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

Gene Expression Profile of Benign, Intermediate, and Malignant Spitz and Spitzoid Melanocytic Lesions

Spitz and Spitzoid lesions represent one of the most challenging melanocytic neoplasms in dermatopathology. Nosologic classification has been more recently improved by the discovery of novel molecular drivers, particularly translocations. In the current study, we aimed to use an unbiased approach to explore the gene expression profile of a group of melanocytic Spitz and Spitzoid melanocytic lesions ranging from benign lesions to melanoma, including intermediate lesions such as SPARK nevi and atypical Spitz tumors/melanocytomas. Using unsupervised analysis of gene expression data, we found some distinct hierarchical clusters of lesions, including groups characterized by ALK and NTRK translocations. Few non-ALK translocated tumors demonstrated increased ALK expression, confirmed by immunohistochemistry. Spitz tumors with overlapping features of dysplastic nevi, so-called SPARK nevi, appear to have a common gene expression profile by hierarchical clustering. Finally, weighted gene correlation network analysis identified gene modules variably regulated in subtypes of these cases. Thus, gene expression profiling of Spitz and Spitzoid lesions represents a viable instrument for the characterization of these lesions.

Clinical, Morphologic, and Molecular Features of MAP3K8 Rearranged Spitz Neoplasms: A Retrospective Study Documenting That Bonafide Spitz Melanomas Are Rare

Previous studies regarding the clinical behavior of Spitz neoplasms lack genomic characterization. We aim to assess our hypothesis that most MAP3K8 Spitz neoplasms are indolent despite MAP3K8 being the single most common driver of Spitz melanoma. Further, we aim to identify genomic features associated with aggressive behavior and to better characterize the morphology of these cases. We analyzed the outcomes of MAP3K8 Spitz neoplasms. We also performed a meta-analysis of the outcomes of MAP3K8 Spitz from the literature. Morphologic features were compared with other variants of Spitz using a Student t test and χ 2 test. Two of 35 cases resulted in local recurrence and one of these cases had local regional metastasis; all other cases had no evidence of recurrence (mean follow-up time: 33 mo). MAP3K8 Spitz only rarely results in aggressive behavior. Metastatic cases have genomic mutations associated with tumor progression. Morphologically, MAP3K8 Spitz neoplasms frequently showed nodular silhouette, large cell size, epithelioid morphology, and severe nuclear atypia resulting in more frequent diagnosis as Spitz melanoma. Most MAP3K8 Spitz neoplasms have excellent prognoses, apart from rare cases harboring additional genomic abnormalities associated with tumor progression.

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.

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.

[Clinical, histological and genetic correlations in melanocytic tumours with chromosomal rearrangements]

In some tumoral subtypes chromosomal translocations lead to an oncogenic chimeric protein acting as a tumorigenesis driver event. The main fusion model combines the promoter swapping of an inactivated tumor suppressor gene and a functional kinase that evades its regulatory system. The range of described fusions keeps growing in the 2023 WHO classification of melanocytic tumours. It is not limited to the group of Spitz tumours as previously but now extends to blue tumours and dermal tumours with a melanocytic phenotype. Molecular pathology helps detect these anomalies using clinical and morphological features. This analysis is essential as this strongly conditions the adapted local treatment of such tumours who are often overtreated.

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 Tumor With SQSTM1::NTRK2 Fusion: A Clinicopathological Study of 5 Cases

ABSTRACT

Spitz tumors are melanocytic neoplasms characterized by specific, mutually exclusive driver molecular events, namely genomic rearrangements involving the threonine kinase BRAF and the tyrosine kinase receptors ALK , NTRK1 , NTRK2 , NTRK3 , MET , RET , ROS1 , and MAP3K8 or less commonly, mutations in HRAS or MAP2K1 . We hereby report 5 Spitz tumors with a SQSTM1::NTRK2 fusion. All patients were woman with the ages at diagnosis ranging from 30 to 50 years. Locations included the lower extremity (n = 3), forearm, and back (one each). All the neoplasms were superficial melanocytic proliferation with a flat to dome-shaped silhouette, in which junctional spindled and polygonal dendritic melanocytes were mainly arranged as horizontal nests associated with conspicuous lentiginous involvement of the follicular epithelium. Only one case showed heavily pigmented, vertically oriented melanocytic nests resembling Reed nevus. A superficial intradermal component observed in 2 cases appeared as small nests with a back-to-back configuration. In all lesions, next-generation sequencing analysis identified a SQSTM1::NTRK2 fusion. A single case studied with fluorescence in situ hybridization for copy number changes in melanoma-related genes proved negative. No further molecular alterations were detected, including TERT-p hotspot mutations.

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.

RASGRF1-rearranged Cutaneous Melanocytic Neoplasms With Spitzoid Cytomorphology: A Clinicopathologic and Genetic Study of 3 Cases

Spitz neoplasms, according to 2018 WHO Blue Book, are morphologically defined by spindled and/or epithelioid melanocytes and genetically by either HRAS mutations or kinase gene fusions. The terminology "spitzoid" refers to lesions with similar morphology but with alternate or undefined genetic anomalies. Herein, we present 3 melanocytic neoplasms with a spitzoid cytomorphology, variable nuclear atypia, and harboring undescribed fusions involving RASGRF1. Two cases presented as unpigmented papules on the heel of a 26-year-old female (case 1) and the forearm of a 13-year-old boy (case 2). They were classified as low-grade melanocytomas (WHO 2018). The third case appeared as a pigmented ulcer on the sole of a 72-year-old female (case 3) that displayed diagnostic features of an invasive melanoma (Breslow thickness 6 mm, Clark level V). A wide skin reexcision identified an epidermotropic metastasis, and sentinel lymph node biopsy displayed multiple subcapsular metastatic deposits. RNA sequencing revealed CD63::RASGRF1, EHBP1::RASGRF1, and ABCC2::RASGRF1 fusions in cases 1 to 3, respectively. They were confirmed by a RASGRF1 break-apart fluorescence in situ hybridization technique. Translocations of RASGRF1, a gene coding a guanine nucleotide exchange factor but not a kinase, have rarely been reported in tumors. While all these cases showed spitzoid cytomorphology, it is too early to tell if they are true Spitz neoplasms as currently defined.

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.

Detection of NTRK Fusions and TRK Expression and Performance of pan-TRK Immunohistochemistry in Routine Diagnostics: Results from a Nationwide Community-Based Cohort

Gene fusions involving NTRK1, NTRK2, and NTRK3 are rare drivers of cancer that can be targeted with histology-agnostic inhibitors. This study aimed to determine the nationwide landscape of NTRK/TRK testing in the Netherlands and the usage of pan-TRK immunohistochemistry (IHC) as a preselection tool to detect NTRK fusions. All pathology reports in 2017–2020 containing the search term ‘TRK’ were retrieved from the Dutch Pathology Registry (PALGA). Patient characteristics, tumor histology, NTRK/TRK testing methods, and reported results were extracted. NTRK/TRK testing was reported for 7457 tumors. Absolute testing rates increased from 815 (2017) to 3380 (2020). Tumors were tested with DNA/RNA-based molecular assay(s) (48%), IHC (47%), or in combination (5%). A total of 69 fusions involving NTRK1 (n = 22), NTRK2 (n = 6) and NTRK3 (n = 41) were identified in tumors from adult (n = 51) and pediatric (n = 18) patients. In patients tested with both IHC and a molecular assay (n = 327, of which 29 NTRK fusion-positive), pan-TRK IHC had a sensitivity of 77% (95% confidence interval (CI), 56–91) and a specificity of 84% (95% CI, 78–88%). These results showed that pan-TRK IHC has a low sensitivity in current routine practice and warrants the introduction of quality guidelines regarding the implementation and interpretation of pan-TRK IHC.

Wholistic approach - transcriptomic analysis and beyond using archival material for molecular diagnosis

Many neoplasms remain unclassified after histopathological examination, which requires further molecular analysis. To this regard, mesenchymal neoplasms are particularly challenging due to the combination of their rarity and the large number of subtypes, and many entities still lack robust diagnostic hallmarks. RNA transcriptomic profiles have proven to be a reliable basis for the classification of previously unclassified tumors and notably for mesenchymal neoplasms. Using exome-based RNA capture sequencing on more than 5000 samples of archival material (FFPE), the combination of expression profiles analyzes (including several clustering methods), fusion genes, and small nucleotide variations has been developed at the Centre Léon Bérard (CLB) in Lyon for the molecular diagnosis of challenging neoplasms and the discovery of new entities. The molecular basis of the technique, the protocol, and the bioinformatics algorithms used are described herein, as well as its advantages and limitations.

Cutaneous Melanomas Arising during Childhood: An Overview of the Main Entities

Cutaneous melanomas are exceptional in children and represent a variety of clinical situations, each with a different prognosis. In congenital nevi, the risk of transformation is correlated with the size of the nevus. The most frequent type is lateral transformation, extremely rare before puberty, reminiscent of a superficial spreading melanoma (SSM) ex-nevus. Deep nodular transformation is much rarer, can occur before puberty, and must be distinguished from benign proliferative nodules. Superficial spreading melanoma can also arise within small nevi, which were not visible at birth, usually after puberty, and can reveal a cancer predisposition syndrome (CDKN2A or CDK4 germline mutations). Prognosis is correlated with classical histoprognostic features (mainly Breslow thickness). Spitz tumors are frequent in adolescents and encompass benign (Spitz nevus), intermediate (atypical Spitz tumor), and malignant forms (malignant Spitz tumor). The whole spectrum is characterized by specific morphology with spindled and epithelioid cells, genetic features, and an overall favorable outcome even if a regional lymph node is involved. Nevoid melanomas are rare and difficult to diagnose clinically and histologically. They can arise in late adolescence. Their prognosis is currently not very well ascertained. A small group of melanomas remains unclassified after histological and molecular assessment.