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.

Update on nail unit histopathology

Histopathologic evaluation of the nail unit is an essential component in the diagnosis of nail unit disorders. This review highlights recent updates in nail unit histopathology and discusses literature covering a wide range of nail disorders including melanoma/melanocytic lesions, squamous cell carcinoma, onychomatricoma, onychopapilloma, onychomycosis, lichen planus, and other inflammatory conditions. Herein we also discuss recent literature on nail clipping histopathology, a useful and noninvasive diagnostic tool that continues to grow in popularity and importance to both dermatologists and dermatopathologists.

Gastric metastasis from nodular malignant melanoma of the auricle with multigene aberrations: A rare case report and literature review

Primary malignant melanoma (MM) of the external ear accounts for a low proportion of cases of cutaneous MM, and its incidence in non-white women is very low. The stomach is a rare metastatic site for MM. Gastric metastasis of MM of the external ear is extremely rare, and the associated gene alterations and mechanisms are poorly understood. The present report describes the case of a 58-year-old Asian woman who had a mass on the left auricle for 5 years and was diagnosed with nodular MM with the BRAF V600E mutation after surgical resection. Postoperative metastases to the stomach and descending duodenum appeared 1 year after resection. After 11 months of BRAF-targeted therapy and immunotherapy, the patient developed drug resistance and died from systemic metastases to the brain, lungs, liver, left adrenal gland and peritoneum. Genetic testing revealed additional aberrations in MYB, p16, MYC and PTEN. The clinical characteristics of MM of the external ear and gastric metastatic MM were also summarized through a retrospective literature review. Immunohistochemical staining is critical in the diagnosis of gastric metastasis from MM of the external ear. This disease often requires a multidisciplinary treatment approach, including surgery, targeted therapy and immunotherapy. The present study provides some genetic information about this rare disease and discusses appropriate treatment strategies. The findings of the present study suggests that the surgical margin size, tumor histological type and number of genetic aberrations may be closely associated with metastasis potential, therapeutic efficacy and patient outcome.

Nail Apparatus Melanoma: Current Management and Future Perspectives

Nail apparatus melanoma (NAM) is a rare type of cutaneous melanoma that belongs to the acral melanoma subtype. NAM is managed principally in accordance with the general treatment for cutaneous melanoma, but there is scarce evidence in support of this in the literature. Acral melanoma is genetically different from non-acral cutaneous melanoma, while recently accumulated data suggest that NAM also has a different genetic background from acral melanoma. In this review, we focus on recent advances in the management of NAM. Localized NAM should be surgically removed; amputation of the digit and digit-preserving surgery have been reported. Sentinel lymph node biopsy can be considered for invasive NAM for the purpose of accurate staging. However, it is yet to be clarified whether patients with metastatic sentinel lymph nodes can be safely spared completion lymph node dissection. Similar to cutaneous melanoma, immune checkpoint inhibitors and BRAF/MEK inhibitors are used as the first-line treatment for metastatic NAM, but data on the efficacy of these therapies remain scarce. The therapeutic effects of immune checkpoint inhibitors could be lower for NAM than for cutaneous melanoma. This review highlights the urgent need to accumulate data to better define the optimal management of this rare melanoma.

Hyperplastic melanocytes with chromosomal aberrations in surrounding skin of subungual melanoma: fluorescence in situ hybridization analysis using whole-slide digital imaging

AIMS

Subungual melanoma (SUM) is increasingly being treated with conservative surgery. Consequently, the evaluation of resection margins has increased in importance. However, in several cases it is difficult to distinguish the in-situ lesion of SUM from hyperplastic melanocytes in surrounding skin. We examined whether PReferentially expressed Antigen in MElanoma (PRAME) immunohistochemistry and fluorescence in situ hybridization (FISH) labeling of CCND1 (11q13), RREB1 (6p25), MYB (6q23), and centromere 6 (CEP6) genes differentiated SUM from hyperplastic melanocytes.

METHODS AND RESULTS

We reviewed specimens of 36 SUM cases and compared PRAME immunostains of invasive melanoma, melanoma in situ, and hyperplastic melanocytes. PRAME-positive cases accounted for 90.5% of invasive melanoma, 88.9% of in situ melanoma, and 59.4% of hyperplastic melanocyte specimens. While invasive and in situ melanomas in more than half of examined cases were diffusely positive, this was found for only 9.4% of hyperplastic melanocyte cases. Four-colored FISH using whole-slide digital imaging was used to analyze positive detection rates and changes in chromosomal aberrations. The FISH positive detection rate was 100% in invasive melanomas, 94.7% in melanomas in situ, and 66.7% in hyperplastic melanocytes. The number of RREB1 (6p25) signals per cell was significantly amplified following tumor progression.

CONCLUSION

Hyperplastic melanocytes in the surrounding skin of SUM, considered morphologically non-neoplastic, showed chromosomal aberrations similar to those in melanoma. Such cells are also thought similar to the field cells of acral melanomas. Thus, whole-slide digital imaging is a technique that allows the evaluation of individual melanocyte lesions by FISH.

Subungual melanoma with blue naevus-like morphological features: a clinicopathological retrospective analysis of nine cases

Melanocytic lesions in the nail apparatus are often challenging. Both subungual melanomas (SUM) and blue naevus of the nail are very rare. Occasionally, melanomas may mimic blue naevus histologically. Benign and malignant blue melanocytic lesions are commonly associated with G protein mutations, a distinct abnormality not associated with conventional subungual melanomas. We describe the clinical, histological and immunohistochemical features of nine cases of SUM with blue naevus-like morphological features. Mutations in exon 4 and 5 of GNAQ and GNA11 were investigated in two cases, which showed no mutations. RNA-seq of one case revealed unknown mutations along with mutations in ATM, METK and ARID1A. Our study delineates a variant of SUM that mimics blue naevus. Awareness of this pitfall is important when evaluating heavily pigmented lesions around the nail in order to avoid misdiagnosis. Appropriate sampling of subungual lesions and clinicopathological correlation are paramount to reach the correct diagnosis.

Immunohistochemistry for Preferentially Expressed Antigen in Melanoma in the Differential Diagnosis of Melanocytic Lesions of the Nail Apparatus

ABSTRACT

Nail unit melanocytic lesions present a unique set of diagnostic challenges because of the unfamiliarity with clinical assessment and the lack of experience with histologic examination. Because the first surgical specimen received in the pathology laboratory is typically small, sometimes suboptimal biopsy, the distinction between melanoma and its histologic mimics can be difficult. For this reason, there has been a continued interest in the development of ancillary markers that may assist in the differential diagnosis of nail unit melanocytic lesions. Upregulation of preferentially expressed antigen in melanoma (PRAME) has been reported to be a common event in melanomas, and PRAME immunohistochemistry has been shown to be helpful in evaluating various melanocytic neoplasms. In this study, we evaluated PRAME protein expression in a series of nail unit melanocytic lesions. Twenty-five nail unit melanomas (including small biopsy and amputation specimens) and 32 control benign melanocytic lesions were retrospectively retrieved. Nuclear PRAME staining was scored as percentage and intensity labeling. All melanoma cases showed the nuclear expression of PRAME, which was usually diffuse and strong. In specimens where the neoplastic cells are limited in number, the staining was restricted to the tumor cells, corresponding to the initial H&E impression. All control cases were negative for PRAME expression. PRAME expression is helpful in distinguishing between melanomas and other nail unit melanocytic lesions. This antibody also proved to be diagnostically valuable in detecting melanoma cells in small specimens with minimal disease.

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.

Pathology of the Nail Unit

This article discusses the histologic findings in key nail unit diseases, including inflammatory, infectious, and neoplastic conditions. The emphasis is on clinicopathologic correlates, best practices to demonstrate the relevant histopathologic features, and pitfalls in diagnosis. Understanding the pathology of these disorders enhances clinical acumen and may affect the choice of biopsy procedures and treatment measures, with the outcome of better clinical care for patients with nail disease.

Clinicopathological, immunohistochemical and fluorescence in-situ hybridisation features of early subungual melanoma: an analysis of 65 cases

AIMS

Very limited data are available concerning the clinicopathological and molecular features of early subungual melanoma (SM), especially with regard to the Asian population. The aim of this study was to investigate the clinical, histological, immunohistochemical and chromosomal features of early SM.

METHODS AND RESULTS

Fifty-two in-situ and 13 thin (Breslow thickness ≤1.0 mm) SM cases were retrospectively reviewed. All patients presented with longitudinal melanonychia involving a single digit, and the thumb was the most affected digit (35 of 65, 53.8%). Microscopically, most cases showed small to medium nuclear enlargement (58 of 65) and mild to moderate nuclear atypia (57 of 65). Hyperchromatism and irregular contours of nuclei were persistent features in all cases. The variation of melanocyte count (the number of melanocytes per mm dermal-epithelial junction) ranged from 31 to 255. Intra-epithelial mitoses were identified in 34 cases (52.3%). Statistically, features of in-situ lesions including higher melanocyte count (>70), presence of multinucleated melanocytes, inflammatory infiltrate and cutaneous adnexal extension, were associated with early invasion. Melan-A, human melanoma B (HMB)45, mouse monoclonal melanoma antibody (PNL2) and SOX10 antibodies (>95.0%) showed superior diagnostic sensitivity to S-100 protein (83.1%). Fluorescence in-situ hybridisation (FISH) results were positive in 15 of 23 successfully analysed cases.

CONCLUSIONS

To the best of our knowledge, this is the largest single-institution study of early SM in an Asian population, and the largest cohort tested by FISH. Early SM mainly showed small to medium nuclear enlargement and mild to moderate nuclear atypia. High melanocyte count, hyperchromatism and irregular contours of nuclei and intra-epithelial mitoses are crucial diagnostic parameters. Immunohistochemistry, especially SOX10 staining, and FISH analysis are valuable in the diagnosis of SM.

Mutation profile of primary subungual melanomas in Caucasians

Background: Specific genomic profile of cutaneous melanomas is related to UVR exposure, which exerts biological and therapeutic impact. Subungual melanoma (SUM) is an exceedingly rare disease; therefore, it is not well characterized. SUM pathogenesis is not related to UVR induced DNA damage and expected to differ from other melanoma subtypes. Our study aimed to define the mutation profile of SUM in Caucasians.

Materials and Methods: Next-generation sequencing-based genomic analysis was used to identify frequently mutated loci in 50 cancer-related genes in 31 SUM primary tumors.

Results: The most abundant mutations in SUM were found in KIT – in 13% of cases and NRAS – also in 13%, while BRAF - only in 3% of cases.

Conclusions: Our findings confirmed a high frequency of KIT and NRAS mutations in SUM, as well as a low incidence of BRAF mutations. We reported novel KRAS, CTNNB1, TP53, ERBB2, and SMAD4 mutations in SUM. Our findings provide new insights into the molecular pathogenesis of SUM.

Loss of BAP1 Expression in Atypical Mesothelial Proliferations Helps to Predict Malignant Mesothelioma

Distinguishing reactive mesothelial proliferation from malignant mesothelioma (MM) can be difficult, particularly on small biopsies. In this scenario, a diagnosis of atypical mesothelial proliferation might be rendered. However, the distinction between a reactive process and MM is important for prognosis and treatment. Recently, loss of BRCA1-associated protein 1 (BAP1) expression and/or homozygous deletion of CDKN2A were identified in some MM, but not in reactive mesothelial proliferations. We studied 34 cases of atypical mesothelial proliferation from our institutional files (1993 to 2016) for BAP1 expression, deletion of CDKN2A, and clinical outcome. Fifteen of 34 patients (44%) were subsequently diagnosed with MM. BAP1 expression was lost in 6 of these 15 (40%) patients. Ten of 15 (67%) patients died of disease within a median time of 18.2 months. BAP1 expression was also lost in 1 case of probable MM. In this case atypical mesothelial proliferation was identified in the pleura during a lobectomy procedure for lung adenocarcinoma. Follow-up of 57.0 months was remarkable for visceral and parietal pleural thickening with continued unilateral effusion identified on imaging studies but no subsequent definitive diagnosis of MM. CDKN2A studies by fluorescence in situ hybridization (performed in 31 cases) found no homozygous deletion of that gene in any case. In conclusion, loss of BAP1 expression in atypical mesothelial proliferation helps to predict MM and is a useful adjunct test in these cases. Homozygous deletion of CDKN2A in mesothelial cell proliferations did not prove to be useful to predict MM in cases of atypical mesothelial proliferation.

Development and validation of a novel clinical fluorescence in situ hybridization assay to detect JAK2 and PD-L1 amplification: a fluorescence in situ hybridization assay for JAK2 and PD-L1 amplification

The amplification of chromosome 9p24.1 encoding PD-L1, PD-L2, and JAK2 has been reported in multiple types of cancer and is associated with poor outcome, upregulation of PD-L1, and activation of the JAK/STAT pathway. We have developed a novel fluorescence in situ hybridization assay which combines 3 probes mapping to 9p24.1 with a commercial chromosome 9 centromere (CEN9) probe for detection of the JAK2/9p24.1 amplification. JAK2 fluorescence in situ hybridization was compared with array-based comparative genomic hybridization in 34 samples of triple negative breast cancer tumor. By array-based comparative genomic hybridization, 15 had 9p24.1 copy-number gain (log₂ratio>0.3) and 19 were classified as non-gain (log₂ratio≤0.3). Copy-number gain was defined as JAK2/CEN9 ratio ≥1.1 or average JAK2 signals≥3.0. Twelve of 15 samples with copy-number gain by array-based comparative genomic hybridization were also detected by fluorescence in situ hybridization. Eighteen of 19 samples classified as copy-number non-gain by array-based comparative genomic hybridization were concordant by array-based comparative genomic hybridization. The sensitivity and specificity of the fluorescence in situ hybridization assay was 80% and 95%, respectively (P=0.02). The sample with the highest level of amplification by array-based comparative genomic hybridization (log₂ratio=3.6) also scored highest by fluorescence in situ hybridization (ratio=8.2). There was a correlation between the expression of JAK2 and amplification status (Mean 633 vs 393, P=0.02), and there was a trend of association with PD-L1 RNA expression (Mean 46 vs 22, P=0.11). No significant association was observed between PD-L1 immunohistochemistry expression and copy-number gain status. In summary, the novel array-based comparative genomic hybridization assay for detection of chromosome 9p24.1 strongly correlates with the detection of copy-number gain by array-based comparative genomic hybridization. In triple negative breast cancer, this biomarker may identify a relevant subset of patients for targeted molecular therapies.