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

Nevi - when to refer

PURPOSE OF REVIEW

Congenital melanocytic nevi (CMN) and acquired nevi are prevalent in pediatric populations, with distinct characteristics and management considerations. This chapter aims to equip pediatricians with knowledge to discern between benign and high-risk nevi, facilitating appropriate referrals and management within primary care settings. Risk factors associated with malignant melanoma (MM) underscore the importance of vigilant monitoring and early referral to dermatology for suspicious lesions.

RECENT FINDINGS

Recent findings highlight the variability in CMN presentation and the evolving diagnostic strategies, emphasizing the need for multidisciplinary approaches to optimize patient outcomes.

SUMMARY

Management of CMN involves tailored surveillance and intervention strategies, with an emphasis on early identification of high-risk features for MM and neurocutaneous melanosis (NCM). Pediatricians play a crucial role in advocating for sun protection practices and facilitating timely referrals, thereby contributing to the overall well being of pediatric patients with nevi.

The Impact of Next-generation Sequencing on Interobserver Agreement and Diagnostic Accuracy of Desmoplastic Melanocytic Neoplasms

Next-generation sequencing (NGS) is increasingly being utilized as an ancillary tool for diagnostically challenging melanocytic neoplasms. It is incumbent upon the pathology community to perform studies assessing the benefits and limitations of these tools in specific diagnostic scenarios. One of the most challenging diagnostic scenarios faced by skin pathologists involves accurate diagnosis of desmoplastic melanocytic neoplasms (DMNs). In this study, 20 expert melanoma pathologists rendered a diagnosis on 47 DMNs based on hematoxylin and eosin sections with demographic information. After submitting their diagnosis, the experts were given the same cases, but this time with comprehensive genomic sequencing results, and asked to render a diagnosis again. Identification of desmoplastic melanoma (DM) improved by 7%, and this difference was statistically significant ( P <0.05). In addition, among the 15 melanoma cases, in the pregenomic assessment, only 12 were favored to be DM by the experts, while after genomics, this improved to 14 of the cases being favored to be DM. In fact, some cases resulting in metastatic disease had a substantial increase in the number of experts recognizing them as DM after genomics. The impact of the genomic findings was less dramatic among benign and intermediate-grade desmoplastic tumors (BIDTs). Interobserver agreement also improved, with the Fleiss multirater Kappa being 0.36 before genomics to 0.4 after genomics. NGS has the potential to improve diagnostic accuracy in the assessment of desmoplastic melanocytic tumors. The degree of improvement will be most substantial among pathologists with some background and experience in bioinformatics and melanoma genetics.

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.

A pilot study of p53 immunohistochemistry in atypical squamous lesions, using a vulvar scoring system

BACKGROUND

Histopathologic overlap between cutaneous squamous cell carcinoma (cSCC) and its indolent mimics likely leads to the overdiagnosis of cSCC.

OBJECTIVE

To perform a pilot study of the p53 immunohistochemical scoring system developed on vulvar squamous lesions in cSCC.

METHODS

The consistency and reliability of p53 immunostaining using a scoring system developed on vulvar cases, as compared with TP53 genomic sequencing, was studied in an initial cohort of 28 cutaneous cases. p53 labeling was further assessed in an additional 63 cases of atypical squamous lesions, including 20 atypical squamous lesions classified by the authors as benign, 22 cases diagnosed as cSCC without high-risk features, and 21 cases of high-risk cSCC (cSCC-HR).

RESULTS

The concordance of p53 labeling and TP53 sequencing was 82.1%. Four positive patterns of p53 mutation were identified: basal, parabasal/diffuse, null, and cytoplasmic. p53 positivity in atypical, benign squamous lesions (10%) was significantly lower than that of low-risk cSCC (63.6%, p = 0.0004) or cSCC-HR (90.5%, p < 0.0001). p53 positivity in low-risk cSCC versus cSCC-HR was not statistically significant (p = 0.07).

CONCLUSION

p53 Labeling may be a helpful biomarker to support the diagnosis of cSCC and distinguish cSCC from atypical but benign mimics.

Mosaic RASopathies concept: different skin lesions, same systemic manifestations?

BACKGROUND

Cutaneous epidermal nevi are genotypically diverse mosaic disorders. Pathogenic hotspot variants in HRAS, KRAS, and less frequently, NRAS and BRAF may cause isolated keratinocytic epidermal nevi and sebaceous nevi or several different syndromes when associated with extracutaneous anomalies. Therefore, some authors suggest the concept of mosaic RASopathies to group these different disorders.

METHODS

In this paper, we describe three new cases of syndromic epidermal nevi caused by mosaic HRAS variants: one associating an extensive keratinocytic epidermal nevus with hypomastia, another with extensive mucosal involvement and a third combining a small sebaceous nevus with seizures and intellectual deficiency. Moreover, we performed extensive literature of all cases of syndromic epidermal nevi and related disorders with confirmed pathogenic postzygotic variants in HRAS, KRAS, NRAS or BRAF.

RESULTS

Most patients presented with bone, ophthalmological or neurological anomalies. Rhabdomyosarcoma, urothelial cell carcinoma and pubertas praecox are also repeatedly reported. KRAS pathogenic variants are involved in 50% of the cases, especially in sebaceous nevi, oculoectodermal syndrome and encephalocraniocutaneous lipomatosis. They are frequently associated with eye and brain anomalies. Pathogenic variants in HRAS are rather present in syndromic keratinocytic epidermal nevi and phacomatosis pigmentokeratotica.

CONCLUSION

This review delineates genotype/phenotype correlations of syndromic epidermal nevi with somatic RAS and BRAF pathogenic variants and may help improve their follow-up.

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.

Pediatric Atypical Melanocytic Proliferations: Single-Site Retrospective Cohort Assessment of Treatment and Long-Term Follow-Up

Atypical and malignant cutaneous tumors are understudied in the pediatric population, with limited data on long-term follow-up. This study examines pediatric (0-18 years) atypical melanocytic proliferations over a twenty-year period (January 2002-December2022) using the EPIC SlicerDicer at our institution. Over a twenty-year period, there were 55 cases of pediatric melanoma (53 patients). The median follow-up time was 8 years, 11 months. A proportion of 96% were treated with wide local excision (WLE), and 47% had a sentinel lymph node biopsy (SLNB) (35% positive rate). There were 101 atypical Spitz tumor cases (85% atypical Spitz tumors, 15% Spitz melanoma), with a median follow-up duration of 9 years. A proportion of 77% were treated with WLE (with one patient dying of metastatic disease). There were 10 cases of atypical melanocytic proliferations not otherwise specified, including 5 pigmented epithelioid melanocytomas (PEM), 4 deep-penetrating nevi, and 1 atypical cellular blue nevus. This study adds to the growing body of knowledge on pediatric atypical cutaneous melanocytic proliferations, aligning with many described characteristics such as disease location and overall survival rates, with distinct exceptions (higher melanoma positive SLNB rate, lower atypical Spitz tumor WLE rate, and a case of fatal metastatic atypical Spitz tumor).

A Spitzoid Tumor dataset with clinical metadata and Whole Slide Images for Deep Learning models

Spitzoid tumors (ST) are a group of melanocytic tumors of high diagnostic complexity. Since 1948, when Sophie Spitz first described them, the diagnostic uncertainty remains until now, especially in the intermediate category known as Spitz tumor of unknown malignant potential (STUMP) or atypical Spitz tumor. Studies developing deep learning (DL) models to diagnose melanocytic tumors using whole slide imaging (WSI) are scarce, and few used ST for analysis, excluding STUMP. To address this gap, we introduce SOPHIE: the first ST dataset with WSIs, including labels as benign, malignant, and atypical tumors, along with the clinical information of each patient. Additionally, we explain two DL models implemented as validation examples using this database.

Paediatric Spitzoid Neoplasms: 10-Year Retrospective Study Characterizing Histological, Clinical, Dermoscopic Presentation and FISH Test Results

INTRODUCTION

Spitzoid lesions are a wide tumour class comprising Spitz nevus (SN), atypical Spitz tumour (AST) and Spitz melanoma (SM).

MATERIALS AND METHODS

We conducted a single-centre-based retrospective survey on all histologically diagnosed spitzoid lesions of paediatric patients (1-18 years) of the last 10 years (2012-2022). Histopathological reports and electronic records of patients were used to retrieve relevant data regarding patients' features, clinical and dermatoscopical aspects of lesions when recorded, and FISH tests when present.

RESULTS

Of 255 lesions, 82% were histologically benign, 17% atypical, 1% malignant. Clinically, 100% of SM were large (≥6 mm) and raised; AST were mainly large (63%), raised (98%), pink (95%). Small (≤5 mm), pigmented, flat lesions correlated with benign histology (respectively 90%, 97%, 98% SN) (p < 0.0001). Dermatoscopical patterns were analysed in 100 patients: starburst pattern correlated with benign histology (26% SN (p = 0.004)), while multicomponent pattern correlated with atypical/malignant lesions (56% AST, 50% SM (p = 0.0052)). Eighty-five lesions were subjected to fluorescence in situ hybridization (FISH): 34 (71% AST; 29% SN) were FISH-positive; 51 (63% SN; 37% AST) were FISH-negative (p = 0.0038).

DISCUSSION

This study confirmed predominant benign histology (82%) of paediatric spitzoid lesions, thus detecting 17% AST and 1% SM, highlighting the need for caution in handling spitzoid lesions.

CONCLUSION

Until AST are considered potentially malignant proliferations and no reliable criteria are identified to distinguish them, the authors suggest a prudent approach, especially in children.

Modern Concepts in Melanocytic Tumors

The advent of molecular pathology has fueled unprecedented advances in the diagnosis and understanding of melanocytic tumors. These advances, however, have also generated concepts that may be difficult to grasp for clinical practitioners, who are not always conversant with the array of genetic techniques employed in the laboratory. These same practitioners, however, are being increasingly called on to provide treatments that are often based on the latest molecular findings for melanocytic tumors. We review the most recent concepts in the pathway classification of melanocytic tumors, including intermediate lesions known as melanocytomas. We examine the genetic and molecular techniques used to study these tumors, look at where they overlap, and discuss their limitations and some of the most difficult-to-interpret results.