanocytomas is not necessary if the lesion is completely excised on biopsy.

"Pathway Leap": A New Molecular Phenomenon to Consider in the Pathogenesis of Melanocytic Tumors

INTRODUCTION

The current WHO classification of melanocytic tumors distinguishes 9 pathogenic routes. This classification is based on the conceptual interpretation that melanocytic tumors evolve from benign counterparts, accumulating mutations, eventually developing into melanomas with metastatic and potentially lethal capacity. In this article, we present a molecular study of 2 melanocytic tumors that suggest a "leap" from pathogenic routes IV to I.

MATERIALS AND METHODS

Two recent melanocytic tumors were selected, each exhibiting 2 contiguous melanocytic populations of distinct morphology, without separation between them. One population corresponded to a common melanocytic nevus (with morphology consistent with route I), while the other population displayed epithelioid morphology, consistent with route IV. Immunohistochemical studies were performed in both cases, as well as molecular studies using PCR to search for mutations in the NRAS and BRAF genes. For the molecular study, both populations were manually separated by microdissection.

RESULTS

In both cases, the melanocytic population consistent with route I showed a BRAF mutation. In both cases, the epithelioid population did not present a BRAF mutation. No NRAS mutations were observed in any of the populations.

CONCLUSIONS

These findings suggest the existence of a molecular phenomenon of "leap" between pathways, which we have termed "pathway leap." This could explain the enigmatic group of tumors that the WHO classifies under the heading of "combined nevi." This group could be more frequent than suspected, because microdissection is not a technique commonly used in the daily diagnosis of melanocytic tumors.

Spitz tumours and mimickers

Since their initial description in 1948, Spitz tumours have always been a challenge in the field of dermatopathology and paediatric pathology. Advances in molecular pathology have confirmed they are associated with specific anomalies, mainly gene fusions. They display a wide range of clinical presentations and histological subtypes. Most cases are Spitz nevi and very few lesions match the criteria to be diagnosed as atypical Spitz tumours. Even fewer are labelled as Spitz melanomas. Follow-up studies of genetically characterized cases have repeatedly confirmed that, even if the regional lymph node is involved, the overall outcome remains favourable. The aims of this review are to cover the variety of morphological presentations of Spitz tumours and illustrate the most rare subtypes. When possible, we have pointed out the potential trends between some unusual morphological features and the frequently associated genetic drivers. Spitz tumours have many differential diagnoses, the main being superficial spreading melanoma, with overlapping morphological features in early lesions. Essential clues to discriminate Spitz from mimickers have been listed and illustrated.

Spitz melanoma

It has long been recognized that the histopathologic differential diagnosis between Spitz nevus and melanoma is sometimes extraordinarily difficult. Both can be composed of large oval to spindled melanocytes with abundant cytoplasm and large nuclei. Genomic studies over the last decade have clarified that Spitz tumors have diverse genetic initiating events, and that for each of these, there are benign, intermediate grade, and malignant lesions. Another discovery is that some melanomas can resemble Spitz tumors morphologically but have conventional initiating mutations (eg, BRAF and NRAS). The current World Health Organization definition of Spitz tumors restricts the spectrum to neoplasms with an activating mutation affecting the MAP kinase pathway, mostly fusions involving kinase genes. Whether splitting off Spitz tumors from other neoplasms that are only morphologically spitzoid will stand the test of time is uncertain, but for now, it does bring order to what has been a complex area. The recognition of Spitz melanoma will enable classification, follow-up, and the delineation of rational treatment guidelines for this important group of tumors, most of which are in young people. The author reviewed the logic of the World Health Organization definition of Spitz tumors, the spectrum of tumors produced by initiating mutations, and problems with the definition of Spitz melanoma and provides an example of this rare entity in the context of related tumors.

Histological interpretation of spitzoid tumours: an extensive machine learning-based concordance analysis for improving decision making

The histopathological classification of melanocytic tumours with spitzoid features remains a challenging task. We confront the complexities involved in the histological classification of these tumours by proposing machine learning (ML) algorithms that objectively categorise the most relevant features in order of importance. The data set comprises 122 tumours (39 benign, 44 atypical and 39 malignant) from four different countries. BRAF and NRAS mutation status was evaluated in 51. Analysis of variance score was performed to rank 22 clinicopathological variables. The Gaussian naive Bayes algorithm achieved in distinguishing Spitz naevus from malignant spitzoid tumours with an accuracy of 0.95 and kappa score of 0.87, utilising the 12 most important variables. For benign versus non-benign Spitz tumours, the test reached a kappa score of 0.88 using the 13 highest-scored features. Furthermore, for the atypical Spitz tumours (AST) versus Spitz melanoma comparison, the logistic regression algorithm achieved a kappa value of 0.66 and an accuracy rate of 0.85. When the three categories were compared most AST were classified as melanoma, because of the similarities on histological features between the two groups. Our results show promise in supporting the histological classification of these tumours in clinical practice, and provide valuable insight into the use of ML to improve the accuracy and objectivity of this process while minimising interobserver variability. These proposed algorithms represent a potential solution to the lack of a clear threshold for the Spitz/spitzoid tumour classification, and its high accuracy supports its usefulness as a helpful tool to improve diagnostic decision-making.

Restrospective reappraisal of the prognostic classification of spitzoid melanocytic neoplasms after BRAF and NRAS mutation characterisation: a single institution experience

AIMS

The current WHO classification of melanocytic tumours excludes neoplasms showing BRAF or NRAS mutations from the Spitz category. This study aimed to review and reclassify atypical melanocytic tumours with spitzoid morphological features diagnosed between 2009 and 2021 in our hospital after expanding the molecular profile, including BRAF and NRAS mutations in all cases.

METHODS AND RESULTS

A total of 71 neoplasms showing spitzoid features (Spitz-like) and atypia were included. The risk of progression of tumours was first studied by integrating the morphology, immunohistochemistry (p16, Ki67, HMB45 and PRAME) and fluorescence in-situ hybridisation (FISH) results (melanoma multiprobe and 9p21). In a second step, after expanding the molecular study, including BRAF and NRAS mutational status, the neoplasms were finally classified into four subgroups: atypical Spitz tumour (AST, n = 45); BRAF-mutated naevus/low-grade melanocytoma with spitzoid morphology (BAMS, n = 2); Spitz melanoma (SM, n = 14); and BRAF or NRAS mutated melanoma with spitzoid features (MSF, n = 10). Follow-up of patients revealed uneventful results for AST and BAMS. Only one SM presented lymph node metastasis after 134 months. Conversely, patients with MSF showed an unfavourable outcome: three developed lymph node metastases after a mean time of 22 months, with one patient presenting distant metastasis and dying of the disease 64 months from diagnosis. The progression-free survival showed significant differences between the four groups of spitzoid tumours (P < 0.001) and between both melanoma subtypes (P = 0.012).

CONCLUSIONS

The classification and prognostication of atypical neoplasms with spitzoid features requires the integration of histomorphology with the molecular investigation of tumours, which should include BRAF and NRAS mutational status.

BRAF Mutated and Morphologically Spitzoid Tumors, a Subgroup of Melanocytic Neoplasms Difficult to Distinguish From True Spitz Neoplasms

Drivers of Spitz neoplasms include activating point mutations in HRAS and Spitz-associated genomic fusions. It has become evident that some BRAF -mutated melanocytic neoplasms can morphologically mimic Spitz tumors (STs). These have been termed BRAF mutated and morphologically spitzoid (BAMS). In this study, 17 experts from the International Melanoma Pathology Study Group assessed 54 cases which included 40 BAMS and 14 true STs. The participants reviewed the cases blinded to the genomic data and selected among several diagnostic options, including BAMS, ST, melanoma, and other. A total of 38% of all diagnostic selections in the BAMS cases were for BAMS, whereas 32% were for ST. In 22 of the BAMS cases, the favored diagnosis was BAMS, whereas in 17 of the BAMS cases, the favored diagnosis was ST. Among the 20 cases in the total group of 54 with the highest number of votes for ST, half were BAMS. Of BAMS, 75% had a number of votes for ST that was within the SD of votes for ST seen among true ST cases. There was poor interobserver agreement for the precise diagnosis of the BAMS (kappa = 0.16) but good agreement that these cases were not melanoma (kappa = 0.7). BAMS nevi/tumors can closely mimic Spitz neoplasms. Expert melanoma pathologists in this study favored a diagnosis of ST in nearly half of the BAMS cases. There are BAMS cases that even experts cannot morphologically distinguish from true Spitz neoplasms.

Kinase Fusions in Spitz Melanocytic Tumors: The Past, the Present, and the Future

In recent years, particular interest has developed in molecular biology applied to the field of dermatopathology, with a focus on nevi of the Spitz spectrum. From 2014 onwards, an increasing number of papers have been published to classify, stratify, and correctly frame molecular alterations, including kinase fusions. In this paper, we try to synthesize the knowledge gained in this area so far. In December 2023, we searched Medline and Scopus for case reports and case series, narrative and systematic reviews, meta-analyses, observational studies-either longitudinal or historical, case series, and case reports published in English in the last 15 years using the keywords spitzoid neoplasms, kinase fusions, ALK, ROS1, NTRK (1-2-3), MET, RET, MAP3K8, and RAF1. ALK-rearranged Spitz tumors and ROS-1-rearranged tumors are among the most studied and characterized entities in the literature, in an attempt (although not always successful) to correlate histopathological features with the probable molecular driver alteration. NTRK-, RET-, and MET-rearranged Spitz tumors present another studied and characterized entity, with several rearrangements described but as of yet incomplete information about their prognostic significance. Furthermore, although rarer, rearrangements of serine-threonine kinases such as BRAF, RAF1, and MAP3K8 have also been described, but more cases with more detailed information about possible histopathological alterations, mechanisms of etiopathogenesis, and also prognosis are needed. The knowledge of molecular drivers is of great interest in the field of melanocytic diagnostics, and it is important to consider that in addition to immunohistochemistry, molecular techniques such as FISH, PCR, and/or NGS are essential to confirm and classify the different patterns of mutation. Future studies with large case series and molecular sequencing techniques are needed to allow for a more complete and comprehensive understanding of the role of fusion kinases in the spitzoid tumor family.

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.

Diagnosing Cutaneous Melanocytic Tumors in the Molecular Era: Updates and Review of Literature

Over the past decade, molecular and genomic discoveries have experienced unprecedented growth, fundamentally reshaping our comprehension of melanocytic tumors. This review comprises three main sections. The first part gives an overview of the current genomic landscape of cutaneous melanocytic tumors. The second part provides an update on the associated molecular tests and immunohistochemical stains that are helpful for diagnostic purposes. The third section briefly outlines the diverse molecular pathways now utilized for the classification of cutaneous melanomas. The primary goal of this review is to provide a succinct overview of the molecular pathways involved in melanocytic tumors and demonstrate their practical integration into the realm of diagnostic aids. As the molecular and genomic knowledge base continues to expand, this review hopes to serve as a valuable resource for healthcare professionals, offering insight into the evolving molecular landscape of cutaneous melanocytic tumors and its implications for patient care.

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.

TERT Promoter Mutational Analysis as an Ancillary Diagnostic Tool for Diagnostically Challenging Melanocytic Neoplasms

ABSTRACT

Telomerase reverse transcriptase promoter mutations (TPMs) have been shown to be common in melanoma and uncommon in benign nevi. To assess the use of TPMs as an ancillary diagnostic tool, we report the concordance of the TPM status with the final diagnosis in clinical cases with distinct differential diagnostic scenarios: dysplastic nevus versus melanoma, atypical Spitz nevus versus melanoma, atypical deep penetrating nevus (DPN) versus melanoma, and atypical blue nevus versus malignant blue nevus. In a control cohort, we found a positive TPM in 51/70 (73%) of the total melanomas with the highest frequency in vertical growth phase melanoma cases. Conversely, only 2/35 (6%) dysplastic nevi in our control cases were TPM-positive and b were severely atypical dysplastic nevi. Our clinical cohort of 257 cases had a positive TPM in 24% of cases diagnosed as melanoma and in 1% of cases with a benign diagnosis. The overall concordance of the TPM status with the final diagnosis was 86%. The TPM status had the greatest concordance (95%) with the final diagnosis in the atypical DPN versus melanoma group, with the rest of the groups ranging between 50% and 88%. Overall, our results suggest that TPMs are most useful in the differential diagnosis of atypical DPN versus melanoma. It also has some value in the differential diagnosis of atypical Spitz tumor versus melanoma and dysplastic nevus versus melanoma, whereas in our cohort, it did not contribute meaningfully to differentiating malignant blue nevus and atypical blue nevus.

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.

An Atypical Deep Penetrating Nevus With Mutations in Beta Catenin, BRAFV600E, and IDH1R132C in an 8-Year-Old Boy

ABSTRACT

Deep penetrating nevus (DPN) is a pigmented melanocytic tumor which typically displays a wedge-shaped deep penetrating architecture. Some cases show a coexisting component resembling conventional melanocytic nevus. These morphological attributes are correlated with the acquisition of genomic alterations in the Wnt pathway on a background of underlying activating MAPK pathway mutations. Lesions with features of DPN, but displaying expansile architecture, sheet-like arrangement of cells, cytological atypia, and/or more than rare mitotic activity have been described as "atypical deep penetrating nevus" or "deep penetrating melanocytoma." The molecular correlates of these atypical morphological features are not well-established. In this case report, we describe a tumor in an 8-year-old boy with histological features of atypical DPN showing somatic BRAFV600E, beta catenin, and IDH1R132C mutations. The combination of abnormalities in MAPK and Wnt pathways with IDH1 mutations seems to be a reproducible feature in a subset of atypical DPNs. Whether this "three-hit" combination is associated with a significant risk of adverse outcome remains to be established.