Two cases of unusual acral melanocytic tumors: illustration of molecular cytogenetics as a diagnostic tool

Subungual melanoma: molecular analysis of 31 cases from early stage to invasive melanoma

AIMS

The distinction between the benign subungual melanocytic lesions and an early lesion of subungual melanoma (SUM) remains a diagnostic challenge. We evaluated the routine diagnostic utility of array Comparative Genomic Hybridization (aCGH) to detect whole-genome copy number variations (CNV) as well as targeted next-generation sequencing (NGS) in SUM.

METHODS AND RESULTS

This retrospective study included 20 cases of in situ SUM and 11 cases of invasive SUM. Analysis by aCGH detected common oncogene amplifications in all but one case of invasive SUM (n = 10) and in all cases of in situ SUM with a melanocyte count (MC) >45/mm (n = 4 true positive) and the average number of CNV was 8.5. Thirteen remaining cases of in situ SUM gave false negative results (n = 13), owing to a lack of sufficient melanocytes to analyse (median MC of 35.35; range: 10.16-39.5). Molecular analysis failed in four cases (three in situ SUM and one invasive SUM) due to insufficient amounts of DNA. Across the whole cohort, the sensitivity of aCGH was 52%, but when adjusting the cutoff to MC >45/mm, the sensitivity was 93%. Targeted NGS was less informative than aCGH analyses in our series of SUM.

CONCLUSION

To distinguish malignant from benign lesions, especially in situ SUM versus atypical lentiginous melanocytic proliferations, aCGH analysis should be performed when the MC is above 45 melanocytes per linear millimetre. This pangenomic method can detect oncogene amplifications, as well as a number of CNV >3, which strongly support the diagnosis of malignancy.

Melanoma in children: A systematic review and individual patient meta-analysis

The current evidence on paediatric melanoma is heterogeneous, especially regarding the prognosis of different histological subtypes. We sought to systematically review the evidence on paediatric melanoma, highlighting the major sources of heterogeneity and focusing on available data on single patients. A systematic search was performed from 1948 to 25 January 2021. Only studies reporting at least one case of cutaneous melanoma in patients aged ≤18 years were included. Unknown primary and uncertain malignant melanomas were excluded. Three couples of authors independently performed title/abstract screening and two different authors reviewed all the relevant full texts. The selected articles were manually cross-checked for overlapping data for qualitative synthesis. Subsequently data on single patients were extracted to perform a patient-level meta-analysis. PROSPERO registration number: CRD42021233248. The main outcomes were melanoma-specific survival (MSS) and progression-free survival (PFS) outcomes. Separate analyses were done of cases with complete information on histologic subtype, focusing on superficial spreading (SSM), nodular (NM) and spitzoid melanomas, as well as of those classified as de-novo (DNM) and acquired or congenital nevus-associated melanomas (NAM). The qualitative synthesis covered 266 studies; however, data on single patients were available from 213 studies including 1002 patients. Among histologic subtypes, NM had a lower MSS than both SSM and spitzoid melanoma, and a lower PFS than SSM. Spitzoid melanoma had a significantly higher progression risk than SSM and trended toward lower mortality. Focusing on nevus-associated status, DNM demonstrated better MSS after progression than congenital NAM, and no differences were highlighted in PFS. Our findings describe the existence of different biological patterns in paediatric melanoma. Specifically, spitzoid melanomas demonstrated intermediate behaviour between SSM and NM and showed a high risk of nodal progression but low mortality. This raises the question of whether spitzoid lesions are being over-diagnosed as melanoma in childhood.

Subungual Melanocytic Lesions in Pediatric Patients

The study of subungual melanocytic lesions can present challenges because of the clinical and histologic characteristics of the nail unit and the difficulty of performing nail biopsies and processing specimens. These lesions can be even more challenging in children due to differences in clinical and epidemiological profiles between the adult and pediatric populations. Many of the clinical features of subungual melanocytic lesions that would raise alarm in an adult do not have the same implications in children. Consensus is also lacking on when a nail biopsy is needed to rule out malignancy in the pediatric setting. In view of these considerations and the rarity of subungual melanoma in childhood, the recommended approach in most cases is a watch-and-wait strategy. Subungual melanocytic lesions in children may also show atypical histopathologic features that are not necessarily associated with aggressive behavior. Subungual melanoma is very rare in childhood, with just 21 cases described to date. None of the patients developed visceral metastasis or died as a result and the diagnosis was controversial in many of the cases. Considering the above and the significantly higher frequency and particular characteristics of longitudinal melanonychia with a benign etiology in children, subungual melanocytic lesions should be managed differently in this setting than in adults. In most cases, a watch-and-wait approach is the most appropriate strategy.

An Evidence-Based Approach to Pediatric Melanonychia

Melanonychia including melanonychia striata in children poses a diagnostic dilemma. Atypical clinical features often raise the possibility of malignancy, and a nail unit biopsy may be recommended. Commensurate with atypical clinical features, the histopathology may also appear alarming. However, accumulating data illustrate that most cases of melanonychia striata are benign and suggest that an alternate approach is often warranted for pediatric patients. Herein, we review the existing data regarding pediatric melanonychia striata and offer an evidence-based approach to its evaluation and management.

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.

Melanocytic nevi simulant of melanoma with medicolegal relevance

A group of melanocytic benign nevi are prone to be misdiagnosed as nodular or superficial spreading melanoma. This review illustrates the most frequent forms of these nevi in direct comparison with their malignant morphologic counterparts. The nevi are: hyper-cellular form of common nevus to be distinguished from nevoid melanoma, Spitz nevus (vs spitzoid melanoma), Reed nevus (vs melanoma with features of Reed nevus), cellular atypical blue nevus (vs melanoma on blue nevus), acral nevus (vs acral melanoma), Clark dysplastic nevus (vs superficial spreading melanoma), desmoplastic nevi (vs desmoplastic melanoma), benign proliferative nodules in congenital nevi (vs melanoma on congenital nevi), epithelioid blue nevus (vs animal type melanoma) and regressed nevus (vs regressed melanoma). For each single 'pair' of morphological look-alikes, a specific set of morphological, immunohistochemical and genetic criteria is provided.

Pigmented nail disorders

Nail pigmentation is defined by the presence of melanin in the nail plate. It most frequently has the appearance of a longitudinal pigmented band, called longitudinal mel-anonychia (LM). LM is an important aspect of ungual pathology because it can be the first sign of nail apparatus melanoma. The aim of this article is to help distinguish those types of melanonychia that are worrisome and should lead to biopsy from those that are reasonably reassuring and need only be followed clinically. Histology, differential diagnosis, and biopsy techniques also are considered.

Genetic alterations in melanocytic tumors

In the last decade, significant progress has been made in our understanding of the genetic alterations in melanocytic tumors. The most exciting finding is the discovery of oncogenic BRAF mutations in both malignant melanoma and melanocytic nevi. This finding indicates that activation of the mitogen-activated protein kinase pathway may be a critical initiating step of melanocytic neoplasia, and that the fundamental difference between melanoma and nevi may lie in the inhibitory machinery for this oncogenic signaling. In addition, different genetic alterations identified in melanomas at different sites and with different levels of sun exposure have been shown, indicating that there are several distinct genetic pathways in the development of melanoma. Different patterns of genetic alterations have also been identified among different kinds of melanocytic nevi. While acquired nevi and small congenital nevi show a high frequency of BRAF mutations regardless of their anatomic localization, the mutations were rare in medium-sized congenital nevi and giant congenital nevi. Spitz nevi show no BRAF mutations, while a subset of cases show HRAS mutations, often associated with a copy number increase of chromosome 11p. The clear differences in genetic aberration patterns have significant clinical implications in the diagnosis and treatment of melanocytic tumors.

Genome profiling of melanocytic tumors using multiplex ligation-dependent probe amplification (MLPA): Its usefulness as an adjunctive diagnostic tool for melanocytic tumors

BACKGROUND

The histopathology of melanocytic tumors sometimes presents diagnostic problems. Applicable parameters other than routine pathology are needed.

OBJECTIVE

We assessed the feasibility of multiplex ligation-dependent probe amplification (MLPA), a novel PCR-based genome profiling method, in the classification of melanocytic tumors.

METHOD

We extracted DNA from paraffin-embedded tissue sections of 24 primary melanomas, 14 Spitz nevi and 17 common melanocytic nevi. We analyzed the copy number gains or losses of a total of 76 genes spanning almost all chromosome arms using commercially available MLPA kits.

RESULTS

Although four melanocytic nevi and three Spitz nevi did not yield sufficient DNA for reliable analysis due to small tumor size, the MLPA analysis was feasible and applicable to the remaining 88% of samples. We found multiple genetic aberrations in primary melanomas. The total number of aberrations in each tumor ranged from 1 to 32 (average, 12.04). All but two melanomas showed aberrations at more than three genetic loci. Seventeen (70.8%) of the 24 melanomas showed a copy number loss of either the CDKN2A or CDKN2B gene on chromosome 9p21. All the Spitz nevi and 7 (50%) of 14 common melanocytic nevi had copy number changes at one or two gene loci (average, 1.04). The receiver operator characteristic curve analysis showed that the threshold value of copy number aberrations corresponding to 98% specificity for melanoma was 2.42 and the sensitivity using this threshold value was 92.5%.

CONCLUSIONS

MLPA could be used as an adjunctive diagnostic tool for melanocytic tumors.

Expression profiling reveals novel pathways in the transformation of melanocytes to melanomas

Affymetrix and spotted oligonucleotide microarrays were used to assess global differential gene expression comparing normal human melanocytes with six independent melanoma cell strains from advanced lesions. The data, validated at the protein level for selected genes, confirmed the overexpression in melanoma cells relative to normal melanocytes of several genes in the growth factor/receptor family that confer growth advantage and metastasis. In addition, novel pathways and patterns of associated expression in melanoma cells not reported before emerged, including the following: (a) activation of the NOTCH pathway; (b) increased Twist expression and altered expression of additional transcriptional regulators implicated in embryonic development and epidermal/mesenchymal transition; (c) coordinated activation of cancer/testis antigens; (d) coordinated down-regulation of several immune modulation genes, in particular in the IFN pathways; (e) down-regulation of several genes implicated in membrane trafficking events; and (f) down-regulation of growth suppressors, such as the Prader-Willi gene NECDIN, whose function was confirmed by overexpression of ectopic Flag-necdin. Validation of differential expression using melanoma tissue microarrays showed that reduced ubiquitin COOH-terminal esterase L1 in primary melanoma is associated with worse outcome and that increased expression of the basic helix-loop-helix protein Twist is associated with worse outcome. Some differentially expressed genes reside on chromosomal regions displaying common loss or gain in melanomas or are known to be regulated by CpG promoter methylation. These results provide a comprehensive view of changes in advanced melanoma relative to normal melanocytes and reveal new targets that can be used in assessing prognosis, staging, and therapy of melanoma patients.