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.

[Gene expression profiling in melanoma diagnostics: problems and future application in clinical practice]

Difficulties in the diagnosis and differential diagnosis of melanoma in the work of a pathologist include not only conflicting structural and morphological features, but also the insufficient effectiveness of biochemical and some molecular markers in immunohistochemical studies. The review presents modern alternative methods for diagnosing malignant tumors based on the assessment of gene expression, the performance, objectivity and reliability of the determination of which may in the future have clinical application as an addition to histopathological methods in the diagnosis and differential diagnosis of various malignant neoplasms, including melanocytic neoplasms, which is changing the paradigm of routine medical practice, introducing diagnostic tests that carry molecular information into it.

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.

Invasive melanoma in a 5-year-old Canadian patient: A case report

Atypical Spitzoid lesions pose a distinct challenge in classification as they may comprise a mixture of both classic benign nevus and cutaneous melanoma characteristics. Immunostaining and molecular analysis, such as comparative genomic hybridization, can assist in narrowing the differential diagnosis. We present a case of a 5-year-old male with an atypical Spitzoid lesion on his back. Initial histopathology revealed a relatively symmetric lesion with mitotic figures and poor maturation of melanocytes with descent into the dermis. Immunohistochemistry demonstrated a loss of p16, and array comparative genomic hybridization revealed a loss of chromosome 9, supporting a diagnosis of invasive melanoma arising in conjunction with a remnant of a conventional melanocytic nevus. This case is the first in Canada to demonstrate the use of array comparative genomic hybridization for diagnosing melanoma in a young paediatric patient.

Molecular testing practices and perceptions among dermatopathologists

BACKGROUND

We evaluated how dermatopathologists are employing molecular testing in the setting of neoplastic skin diseases, and assessed their opinions of the broader role and utility of molecular technologies in clinical practice.

METHODS

A 15-question online survey was sent to Fellows of the American Society of Dermatopathology in April 2017.

RESULTS

One hundred and thirty-six dermatopathologists completed the survey (response rate = 16%). A majority (94%) of respondents reported experience with one or more molecular testing strategies. Sixty-two percent of dermatopathologists order 12 or more molecular tests per year, while 5% of respondents order 2 or fewer assays per year. More frequent utilization of molecular testing is associated with relevant instruction during residency training (P = .009), primary board certification in pathology (P = .008), academic medical center affiliation (P = <.0001), higher volume clinical practice (P = .0004), presence of on-site clinical molecular pathology/cytogenetics laboratory (P = .007), and greater physician confidence incorporating test results into histopathological assessments (P = <.0001).

CONCLUSIONS

Wider adoption of molecular testing in dermatopathology may be limited by factors such as physician training, test costs/insurance coverage, logistical issues and lack of evidence-based clinical practice guidelines. Dermatopathologists have concerns regarding clinical validity/utility and inappropriate/overuse of some molecular tests. The importance of longitudinal education in molecular technologies and their applications for trainee and practicing physicians is highlighted.

An independent validation of a gene expression signature to differentiate malignant melanoma from benign melanocytic nevi

BACKGROUND

Recently, a 23-gene signature was developed to produce a melanoma diagnostic score capable of differentiating malignant and benign melanocytic lesions. The primary objective of this study was to independently assess the ability of the gene signature to differentiate melanoma from benign nevi in clinically relevant lesions.

METHODS

A set of 1400 melanocytic lesions was selected from samples prospectively submitted for gene expression testing at a clinical laboratory. Each sample was tested and subjected to an independent histopathologic evaluation by 3 experienced dermatopathologists. A primary diagnosis (benign or malignant) was assigned to each sample, and diagnostic concordance among the 3 dermatopathologists was required for inclusion in analyses. The sensitivity and specificity of the score in differentiating benign and malignant melanocytic lesions were calculated to assess the association between the score and the pathologic diagnosis.

RESULTS

The gene expression signature differentiated benign nevi from malignant melanoma with a sensitivity of 91.5% and a specificity of 92.5%.

CONCLUSIONS

These results reflect the performance of the gene signature in a diverse array of samples encountered in routine clinical practice. Cancer 2017;123:617-628. © 2016 American Cancer Society.

The influence of a gene expression signature on the diagnosis and recommended treatment of melanocytic tumors by dermatopathologists

It is well documented that histopathologic examination is sometimes inadequate for accurate and reproducible diagnosis of certain melanocytic neoplasms. Recently, a 23-gene expression signature has been clinically validated as an adjunctive diagnostic test to differentiate benign nevi from malignant melanomas. This study aimed to quantify the impact of this test on diagnosis and treatment recommendations made by dermatopathologists.Diagnostically challenging melanocytic lesions encountered during routine dermatopathology practice were submitted for gene expression testing and received a melanoma diagnostic score (MDS). Submitting dermatopathologists completed a survey documenting pre-test diagnosis, level of diagnostic confidence, and recommendations for treatment. The survey was repeated after receiving the MDS. Changes between the pre- and post-test surveys were analyzed retrospectively.When the MDS was available as part of a comprehensive case evaluation in diagnostically challenging cases, definitive diagnoses were increased by 56.6% for cases that were initially indeterminate and changes in treatment recommendations occurred in 49.1% of cases. Treatment recommendations were changed to align with the test result in 76.6% of diagnostically challenging cases.The MDS impacts diagnosis and treatment recommendations by dermatopathologists confronted with diagnostically challenging melanocytic lesions. Increased data are needed in order to completely understand how use of the MDS will translate from dermatopathology to clinical practice.

Metastatic melanoma in association with a giant congenital melanocytic nevus in an adult: controversial CGH findings

Giant congenital melanocytic nevi (GCMNs) represent a distress to patients for 2 reasons: one is disfigurement, and the other is the increased risk of developing secondary melanocytic tumors, such as benign proliferative nodules (BPNs) and malignant melanoma (MM). BPN present as a rapid growth nodule arising within a congenital melanocytic nevus (CMN) that often ulcerates, occurs in children younger than 2 years of age. BPNs arising within a CMN are exceedingly rare after childhood, and very few cases have been described in adults. Despite the worrisome clinical and histologic findings of BPN, most laboratory investigations seem to support their benignity. The distinction between MM and BPN is extremely important, but the histopathology of BPN of GCMN can be a challenge to differentiate from MM. In the recent years, molecular tests that investigate DNA copy number alterations such as fluorescence in situ hybridization and comparative genomic hybridization have shown promise to help guide the diagnosis of ambiguous melanocytic proliferations arising within CMNs. We report the case of a 22-year-old woman with a nodule arising in a GCMN and with an axillary mass suggesting a nodal metastasis of melanoma, and discuss the unusual clinical, histopathologic, and molecular findings that make this case particularly interesting.

Paediatric melanoma

Cutaneous melanoma occurs only rarely in children under 10 years of age. Mimics of melanoma, including Spitz naevi and proliferative nodules in congenital melanocytic naevi are much more frequent in this age group. Melanoma arising in congenital melanocytic naevus is uncommon, but can show aggressive behaviour. Although spitzoid lesions constitute the majority of 'diagnostically challenging' cases, they are an uncommon cause of mortality in this age group. Among lesions with undoubted metastatic potential, there are biologically distinct tumours which differ significantly in behaviour from the common types of melanoma seen in adults. In patients over 10 years of age and increasingly into the late adolescent years, melanoma is a relatively common neoplasm. Just as in adult patients, care should be taken to exclude melanoma mimics. Particular care is warranted in this older age group in the assessment of lesions with spitzoid morphology as there is significant potential for both over-and under-diagnosis.

Protein mislocalization: mechanisms, functions and clinical applications in cancer

The changes from normal cells to cancer cells are primarily regulated by genome instability, which foster hallmark functions of cancer through multiple mechanisms including protein mislocalization. Mislocalization of these proteins, including oncoproteins, tumor suppressors, and other cancer-related proteins, can interfere with normal cellular function and cooperatively drive tumor development and metastasis. This review describes the cancer-related effects of protein subcellular mislocalization, the related mislocalization mechanisms, and the potential application of this knowledge to cancer diagnosis, prognosis, and therapy.

Spitz nevus, Spitz tumor, and spitzoid melanoma: a comprehensive clinicopathologic overview

Spitz nevus can clinically present either in the classical (reddish pink) or the pigmented (brownish black) variant. Dermoscopy demonstrates that the pigmented variant is much more common than the classical variant; however, none of these show dermoscopic patterns clearly distinguishable from melanoma. Even histopathologically, a clear-cut differentiation between benign and malignant spitzoid neoplasms is often difficult, so that intermediate diagnostic categories (atypical Spitz nevus and Spitz tumor) are admitted. Because of these difficulties in clinical and histopathologic evaluation, surgical excision is recommended for clinically atypical spitzoid lesions of childhood and for all spitzoid lesions of adulthood.