Agminated Spitz naevus with an activating HRAS Q61R mutation

A Retrospective Analysis of Ambiguous Spitz Tumors Using Next-Generation Sequencing

Background: Spitz tumors (STs) are a diverse group of melanocytic lesions that range from benign to malignant. STs pose significant classification challenges due to overlapping histological and immunohistochemical (IHC) features among the STs with different malignant potential. This study aimed to assess the diagnostic value of a melanoma-specific next-generation sequencing (NGS) panel (MelArray) combined with IHC analysis to improve the assessment of diagnostically challenging ST cases. Methods: Patients with STs and available MelArray results were included in this retrospective analysis. Molecular analysis (genetic alterations, tumor mutational burden (TMB), and copy number variations (CNV)), clinical data (demographics and clinical course), and IHC data (scores for markers such as p16, Ki-67, HMB45, PRAME, and Melan A) were evaluated in conjunction and correlated with patient outcomes. Results: Atypical Spitz tumors (ASTs, n = 20) predominantly exhibited heterozygous deletions in melanoma-relevant genes, but these were not accompanied by the multiple damaging mutations commonly associated with melanoma. IHC scores were higher in ASTs compared to Spitz nevi (SN, n = 3), suggesting an intermediate biologic potential. SN exhibited minimal genetic alterations and low IHC scores, reflecting a benign profile. Genetic analysis of the Spitz melanoma (SM, n = 1) revealed a distinct molecular profile with damaging mutations affecting the key regulatory pathways involved in tumor progression, along with a high TMB, and an IHC score comparable to ASTs. During a median follow-up of 36 months (range: 6-48 months, n = 23), no recurrences, distant metastases, or tumor-related deaths were observed. Conclusions: The integration of NGS analysis with the MelArray panel, histology, and immunohistochemistry, enhances the diagnostic accuracy of challenging STs by identifying the genetic alterations linked to malignancy risk. This aids in the detection of high-risk lesions that need a more detailed work-up and more stringent follow-up, and those that will follow a benign course. Larger studies are needed to validate the clinical utility and broader applicability.

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.

[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.

Diagnostic Imaging of Agminated Blue Lesions and Blue Lesions with Satellitosis: Case Series with a Concise Review of the Current Literature

Background: Agmination and/or satellitosis in pigmented blue lesions is a phenomenon rarely mentioned in the literature and not well known. This phenomenon can be expressed by several benign and malignant pigmented blue lesions, such as blue nevi, Spitz nevi, melanocytoma and melanoma. On this spectrum, dermoscopy, reflectance confocal microscopy (RCM) and dynamic Optical coherence tomography (D-OCT) represent non-invasive imaging technologies, which may help clinicians in the diagnosis of melanoma and non-melanoma skin cancers in daily clinical practice. Methods: Currently, in the literature there is a lack of new data about agminated blue lesions and blues lesions with satellitosis, as well as the lack of a recent and updated review of the literature about this topic. Therefore, considering that clinicians must be confident with the diagnosis of these rare skin lesions, we decided to carry out this work. Results: In this paper, four new cases of agminated pigmented cutaneous lesions were described. Moreover, a review of the current literature on this topic was performed. Conclusions: A clinical-pathological correlation is often needed to reach a correct diagnosis; currently, dermoscopy and non-invasive diagnostic techniques, such as reflectance confocal microscopy and optical coherence tomography, due to the depth of these skin lesions in the dermis, can only make a partial and limited contribution.

Agminated presentation of fusion-driven melanocytic neoplasms

BACKGROUND

The conventionally understood pathogenesis of agminated Spitz nevi includes a mosaic HRAS mutation followed by copy number gains in 11p. However, we have recently observed agminated presentations of fusion-driven melanocytic neoplasms.

METHODS

We retrieved cases from our database of benign fusion-induced melanocytic neoplasms with an agminated presentation. Both the primary lesion and the secondary lesion were sequenced. TERT-promoter mutational testing and the melanoma fluorescence in situ hybridization assay were also performed.

RESULTS

Three cases were included. Two had a PRKCA fusion (partners ATP2B4 and MPZL1) and one had a ZCCHC8::ROS1 fusion. None of the cases met morphologic or molecular criteria for malignancy. There was no evidence of tumor progression in secondary lesions. The same fusion was identified in the primary and secondary lesions. None of the patients developed evidence of nodal or systemic metastasis.

CONCLUSIONS

We present accumulating evidence that fusion-driven melanocytic neoplasms can present with an agminated presentation. The differential diagnosis of an agminated presentation versus a locally recurrent or potentially locally metastatic tumor is critical, and accurate diagnosis has significant prognostic and therapeutic consequences for the patient. As with HRAS mutations, fusion-driven melanocytic tumors may have an agminated presentation.

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.