Molecular cytogenetic analysis of Spitz nevi shows clear differences to melanoma

Spitzoid melanoma of the finger: a case report

BACKGROUND

Melanoma is the most malignant skin tumor, with a high metastatic potential. Spitzoid melanoma is a subtype of melanoma requiring rapid management and extensive tumor resection. We have set the goal to recognize anatomical peculiarities and difficulties diagnoses posed by this type of tumor, as well as to recognize the management modalities, especially the surgical one, of malignant spitzoid melanoma.

CASE PRESENTATION

A 25-year-old Tunisian male patient had consulted for nodular lesion of the right index, evolving for 4 years. A malignant tumor was strongly suspected, then confirmed as a melanoma by a biopsy excision. Initially, the excision was incomplete in depth, suggesting a complementary surgery, but the patient refused it; 3 years later, the patient again consulted after the appearance of an axillary lymphadenopathy and worsening of the skin lesion. A supplement of tumor removal with lymph node biopsy were performed. It was decided to perform an amputation of the second ray and the first commissure with cheiroplasty, reconstructing a four-finger hand. An homolateral axillary cleaning was performed at the same time. The postoperative result is considered esthetically and functionally satisfying. The evolution was marked by the appearance of pulmonary metastases, requiring adjuvant chemotherapy. A regression of the nodule under the mammary skin and total disappearance of axillary nodes have been marked; but the patient's condition rapidly deteriorated, and he died after a 2-month decline.

CONCLUSION

Spitzoid melanoma is exceptional, posing difficulties in diagnostics, and it should not be underestimated, considering that it may involve the vital prognosis. Knowledge of this rare form of melanoma is important to avoid misdiagnosis, which delays diagnosis and subsequent therapy.

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.

Ancillary testing for melanoma: current trends and practical considerations

The diagnosis of melanocytic lesions is aided by ancillary testing, but clinical inspection with the histomorphological assessment on biopsy remains sufficient in most cases. Immunohistochemistry and molecular studies have proven useful for diminishing the pool of histomorphologically borderline lesions, and sequential testing may further improve overall diagnostic performance, but these assays should be used in a stepwise fashion if at all. Ancillary tests vary based on their technology, performance, and practical considerations, including but not limited to the specific diagnostic question, cost, and turn-around time, which impact test selection. This review examines currently used ancillary tests for the purpose of characterizing melanocytic lesions. Both scientific and practical considerations are discussed.

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.

Molecular testing in melanoma for the surgical pathologist

The diagnostic work-up of melanocytic tumours has undergone significant changes in the last years following the exponential growth of molecular assays. For the practising pathologist it is often difficult to sort through the multitude of different tests that are currently available for clinical use. The molecular tests used in melanocytic pathology can be broadly divided into four categories: (1) tests that predict response to systemic therapy in melanoma; (2) tests that predict prognosis in melanoma; (3) tests useful in determining the type or class of melanocytic tumour; and (4) tests useful in the differential diagnosis of naevus versus melanoma (primarily used as an aid in the diagnosis of histologically ambiguous melanocytic lesions). This review will present an updated synopsis of major molecular ancillary tests used in clinical practice.

PRAME Expression Correlates With Genomic Aberration and Malignant Diagnosis of Spitzoid Melanocytic Neoplasms

ABSTRACT

Spitzoid melanocytic neoplasms are a diagnostically challenging class of lesions in dermatopathology. Recently, molecular assays and immunohistochemical markers have been explored as ancillary methods to assist in the diagnostic workup. Specifically, preferentially expressed antigen in melanoma (PRAME) immunohistochemistry is a nuclear stain commonly positive in melanomas, but not in nevi. This study investigates PRAME immunoreactivity (≥75% positive nuclear staining in tumor cells) in a set of 59 spitzoid melanocytic neoplasms with known clinical outcomes. We compared PRAME status with (1) the clinical outcomes, (2) the morphologic diagnoses, and (3) the status of TERT promoter mutation. Regarding clinical outcomes, 3 cases developed metastatic disease, of which 2 expressed diffusely positive PRAME staining. Of the 56 cases that did not show evidence of metastasis, 6 expressed diffusely positive PRAME staining. Morphologically, diffusely positive PRAME staining was seen in 7 of 21 cases (33.3%) diagnosed as melanoma and only 1 benign tumor 1 of 38 (2.6%). There were 4 of 8 cases with a TERT promoter mutation which were diffusely PRAME-positive compared with 4 of 51 cases without TERT promoter mutation ( P = 0.001). Our results show a statistically significant correlation between PRAME expression and the diagnosis, outcome, and TERT promoter mutation status of atypical spitzoid melanocytic neoplasms, suggesting immunohistochemistry for PRAME can help support a suspected diagnosis. However, because of occasional false-positive and negative test results, correlation with the clinical and histologic findings as well as results from other tests is needed for the interpretation of diagnostically challenging spitzoid melanocytic neoplasms.

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.

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.

Diagnostic and prognostic classification of atypical spitzoid tumours based on histology and genomic aberrations: A prospective cohort study with long-term follow-up

BACKGROUND

Histological classification of atypical spitzoid tumours (ASTs) is unreliable, and categorisation of these lesions into benign and malignant is poorly reproducible. Here, we classified ASTs based on histology and chromosomal aberrations and explored the prognostic significance of genomic aberrations in a prospective cohort with a long-term follow-up.

PATIENTS AND METHODS

Histologically equivocal ASTs from 76 patients were analysed by array comparative genomic hybridisation (aCGH). Tumours were histologically assessed by a panel of dermatopathologist before and after aCGH and classified as benign, ambiguous or malignant. Chromosomal aberrations were correlated with an outcome.

RESULTS

Chromosomal aberrations were detected in 45 (59%) of 76 ASTs (median age: 16 years, range: 0-74; median follow-up: 90 months, range: 13-153). The initial histological diagnosis was changed upon presentation of aCGH results in 36 of 76 cases (47%). The final diagnostic interpretation classified 61% of the lesions as benign, 18% as ambiguous and 21% as malignant. Positive sentinel lymph node biopsies (6+/29) occurred at similar rates in all diagnostic groups (P = 0.83) and were not associated with an unfavourable outcome. Two patients had local recurrences, but none of the patients developed metastasis beyond the sentinel lymph node.

CONCLUSIONS

All ASTs had an excellent prognosis, even in cases with worrisome morphology and chromosomal aberrations. With no distant metastasis or death in long-term follow-up of 76 patients, no correlation between chromosomal aberrations and prognosis was possible. However, it seems likely that in larger cohorts, metastases would arise in cases with complex aberrations and these patients should undergo clinical follow-up.

ROS-1 Pattern Of Immunostaining In 11 Cases Of Spitzoid Tumours: Comparison With Histopathological, Fish And Ngs Analysis

AIMS

Spitzoid tumours have been shown to harbour exclusive kinase fusions. Few studies have analysed substantial numbers of ROS-1 rearranged lesions, particularly immunohistochemistry has been poorly investigated.

METHODS AND RESULTS

Among a group of 35 spitzoid tumours, of which 34 consecutively diagnosed in a 3-year period, we found 11 cases ROS-1 positive at immunohistochemistry, belonging to 10 patients, 8 females and 2 males, aged 3 to 52 years (median 29); most lesions (8) were localized on the lower extremities. Four patterns of immunostaining were observed: cytoplasmic granular diffuse (6 cases), sparse cytoplasmic granules (3), paranuclear dots (1), and nuclear (1). All cases resulted rearranged at FISH analysis (cut-off >15%). NGS-RNA analysis featured specific fusions of ROS-1 in 4 cases: two with PWWP2A, one with PPFIBP1, and one with ZCCHC8. NGS-DNA analysis demonstrated in 5 cases specific mutations of AKT, EGFR, NRAS, MYC, ALK, and KIT genes. ROS-1 lesions belonged predominantly to the "Atypical Spitz Tumour" group and featured mainly a nested pattern at histology. Interestingly, one patient developed two lesions ROS-1 positive.

CONCLUSIONS

Immunohistochemistry showed a 100% of sensitivity and specificity compared to FISH results, corresponding to ROS-1 rearrangement in 31% of cases studied. These observations shed new light on the value of immunohistochemical evaluation of ROS-1 in spitzoid tumours. ROS-1 patterns of immunostaining probably reflect different subcellular localizations of ROS-1 fusions, although no specific correlations were found in cases studied. Immunohistochemistry and FISH resulted the most sensitive techniques in detecting ROS-1 rearrangement in this subset of neoplasms.

A prospective, comprehensive registry that integrates the molecular analysis of pediatric and adolescent melanocytic lesions

BACKGROUND

Childhood melanocytic tumors represent a diagnostic and therapeutic challenge, and additional research is needed to better define the natural history of these tumors.

METHODS

The authors developed a comprehensive, prospective registry called Molecular Analysis of Childhood Melanocytic Tumors for children and adolescents with an atypical Spitz tumor/Spitz melanoma (AST/SM), conventional or adult-type melanoma (CM), melanoma arising in a giant congenital nevus (MCM), or atypical melanocytic proliferation of other types (OT) to better define the clinical behavior of these lesions by incorporating an integrated clinicopathologic and molecular analysis using centralized pathology review and various platforms, including fluorescence in situ hybridization; array comparative genomic hybridization; and whole genome, exome, and capture targeted panels.

RESULTS

From May 2016 to November 2019, 70 children were enrolled with a median age at diagnosis of 9.1 years. Thirty-seven had AST/SM, 17 had CM, 4 had MCM, and 12 had OT. Patients with AST/SM were younger (median age, 7 years), and their tumor most commonly arose in the extremities and trunk. The most common gene rearrangements included MAP3K8 and ALK. None of the 33 patients who underwent a TERT promoter mutation analysis had a mutation, and all patients were alive. Among the CM patients, the median age was 13 years; 11 had a BRAFV600E mutation, and 7 had a TERT promoter mutation. Three patients died of their disease. All 4 patients with MCM harbored an NRASQ61 mutation and died of their disease. The OT group was heterogenous, and all patients survived.

CONCLUSIONS

The incorporation of an integrated clinicopathologic and genomic analysis identifies distinct subgroups of pediatric melanocytic lesions that have different clinical behaviors. The integration of this combined diagnostic modality can help to individualize diagnoses and treatments for these patients.

Expanding the Spectrum of Microscopic and Cytogenetic Findings Associated With Spitz Tumors With 11p Gains

A subset of Spitz tumors is associated with a copy number increase of chromosome 11p and activating mutations of HRAS. These aberrations have been reported to occur in association with desmoplastic Spitz nevi. Little is known to what extent 11p gains can also be found in nondesmoplastic tumors. To learn more about the spectrum of microscopic and cytogenetic changes that can be seen in Spitz lesions in association with 11p gains, we reviewed the clinical and pathologic features of 40 cases. Patient ages ranged from 3 to 75 years. The most common anatomic site was the head and neck region, followed by the upper extremities. Prominent desmoplasia was present in 10 cases. Seven tumors lacked significant stromal fibrosis. Twenty tumors were mitotically active. Novel microscopic features encountered in a few cases include a tumor with a polypoid silhouette and papillomatous surface and rare atypical tumors with a deep bulbous growth pattern. Among 36 cases analyzed by single-nucleotide polymorphism array or comparative genomic hybridization, 28 tumors had gains of the entire or near-entire p-arm of chromosome 11 with no other coexisting unbalanced genomic aberration. Eight cases had additional changes; 6 of these with 1 additional aberration per case, and 2 cases had several chromosomal aberrations. We also examined a subset of tumors by fluorescence in situ hybridization for the HRAS gene locus (11p15.5). All tumors were fluorescence in situ hybridization-positive. In conclusion, we expand the spectrum of pathologic findings associated with Spitz tumors with 11p gains. This cytogenetic aberration is not restricted to desmoplastic Spitz nevi. It can also be seen in nondesmoplastic and papillomatous lesions and atypical melanocytic tumors with a deep bulbous growth. We also document that in some Spitz tumors additional cytogenetic aberrations may be found, the significance of which remains to be determined.

Spitz Tumors With ROS1 Fusions: A Clinicopathological Study of 6 Cases, Including FISH for Chromosomal Copy Number Alterations and Mutation Analysis Using Next-Generation Sequencing

Spitz tumors represent a heterogeneous group of melanocytic neoplasms with a spectrum of biological behavior ranging from benign (Spitz nevus) to malignant (spitzoid melanoma). Prediction of the behavior of these lesions based on their histological presentation is not always possible. Recently, mutually exclusive activating kinase fusions, involving ALK, NTRK1, NTRK3, RET, MET, ROS1, and BRAF, have been found in a subset of spitzoid lesions. Some of these genetic alterations were associated with specific morphological features. Here, we report the histological presentation of 6 Spitz tumors with ROS1 fusion. The age of the patients ranged from 6 to 34 years, with strong female prevalence (5:1). All neoplasms were compound melanocytic proliferations with a predominant dermal growth but a conspicuous junctional component displaying atypical microscopic features qualifying them as atypical Spitz tumor. FIP1L1 and CAPRIN1 were identified as 2 novel 5'-fusion partners of ROS1 along with the known PWWP2A-ROS1 fusion. FISH for copy number changes of 9p21, 6p25, and 11q13 was negative in all but 1 neoplasm harboring isolated gain of 8q24. TERT-promoter hotspot mutation analysis was negative in all tumors. All patients are disease-free after a mean follow-up period of 30 months. It is concluded that ROS1-fused spitzoid neoplasms seem to have no distinctive histopathological features although consistent findings were spindled melanocytes arranged in confluent whorling nests, prominent transepidermal elimination of melanocytic nests, and myxoid/mucinous changes.

Mimics of melanoma in reflectance confocal microscopy

The diagnosis of melanoma is challenging for both dermatologists and oncologists. Incidence of melanoma increases at a rate of 3-7% per year. Usage of modern tools such as dermoscopy and in vivo reflectance confocal microscopy improve early diagnosis and can save a life. There are a few melanoma simulators which can cause confusion and mislead in the differential diagnosis. This study aims to present skin lesions which can be similar to melanoma in confocal microscopy and to emphasize the importance of a detailed differential diagnosis. We describe five melanocytic lesions similar to melanoma and misleading confocal features. Although in vivo reflectance confocal microscopy is very useful in differentiating melanocytic lesions, histopathology evaluation in cases of melanoma mimics is definitive.

A sixteen-year single-center retrospective chart review of Spitz nevi and spitzoid neoplasms in pediatric patients

BACKGROUND

Spitzoid neoplasms in pediatric patients pose an interesting challenge for clinicians. More data on the clinical, histologic, and molecular characteristics of these lesions are necessary to distinguish features that may portend recurrence or malignant behavior to help determine future treatment guidelines in pediatric patients.

METHODS

Institutional Review Board approval was obtained from Children's Hospital of Wisconsin to conduct a retrospective analysis of spitzoid neoplasms. Patients with biopsied or excised spitzoid neoplasms between 01/01/2000 and 08/01/2016 were included. Pertinent clinical and histologic data were collected. Atypical, unusual, or diagnostically uncertain lesions were selected for re-review.

RESULTS

266 lesions from 264 patients were included. 243 were classified as benign (91.35%), 22 as atypical (8.27%), and 1 as spitzoid melanoma (0.38%). No clinical or histologic variables were found to be statistically significant between the benign Spitz, atypical Spitz, and spitzoid melanoma cohorts. No known deaths occurred.

CONCLUSION

Our findings highlight the extreme variability of spitzoid neoplasms clinically and histologically. Importantly, this study demonstrates that the vast majority of spitzoid neoplasms in pediatric populations are benign and supports conservative management of spitzoid lesions in children.

A Clinicopathological Study of 29 Spitzoid Melanocytic Lesions With ALK Fusions, Including Novel Fusion Variants, Accompanied by Fluorescence In Situ Hybridization Analysis for Chromosomal Copy Number Changes, and Both TERT Promoter and Next-Generation Sequencing Mutation Analysis

ALK-fused spitzoid neoplasms represent a distinctive group of melanocytic lesions. To date, few studies addressed genetic and chromosomal alterations in these lesions beyond the ALK rearrangements. Our objective was to study genetic alterations, including ALK gene fusions, telomerase reverse transcriptase promoter (TERT-p) mutations, chromosomal copy number changes, and mutations in other genes. We investigated 29 cases of Spitz lesions (11 Spitz nevi and 18 atypical Spitz tumors), all of which were ALK immunopositive. There were 16 female and 13 male patients, with age ranging from 1 to 43 years (mean, 18.4 years). The most common location was the lower extremity. Microscopically, all neoplasms were polypoid or dome shaped with a plexiform, predominantly dermally located proliferation of fusiform to spindled melanocytes with mild to moderate pleomorphism. The break-apart test for ALK was positive in 17 of 19 studied cases. ALK fusions were detected in 23 of 26 analyzable cases by Archer FusionPlex Solid Tumor Kit. In addition to the previously described rearrangements, 3 novel fusions, namely, KANK1-ALK, MYO5A-ALK, and EEF2-ALK, were found. Fluorescence in situ hybridization for copy number changes yielded one case with the loss of RREB1 among 21 studied cases. TERT-p hotspot mutation was found in 1 of 23 lesions. The mutation analysis of 271 cancer-related genes using Human Comprehensive Cancer Panel was performed in 4 cases and identified in each case mutations in several genes with unknown significance, except for a pathogenic variant in the BLM gene. Our study confirms that most ALK fusion spitzoid neoplasms can be classified as atypical Spitz tumors, which occurs in young patients with acral predilection and extends the spectrum of ALK fusions in spitzoid lesions, including 3 hitherto unreported fusions. TERT-p mutations and chromosomal copy number changes involving 6p25 (RRB1), 11q13 (CCND1), 6p23 (MYB), 9p21 (CDKN2A), and 8q24 (MYC) are rare in these lesions. The significance of mutation in other genes remains unknown.

Non-BRAF Mutant Melanoma: Molecular Features and Therapeutical Implications

Melanoma is one of the most aggressive tumors of the skin, and its incidence is growing worldwide. Historically considered a drug resistant disease, since 2011 the therapeutic landscape of melanoma has radically changed. Indeed, the improved knowledge of the immune system and its interactions with the tumor, and the ever more thorough molecular characterization of the disease, has allowed the development of immunotherapy on the one hand, and molecular target therapies on the other. The increased availability of more performing technologies like Next-Generation Sequencing (NGS), and the availability of increasingly large genetic panels, allows the identification of several potential therapeutic targets. In light of this, numerous clinical and preclinical trials are ongoing, to identify new molecular targets. Here, we review the landscape of mutated non-BRAF skin melanoma, in light of recent data deriving from Whole-Exome Sequencing (WES) or Whole-Genome Sequencing (WGS) studies on melanoma cohorts for which information on the mutation rate of each gene was available, for a total of 10 NGS studies and 992 samples, focusing on available, or in experimentation, targeted therapies beyond those targeting mutated BRAF. Namely, we describe 33 established and candidate driver genes altered with frequency greater than 1.5%, and the current status of targeted therapy for each gene. Only 1.1% of the samples showed no coding mutations, whereas 30% showed at least one mutation in the RAS genes (mostly NRAS) and 70% showed mutations outside of the RAS genes, suggesting potential new roads for targeted therapy. Ongoing clinical trials are available for 33.3% of the most frequently altered genes.

Through the looking glass and what you find there: making sense of comparative genomic hybridization and fluorescence in situ hybridization for melanoma diagnosis

Melanoma is the leading cause of death among cutaneous neoplasms. Best outcome relies on early detection and accurate pathologic diagnosis. For the great majority of melanocytic tumors, histopathologic examination can reliably distinguish nevi from melanomas. However, there is a subset of melanocytic tumors that cannot be definitively classified as benign or malignant using histopathological criteria alone. These tumors are usually diagnosed using terms that imply various degrees of uncertainty in regards to their malignant potential and create the possibility for over or undertreatment. For such tumors, additional ancillary tests would be beneficial in adjudicating a more definitive diagnosis. In recent years, DNA-based molecular ancillary tests, specifically comparative genomic hybridization and fluorescence in situ hybridization, have been developed to help guide the diagnosis of ambiguous melanocytic proliferations. This study will present an updated overview of these two major ancillary tests, which are currently being used in clinical practice to assist in the diagnosis of challenging melanocytic neoplasms.

Histopathology-guided mass spectrometry differentiates benign nevi from malignant melanoma

PURPOSE

Distinguishing benign nevi from malignant melanoma using current histopathological criteria may be very challenging and is one the most difficult areas in dermatopathology. The goal of this study was to identify proteomic differences, which would more reliably differentiate between benign and malignant melanocytic lesions.

METHODS

We performed histolpathology - guided mass spectrometry (HGMS) profiling analysis on formalin-fixed, paraffin embedded tissue samples to identify differences at the proteomic level between different types of benign nevi and melanomas. A total of 756 cases, of which 357 cases of melanoma and 399 benign nevi, were included in the study. The specimens originated from both biopsies (376 samples) and tissue microarray (TMA) cores (380 samples). After obtaining mass spectra from each sample, classification models were built using a training set of biopsy specimens from 111 nevi and 100 melanomas. The classification algorithm developed on the training data set was validated on an independent set of 288 nevi and 257 melanomas from both biopsies and TMA cores.

RESULTS

In the melanoma cohort, 239/257 (93%) cases classified correctly in the validation set, 3/257 (1.2%) classified incorrectly, and 15/257 (5.8%) classified as indeterminate. In the cohort of nevi, 282/288 (98%) cases classified correctly, 1/288 (0.3%) classified incorrectly, and 5/288 (1.7%) were indeterminate. HGMS showed a sensitivity of 98.76% and specificity of 99.65% in determining benign vs malignant.

CONCLUSION

HGMS proteomic analysis is an objective and reliable test with minimal tissue requirements, which can be a helpful ancillary test in the diagnosis of challenging melanocytic lesions.

Spitz Nevus and Other Spitzoid Tumors in Children. Part 2: Cytogenetic and Molecular Features. Prognosis and Treatment

Melanocytic neoplasms with spitzoid morphology (Spitz nevi, atypical Spitz tumors, and spitzoid melanomas) may be benign or malignant. Because the malignant potential of atypical Spitz tumors is uncertain, the proper therapeutic approach has been much debated over the years. Promising new techniques for molecular analysis have enabled better predictions of the biological behavior of these tumors. We review their cytogenetic features and prognosis and also provide an update of the most recent recommendations for management.

Adolescent and Young Adult Cancer Biology

Adolescent and young adult (AYA) patients with cancer have not attained the same improvements in overall survival as either younger children or older adults. One possible reason for this disparity may be that the AYA cancers exhibit unique biologic characteristics, resulting in differences in clinical and treatment resistance behaviors. Our current understanding of the unique biological/genomic characteristics of AYA cancers is limited. However, there has been some progress that has provided clues about the biology of AYA cancers. We here review the latest findings in the area of AYA cancer biology and discuss what is required to advance the field for the more effective treatment of this patient population.

A Case of Adjacent, Clonally Distinct Borderline Melanocytic Tumors on the Arm

Atypical Spitz tumor (AST) is a melanocytic proliferation that shares histopathologic features of Spitz nevus and spitzoid melanoma. Distinction of AST from spitzoid melanoma is critical because the majority of ASTs will follow an indolent course. Array-based comparative genomic hybridization (aCGH) has been suggested as a potential tool for evaluating malignant potential in spitzoid tumors. We present a case of a 52-year-old woman with an AST in which aCGH was crucial in guiding correct diagnosis and management. The patient first presented with a flesh-colored papule on her arm that was changing color. Biopsy revealed a dermal nevoid melanocytic tumor of indeterminate histopathology, favored to be a severely atypical nevus. The tumor was excised. One year later, another flesh-colored papule proximal to the excision site of the first tumor was biopsied and showed a predominantly dermal atypical spitzoid melanocytic proliferation with a differential diagnosis of AST versus spitzoid melanoma. Recurrent or metastatic melanoma was also a concern given proximity to the previous excision site. Molecular analysis of both lesions by aCGH revealed distinct molecular signatures, supporting the 2 tumors to be clonally unrelated. Furthermore, the new tumor displayed limited evidence of genomic instability, supporting classification as an AST with predicted indolent behavior. This case highlights the utility of aCGH in evaluating borderline melanocytic lesions, including assessment of malignant potential in ASTs, and clonality analysis to assist in exclusion of metastatic disease.

Genomic Landscape of Spitzoid Neoplasms Impacting Patient Management

Spitzoid neoplasms are a distinct group of melanocytic proliferations characterized by epithelioid and/ or spindle shaped melanocytes. Intermediate forms that share features of both benign Spitz nevi (SN) and Spitz melanoma, i.e., malignant Spitz tumor (MST) represent a diagnostically and clinically challenging group of melanocytic lesions. A multitude of descriptive diagnostic terms exist for these ambiguous lesions with atypical Spitz tumor (AST) or Spitz tumor of uncertain malignant potential (STUMP) just naming two of them. This diagnostic gray zone creates confusion and high insecurity in clinicians and in patients. Biological behavior and clinical course of this intermediate group still remains largely unknown, often leading to difficulties with uncertainties in clinical management and prognosis. Consequently, a better stratification of Spitzoid neoplasms in benign and malignant forms is required thereby keeping the diagnostic group of AST/STUMP as small as possible. Ancillary diagnostic techniques such as immunohistochemistry, comparative genomic hybridization, fluorescence in situ hybridization, next generation sequencing, micro RNA and mRNA analysis as well as mass spectrometry imaging offer new opportunities for the distinct diagnosis, thereby allowing the best clinical management of Spitzoid neoplasms. This review gives an overview on these additional diagnostic techniques and the recent developments in the field of molecular genetic alterations in Spitzoid neoplasms. We also discuss how the recent findings might facilitate the diagnosis and stratification of atypical Spitzoid neoplasms and how these findings will impact the diagnostic work up as well as patient management. We suggest a stepwise implementation of ancillary diagnostic techniques thereby integrating immunohistochemistry and molecular pathology findings in the diagnosis of challenging ambiguous Spitzoid neoplasms. Finally, we will give an outlook on pending future research objectives in the field of Spitzoid melanocytic lesions.

Primary and Metastatic Melanoma With NTRK Fusions

A number of oncogenic driver mutations have been identified in melanocytic nevi and melanoma, but translocations also play a role in tumorigenesis and provide potential therapeutic targets for malignant lesions. Various translocations, such as those involving the anaplastic lymphoma kinase (ALK), neurotrophic tropomyosin receptor kinase 1 (NTRK1), and NTRK3 have been reported in spitzoid melanocytic neoplasms leading to kinase-fusion proteins that result in immunohistochemically detectable ALK or NTRK expression. We have previously reported that ALK expression can be found in nonspitzoid primary and metastatic cutaneous melanomas. In this study we report that nonspitzoid metastasizing melanomas of adults may also harbor NTRK fusions and that NTRK expression can be immunohistochemically detected in these tumors. Of 751 melanomas analyzed by next-generation sequencing, 4 metastatic melanomas were identified with NTRK fusions, 3 involving NTRK1, 1 involving NTRK2. They occurred in 3 women and 1 man. Two of the corresponding primary tumors were from the trunk, 1 from an extremity and 1 tumor arose in anal skin. One primary tumor displayed features of superficial spreading melanoma and 3 were nodular melanomas. All tumors were cytologically characterized by the presence of large epithelioid melanocytes. All tumors were immunoreactive with anti-Trk antibody. Next-generation sequencing documented that the NTRK1 fusion partners included TRIM63, DDR2, and GON4L. One tumor harbored an NTRK2-TRAF2 fusion. Thus, our findings document that NTRK kinase fusions can occur in nonspitzoid metastasizing melanomas of adults. The presence of an NTRK family fusion in these tumors may provide a therapeutic opportunity in a small subset of patients with metastatic melanoma.

A Practical Approach to the Diagnosis of Melanocytic Lesions

CONTEXT.—

Melanocytic lesions are common in routine surgical pathology. Although the majority of these lesions can be confidently diagnosed using well-established morphologic criteria, there is a significant subset of lesions that can be diagnostically difficult. These can be a source of anxiety for patients, clinicians, and pathologists, and the potential consequences of a missed diagnosis of melanoma are serious.

OBJECTIVE.—

To provide a practical approach to the diagnosis of melanocytic lesions, including classic problem areas as well as suggestions for common challenges and appropriate incorporation of ancillary molecular techniques.

DATA SOURCES.—

Literature search using PubMed and Google Scholar, incorporating numerous search terms relevant to the particular section, combined with contemporaneous texts and lessons from personal experience.

CONCLUSIONS.—

Although a subset of melanocytic lesions can be diagnostically challenging, the combination of a methodical approach to histologic assessment, knowledge of potential diagnostic pitfalls, opinions from trusted colleagues, and judicious use of ancillary techniques can help the pathologist navigate this difficult area.

An update on molecular alterations in melanocytic tumors with emphasis on Spitzoid lesions

Significant progress in the molecular pathology of melanocytic tumors have revealed that benign neoplasms, so-called nevi, are initiated by gain-of-function mutations in one of several primary oncogenes, such as BRAF in acquired melanocytic nevi, NRAS in congenital nevi or GNAQ/GNA11 in blue nevi, with consequent MAPK and PI3K/AKT/mTOR activation. Secondary genetic alterations overcome tumor suppressive mechanisms and allow the progression to intermediate lesions characterized by TERT-p mutation or to invasive melanomas displaying disruption of tumor suppressor genes. Currently, melanoma is molecularly regarded as four different diseases, namely BRAF, NRAS, NF1 and the "triple wild type" subtypes, which are associated with particular clinicopathological features. Melanocytic Spitzoid lesions include benign Spitz nevus, atypical Spitz tumor (AST) and Spitzoid melanoma. This is a challenging diagnostic group, particularly with regard to the distinction between AST and Spitzoid melanoma on clinical and histological grounds. Molecular analysis has identified the presence of HRAS mutation, BAP1 loss (often accompanying by BRAF mutations) or several kinase fusions in distinct categories of Spitz tumors. These aberrations account for the rapid growth characteristic of Spitz nevi. Subsequent growth is halted by various tumor suppressive mechanisms abrogation of which allow the development of AST, now better classified as low-grade melanocytic tumor. Although at present ancillary genetic techniques have not been very helpful in the prediction of biological behavior of AST, they have defined distinct tumor subsets differing with regard to biology and histology. Finally, we discuss how novel molecular markers may assist the differential diagnosis of melanoma, particularly from malignant peripheral nerve sheath tumor (MPNST). It is anticipated that the significant progress in the field of molecular pathology regarding the various types of melanocytic tumors, will eventually contribute to a more accurate histologic categorization, prediction of biologic behavior and personalized treatment.

Pathology and genomics of pediatric melanoma: A critical reexamination and new insights

The clinicopathologic features of pediatric melanoma are distinct from those of the adult counterpart. For example, most childhood melanomas exhibit a uniquely favorable biologic behavior, save for those arising in large/giant congenital nevi. Recent studies suggest that the characteristically favorable biologic behavior of childhood melanoma may be related to extreme telomere shortening and dysfunction in the cancer cells. Herein, we review the genomic profiles that have been defined for the different subtypes of pediatric melanoma and particularly emphasize the potential prognostic value of telomerase reverse transcriptase alterations for these tumors.

Spitz Tumors of the Skin

Spitz tumors are melanocytic neoplasms hallmarked by large cell size, lack of high-grade atypia, and a regular architecture. Most are nonpigmented or poorly pigmented. Malignant potential ranges from absent (Spitz nevus), to fully present (spitzoid melanoma), with a further, ill-defined group of Spitz tumors with limited metastatic potential. Microscopic evaluation may prove inconclusive in some instances, resulting in a verdict of Spitz tumor of uncertain malignant potential (STUMP). STUMP is, therefore, not an entity, and should not be equated with Spitz tumors with limited metastatic potential. Novel diagnostic techniques are yielding promising results, and further evaluation is ongoing.

Paediatric melanoma

Paediatric melanoma, although rare, is the most common skin cancer in children. Our current knowledge on paediatric melanoma incidence trends is expanding, as several studies have addressed this issue with conflicting results. Known risk factors for paediatric melanoma include family history of melanoma, a previous history of malignancy, large congenital nevi, numerous melanocytic nevi, sunburns, increased UV exposure and a sun-sensitive phenotype. In younger children, melanoma more often presents with atypical features, such as a changing, amelanotic or uniformly coloured, often bleeding lesion, not fulfilling in most cases the conventional ABCDE criteria. The major differential diagnoses are melanocytic nevi, proliferative nodules in congenital nevi and atypical Spitz tumours. Moreover, in the younger age group non-Caucasian children are over-represented, tumours tend to be thicker and lymph nodes are often involved. Despite the frequent diagnosis at an advanced stage, the overall survival is fair in paediatric melanoma. Specific guidelines for management of melanoma in children do not exist, and most often the disease is treated similarly to melanoma in adults.

Spitz Nevi and Other Spitzoid Neoplasms in Children: Overview of Incidence Data and Diagnostic Criteria

Spitz nevi are benign melanocytic neoplasms characterized by epithelioid or spindle melanocytes or both. In some rare cases their presentation overlaps with the clinical and histopathologic features of malignant melanoma, so a differential diagnosis can be difficult to make. Intermediate forms between Spitz nevi and malignant melanoma, with unpredictable behavior, have been called atypical Spitz tumors. A literature search was performed to review the clinical, dermoscopic, genetic, and histopathologic aspects of spitzoid tumors. Spitz nevi mainly occur in children, with no predilection for sex, and in young women. Common sites are the head and lower arms, where Spitz nevi present as pink nodules or hyperpigmented plaques. Spitzoid lesions may have diverse dermoscopic patterns: vascular, starburst, globular, atypical, reticular, negative homogeneous, or targetoid. The management of spitzoid lesions can be invasive or conservative; surgical excision is usually reserved for those with doubtful features, whereas clinical and dermoscopic follow-up is preferred for typical pediatric Spitz nevi. The role of sentinel lymph node biopsy in atypical Spitz tumors is debated. Immunohistochemistry and new molecular techniques such as comparative genomic hybridization, polymerase chain reaction, and fluorescence in situ hybridization offer new diagnostic perspectives, investigating genetic alterations that are specific for malignant melanoma or for Spitz nevi.

Genetics of melanocytic nevi

Melanocytic nevi are a benign clonal proliferation of cells expressing the melanocytic phenotype, with heterogeneous clinical and molecular characteristics. In this review, we discuss the genetics of nevi by salient nevi subtypes: congenital melanocytic nevi, acquired melanocytic nevi, blue nevi, and Spitz nevi. While the molecular etiology of nevi has been less thoroughly studied than melanoma, it is clear that nevi and melanoma share common driver mutations. Acquired melanocytic nevi harbor oncogenic mutations in BRAF, which is the predominant oncogene associated with melanoma. Congenital melanocytic nevi and blue nevi frequently harbor NRAS mutations and GNAQ mutations, respectively, while Spitz and atypical Spitz tumors often exhibit HRAS and kinase rearrangements. These initial 'driver' mutations are thought to trigger the establishment of benign nevi. After this initial phase of the cell proliferation, a senescence program is executed, causing termination of nevi growth. Only upon the emergence of additional tumorigenic alterations, which may provide an escape from oncogene-induced senescence, can malignant progression occur. Here, we review the current literature on the pathobiology and genetics of nevi in the hope that additional studies of nevi promise to inform our understanding of the transition from benign neoplasm to malignancy.

Melanoma: Kids are not just little people

Malignant melanoma can affect patients of any age. It has been well documented that the overall incidence of melanoma has increased in the past several decades, and this increase extends to the pediatric population (both preadolescent and, to a greater extent, adolescent children). Melanoma in adolescents, commonly defined as patients 11 to 19 years of age, behaves similarly to melanoma in adults; however, there are a number of distinct differences in the presentation and prognosis of melanoma in the preadolescent population. Though our treatment options for melanoma are increasing with the advent of novel drugs and clinical trials, the rarity of pediatric melanomas often excludes this population from clinical studies. The treatment options for the pediatric patient are predominantly based on adult clinical trials. Awareness of the differences in clinical presentation, as well as management of melanoma in younger patients compared with their adult counterparts, is crucial to guarantee prompt and appropriate care.

A diagnostic algorithm for atypical spitzoid tumors: guidelines for immunohistochemical and molecular assessment

Atypical spitzoid tumors are a morphologically diverse group of rare melanocytic lesions most frequently seen in children and young adults. As atypical spitzoid tumors bear striking resemblance to Spitz nevus and spitzoid melanomas clinically and histopathologically, it is crucial to determine its malignant potential and predict its clinical behavior. To date, many researchers have attempted to differentiate atypical spitzoid tumors from unequivocal melanomas based on morphological, immonohistochemical, and molecular diagnostic differences. A diagnostic algorithm is proposed here to assess the malignant potential of atypical spitzoid tumors by using a combination of immunohistochemical and cytogenetic/molecular tests. Together with classical morphological evaluation, this algorithm includes a set of immunohistochemistry assays (p16(Ink4a), a dual-color Ki67/MART-1, and HMB45), fluorescence in situ hybridization (FISH) with five probes (6p25, 8q24, 11q13, CEN9, and 9p21), and an array-based comparative genomic hybridization. This review discusses details of the algorithm, the rationale of each test used in the algorithm, and utility of this algorithm in routine dermatopathology practice. This algorithmic approach will provide a comprehensive diagnostic tool that complements conventional histological criteria and will significantly contribute to improve the diagnosis and prediction of the clinical behavior of atypical spitzoid tumors.

Primary and Metastatic Cutaneous Melanomas Express ALK Through Alternative Transcriptional Initiation

A number of common driver mutations have been identified in melanoma, but other genetic or epigenetic aberrations are also likely to play a role in the pathogenesis of melanoma and present potential therapeutic targets. Translocations of the anaplastic lymphoma kinase (ALK), for example, have been reported in spitzoid melanocytic neoplasms leading to kinase-fusion proteins that result in immunohistochemically detectable ALK expression. In this study, we sought to determine whether ALK was also expressed in nonspitzoid primary and metastatic cutaneous melanomas. ALK immunohistochemistry was performed on 603 melanomas (303 primary and 300 metastatic tumors) from 600 patients. ALK immunohistochemistry expression was identified in 7 primary and 9 metastatic tumors. In 5 of 7 primary tumors and in 6 of 9 metastatic lesions, the majority of tumor cells were immunoreactive for ALK. In the other 2 primary and 3 metastatic lesions, positive staining was identified in less than half of the tumor cells. ALK positivity was found in the presence or absence of BRAF or NRAS mutations. In contrast to prior observations with ALK-positive Spitz tumors, none of the ALK-positive melanomas harbored a translocation. Instead, the ALK-positive melanomas predominantly expressed the recently described ALK isoform, ALK, which lacks the extracellular and transmembrane domains of wild-type ALK, consists primarily of the intracellular tyrosine kinase domain, and originates from an alternative transcriptional initiation site within the ALK gene. The findings are clinically relevant as patients with metastatic melanoma who have ALK expression may potentially benefit from treatment with ALK kinase inhibitors.

Selected benign cutaneous lesions that may simulate melanoma histologically

As cutaneous melanomas manifest a wide spectrum of clinical and pathologic presentations, several other lesions enter into their differential diagnosis. This article considers those entities, including melanocytic hyperplasia, cellular nodules in congenital nevi, atypical lentiginous melanocytic proliferations, "special site" nevi, epithelioid histiocytoma, neurothekeoma, cellular schwannoma, and proliferating scars.