Deep penetrating naevus: clinicopathological study of 31 cases with further delineation of histological features allowing distinction from other pigmented benign melanocytic lesions and melanoma

Superficial Wnt-Activated Melanocytic Nevi/Melanocytomas With a Junctional Component: A Case Series

ABSTRACT

The conventional morphological characteristics of Wnt-activated deep penetrating/plexiform melanocytomas/nevi (DPN) are those of large spindled or epithelioid melanocytes with distinctive voluminous amphophilic cytoplasm, fine pigmented granules, and surrounding melanophages. The central molecular hallmark is the activation of the Wnt-pathway predominantly driven by mutations in the beta-catenin ( CTNNB1 ) gene. Although typically lacking a junctional component, a lesser-known superficial variant with a junctional component has been identified, which could potentially lead to diagnostic challenges. This study presents a cohort of 11 such cases displaying a junctional component of DPN from 10 patients (5 women and 5 men; age range: 27-78 years; median age: 51 years). The nevi were distributed as follows: 1 conjunctival, 1 scalp, 2 lower limb, and 6 truncal lesions. Eight cases were combined with a conventional nevus, 2 cases displayed pure DPN cytology exhibiting only a junctional element, and 9 cases exhibited some degree of lentiginous architecture. All cases demonstrated a low mitotic index (<1 mitosis/mm 2 ). Immunohistochemistry revealed positive BRAF V600E staining in 8 cases (8/11), whereas all cases tested (11/11) were PRAME negative. Nuclear beta-catenin and LEF1 staining was consistently strong and diffuse with DPN cytology (11/11), along with robust cyclin D1 staining in all cases tested (11/11). By contrast, all 9 conventional nevi showed an absence of nuclear beta-catenin staining (0/9) and weaker, mosaic-type LEF1 and cyclin D1 staining was observed. This study emphasizes the diagnostic challenge these nevi can pose in the absence of a conventional, deeper DPN component, which can potentially be misdiagnosed as melanoma.

Combined WNT-activated deep-penetrating/plexiform melanocytoma: insights into clinicopathological and molecular characterization

BACKGROUND

A combined deep-penetrating tumour redefined as WNT-activated deep-penetrating/plexiform melanocytoma (DPM), may pose challenging clinical and histological diagnoses.

OBJECTIVES

To review the clinicopathological characteristics of combined DPMs and characterize the molecular profile of atypical and malignant forms.

METHODS

The study included 51 patients with combined DPMs diagnosed at the Hospital Clinic of Barcelona and the University of Florence between 2012 and 2020. Clinical data, dermoscopy images (when available) and histological characteristics were reviewed. Immunohistochemistry for β-catenin, LEF1, HMB45, Ki67, p16 and PRAME (preferentially expressed antigen in melanoma) was performed. Atypical forms underwent next-generation sequencing (NGS) panel analysis, including driver genes implicated in DPMs, TERT-promoter (p) mutations and the investigation of the 9p21 locus via fluorescence in situ hybridization.

RESULTS

Among the 51 patients (32 females and 19 males, age range 4-74 years), 68% with available clinical data (15/22) were initially suspected of having melanoma. Except for one patient, complete excision resulted in no recurrences or metastases. One patient who had an incompletely excised combined DPM developed a lymph node melanoma metastasis 10 years later. In the 51 patients, 10 samples (20%) showed atypical histological features; 7 (14%) exhibited a significant loss of p16 expression; and 2 (4%) showed a high-proliferative index (Ki67 over 5%). NGS analysis in 11 patients revealed a double mutation BRAFV600E and exon 3 CTNNB1; no TERTp mutations were detected.

CONCLUSIONS

Clinical suspicion of melanoma is common in combined DPMs, but malignant progression is infrequent in tumours lacking high-grade atypia or proliferation. These findings are congruent with the consideration of these lesions as intermediate-grade tumours or melanocytomas.

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.

Towards diagnostic criteria for malignant deep penetrating melanocytic tumors using single nucleotide polymorphism array and next-generation sequencing

Cutaneous deep penetrating melanocytic neoplasms frequently simulate melanoma and might occasionally progress to metastatic melanoma. Distinguishing deep penetrating nevi (DPN) and deep penetrating melanocytomas (DPM) from malignant deep penetrating tumors (MDPT) is difficult based on histopathology alone, and diagnostic criteria for MDPT are currently lacking. Using a molecular workup, we aimed to provide readily available diagnostic tools for classification of deep penetrating tumors. We used clinical follow-up and Single Nucleotide Polymorphism (SNP) array for tumor classification of 20 deep penetrating neoplasms to identify associations with histopathological, immunohistochemistry, and NGS findings. Ten neoplasms were classified as MDPT, four as DPM, and six as DPN. Two MDPT showed metastases. The following parameters were statistically significantly associated with MDPT: severe nuclear atypia (risk ratio [RR] 2.9, p < 0.05), absence of a nevus component (RR 10.0, p = 0.04), positive PRAME expression (RR 9.0, p = 0.02), complete loss of p16 expression (RR 3.5, p = 0.003), TERT-p and APC mutations (RR 11.0, p = 0.01 and RR 2.7, p = 0.002, respectively), and ≥1 additional pathogenic mutation (RR 9.0, p = 0.02). Ki-67 expression ≥ 5% was not significantly associated with MDPTs, although it was <5% in all DPNs. Three MDPT did not show nuclear β-catenin expression despite having a CTNNB1 (n = 2) or an APC mutation (n = 1). Our findings suggest that complete loss of p16 and positive PRAME expression, a driver mutation in APC, ≥ 1 additional pathogenic mutation, especially in TERT-p, support an MDPT diagnosis in deep penetrating neoplasms. Besides severe nuclear atypia and possibly severe inflammation, we did not identify specific histopathological criteria for malignancy. Non-aberrant nuclear β-catenin expression might not exclude a deep penetrating signature in MDPT.

Conventional and Atypical Deep Penetrating Nevus, Deep Penetrating Nevus-like Melanoma, and Related Variants

Simple Summary

Atypical deep penetrating nevus (DPN) is a unique skin tumor with an uncertain biologic/metastatic potential that may be difficult to distinguish from DPN (an indolent lesion) and DPN-like melanoma (an aggressive lesion) based on the results of histomorphologic analysis and commonly employed molecular studies such as fluorescence in situ hybridization and comparative genomic hybridization alone. Herein, we review the clinical, histomorphological, immunohistochemical, molecular, and cytogenetic characteristics of the DPN spectrum of lesions to try to better understand the prognosis of these lesions and possible treatment approaches.

Abstract

Deep penetrating nevus (DPN) is an uncommon acquired melanocytic lesion with a distinct histopathological appearance that typically behaves in an indolent manner. The lesion is characterized by a symmetrical proliferation of epithelioid to spindled melanocytes associated with abundant melanophages and wedge-shaped extension to the deep reticular dermis and subcutis. Pronounced cytologic atypia and mitotic figures are usually absent, which helps distinguish DPN from melanoma with a deep penetrating growth pattern. Recently, the concept of atypical DPN has been proposed for lesions that demonstrate borderline histomorphologic features and may be associated with lymph node deposits but lack the copy number aberrations typical of melanoma by either fluorescence in situ hybridization or comparative genomic hybridization. While most of these lesions have a favorable clinical course, rare lesions may progress to melanoma. In this review, we summarize the current literature on atypical DPNs with uncertain behavior/metastatic potential and outline the characteristics that distinguish these lesions from conventional DPN and melanoma with DPN-like features.

NGS-Based Analysis of Atypical Deep Penetrating Nevi

Simple Summary

The recent WHO classification of melanocytic tumors requires the implementation of combined phenotypic–genotypic diagnostics. For rare tumors, such as atypical deep penetrating nevi, there is insufficient information regarding genetic status, and it is not yet clear whether the observed unusual morphological cyto-architectures reflect a distinct genomic profile or are associated with an increased metastatic potential and aggressive clinical behavior. We report herein a comprehensive next-generation sequencing (NGS) analysis of a series of atypical DPNs, showing their mutational profile with some specific signatures for these rare and diagnostically challenging tumors.

Abstract

Deep penetrating nevi (DPNs) are rare melanocytic neoplasms consisting of pigmented spindled or epithelioid melanocytes with a distinctive wedge-shaped configuration showing activation of the WNT pathway, with unusual cyto-architectural features. It is unclear whether they show a distinct genomic profile associated with a diverse metastatic potential. We describe herein a cohort of 21 atypical DPNs analyzed by next-generation sequencing using the Ion AmpliSeq™ Comprehensive Cancer Panel. We found that β-catenin exon 3 was mutated in 95% and MAP kinase pathway genes in 71% of the cases. Less frequent mutations were observed in HRAS (19%) and MAP2K1 (24%). Isocitrate dehydrogenases 1 (IDH1) mutations, including R132C, V178I, and S278L, were identified in 38% of cases and co-existed with BRAF/HRAS mutations. The only case with progressive nodal disease carried alterations in the β-catenin pathway and mutations in IDH1 and NRAS (codon 61). By a comprehensive mutation analysis, we found low genetic heterogeneity and a lack of significant associations between specific gene mutations and histopathological features, despite atypical features. Whether the acquisition of an NRAS or IDH1 mutation in an atypical DPN may represent a molecular evolution implying a pathway to melanoma progression should be confirmed in a larger series.

Melanocytic lesions with blue naevus-like (dendritic) morphology: an update with an emphasis on histopathological, immunophenotypic, and molecular features

An accurate diagnosis of melanocytic lesions requires a thorough histopathological evaluation accompanied by appropriate correlation with clinical examination findings. Although most melanocytic lesions can readily be classified as one of the defined diagnostic entities according to well-established diagnostic criteria, a subset of melanocytic lesions, particularly those with blue naevus-like (pigmented dendritic) morphology, have notoriously constituted an enduring challenge for pathologists. These lesions are rare and often show histological ambiguities, with features of both benignity and malignancy, thereby making accurate risk assessment and prediction of their biological behaviours difficult on histological grounds alone. Herein, we outline a practical and systematic approach for the diagnosis of melanocytic lesions with dendritic morphology, with a particular focus on histological and immunophenotypic features that help to distinguish one entity from another. In this review, we provide the most current knowledge on these melanocytic lesions in the literature and our experience with these rare entities, and we discuss the utility of molecular techniques as an ancillary tool, especially in histologically ambiguous and/or borderline lesions.

Combination of Congenital and Deep Penetrating Nevus by Acquisition of β-Catenin Activation

Deep penetrating nevus (DPN) is an intradermal, sometimes compound benign melanocytic lesion, which involves the reticular dermis, occasionally reaching the subcutis, which can raise concern for melanoma both clinically and histologically. Recently, it has been genetically defined by the combination of MAPK activating and β-catenin activating mutations. We sought to investigate genetic alterations in 2 cases of combined nevi of congenital melanocytic and DPN. Case 1 was a 16-year-old woman with a pigmented lesion on the trunk since birth, which was completely excised. Histopathological examination revealed a combined congenital nevus with a DPN. Comparative genomic hybridization showed no major genetic alterations, except for gain of 6q11.1 and point mutation of B-RAF V600E. Case 2 was a 62-year-old woman with a congenital pigmented lesion on the back. The lesion was diagnosed as a combined nevus of congenital and DPN. Comparative genomic hybridization showed no genetic alterations, and the NRAS Q61K was detected in both components. DPN is in most cases part of a combined nevus. Our cases showed strong and uniform nuclear expression of β-catenin and cyclin D1 in the DPN component suggesting the evolution of the congenital nevus to the DPN clone by acquiring β-catenin activating mutation.

Deep Penetrating Nevus and Borderline-Deep Penetrating Nevus: A Literature Review

Deep penetrating nevi (DPN) are rare melanocytic nevi, which can exhibit atypical histological features hampering the differentiation from malignant melanoma. DPN are considered benign melanocytic lesions, but rare spread to lymph nodes and unfavorable clinical outcomes associated with borderline/atypical DPN (B-DPN) has been reported. Since no guidelines are available for DPN and B-DPN, we aimed to review the literature on DPN and B-DPN to assess the management and prognosis. We screened 3,513 references from EMBASE, Scopus and Medline databases, and included 15 studies with a total of 355 DPN patients and 48 B-DPN patients. Therapeutic interventions ranged from simple excision to wide excisions and sentinel lymph node biopsy (SLNB), with block lymph node dissection in some positive SLNB cases. Follow-up periods ranged from 3 months to 23 years during which a total of five recurrences, two in DPN and three in B-DPN group, and three metastases, in B-DPN group, were reported. While some of the included studies comprised clinical and histopathological correlation, few included genetic assessment. The present review highlights the need for prospective cohort studies applying composite measures to identify effective regimens of diagnostic workup and treatment in DPN and B-DPN.

Common and not so Common Melanocytic Lesions in Children and Adolescents

The acquired melanocytic nevus is the most common lesion encountered by pediatric pathologists and dermatopathologists in their daily practice. In most cases, there are few difficulties in histopathologic diagnosis. However, it is the acquired melanocytic lesion known as the Spitz nevus, with its intrinsic atypical features which becomes the challenge since it exists along a histopathologic and biologic continuum from the atypical Spitz tumor to spitzoid melanoma. The frustration with some of these spitzoid lesions is that even the "experts" cannot agree as to the differentiation of one from the other even at the level of molecular genetics. Other melanocytic lesions are discussed including the congenital melanocytic nevus with its proliferative nodule(s) and melanoma as the ultimate complication. Although uncommon, cutaneous melanoma in the first 2 decades is emerging as a clinical problem especially in young women in the second decade of life. These are ultraviolet-associated neoplasms whose histopathologic and prognostic features are identical to the adult experience. Considerable progress has been made over the past 15 to 20 years in our understanding of cutaneous melanocytic lesions, but gaps still exist in the important group of spitzoid lesions. It can also be anticipated that more cutaneous melanomas in children will be seen in the future based upon epidemiologic studies.

Multiple Oral Deep Penetrating Nevi Extending to the Masseter and Buccal Fat Pad

The deep penetrating nevus (DPN) is a rare benign melanocytic tumor often clinically and histopathologically mistaken for malignant melanoma (MM) and other nevus types. This report describes an extremely rare case of multiple lesions of a large DPN in the oral cavity with extensive infiltration to the minor salivary gland, buccal fat pad, buccinators, and masseter muscles, yet with preservation of the normal anatomic architecture. After receiving a diagnosis of MM in another hospital, the patient was at risk for receiving a wide excision that included the masticatory muscles, facial nerve, and overlying skin. Histopathologically, distinct cellular properties were completely masked with heavy pigmentation, thus precluding a proper distinction of benignity versus malignancy. The proliferative capacity of the tumor was analyzed further by immunohistochemistry of bleached tissue sections and tumor behavior was indirectly evaluated by insufficient tumor stromal interaction, with the conclusion that the specimen was benign. Conservative surgery was limited to the oral cavity. Multiple DPNs in the oral cavity merit attention because of the high risk of being mistaken for MM, which would require a wider surgical excision of the head and neck region.

The deep penetrating nevus

The deep penetrating nevus (DPN), also known as the plexiform spindle cell nevus, is a pigmented lesion that commonly arises on the head and neck in the first few decades of life. Histopathologically, the DPN is wedge-shaped and contains melanocytes that exhibit deep infiltration into the dermis. Given these features, DPN may clinically and histopathologically mimic malignant melanoma, sparking confusion about the appropriate evaluation and management of these lesions. The goal of this review is to summarize the clinical and histopathological features of DPN and to discuss diagnostic and treatment strategies for dermatologists.

Proliferative activity, chromosomal aberrations, and tumor-specific mutations in the differential diagnosis between blue nevi and melanoma

Blue nevi are a clinically and pathologically heterogeneous group of benign pigmented dermal melanocytic tumors that may exhibit histologic overlap with malignant melanoma. This study evaluates the role of immunohistochemical and molecular analyses in the classification and differential diagnosis between blue nevi and melanoma. Twenty-three dermal melanocytic tumors, initially diagnosed as benign or ambiguous, were subjected to immunohistochemical staining for phosphohistone H3 and MIB-1 to evaluate mitotic activity, comparative genomic hybridization to detect chromosomal aberrations, and GNAQ, GNA11, BRAF, NRAS, and KRAS sequencing. Of 19 patients with follow-up information (median, 1.6 years), 3 developed recurrent or metastatic disease. Nevertheless, 11 of the 19 patients with follow-up had <2 years of follow-up. Nine of 23 patients showed chromosomal aberrations, including all 3 patients with tumor recurrence or progression. There was no significant correlation between mutation status (P = 0.6) or mitotic rate (P = 0.3) and outcome. In conclusion, three of nine patients with chromosomal aberrations developed tumor recurrence or progression. Patients with histologically ambiguous dermal melanocytic proliferations that exhibit copy number aberrations should undergo careful clinical follow-up.

Deep Penetrating Nevus: A Review

Context.—Deep penetrating nevus is a distinctive melanocytic lesion that may simulate melanoma both clinically and histologically.

Objective.—To review clinical and histologic features of deep penetrating nevi and discuss their differential diagnosis, especially regarding melanoma.

Data Sources.—The literature on deep penetrating nevi is reviewed and supplemented by our experiences with deep penetrating nevi.

Conclusions.—One or more disturbing histologic features may frequently be found in deep penetrating nevi, including asymmetry, plump but fairly regular nests of melanocytes in the dermis, cytologic atypia with some nuclear pleomorphism, a small to medium-sized eosinophilic nucleolus, absence of maturation, occasional presence of normal dermal mitoses, and a patchy mononuclear inflammatory cell infiltrate. Although unusual, such histologic features should not be regarded as a sign of malignancy in deep penetrating nevi.

Spindle cell melanocytic lesions: part II—an approach to intradermal proliferations and horizontally oriented lesions

Melanocytic lesions show great morphological diversity in their architecture and the cytomorphological appearance of their composite cells. Whereas functional melanocytes show a dendritic cytomorphology and territorial isolation, lesional nevomelanocytes and melanoma cells typically show epithelioid, spindled or mixed cytomorphologies, and a range of architectural arrangements. Spindling is common to melanocytic lesions, and may either be a characteristic feature or a divergent appearance. The presence of spindle cells may mask the melanocytic nature of a lesion, and is often disconcerting, either due to its infrequent appearance in a particular lesion or its interpretation as a dedifferentiated phenotype. Spindle cell melanocytic lesions follow the full spectrum of potential biological outcomes, and difficulty may be experienced judging the nature of a lesion due to a lack of consistently reliable features to predict biological behaviour. Over time, recognition of numerous histomorphological features that may portend a more aggressive lesion have been identified; however, the translation of these features into a diagnostic entity requires a gestalt approach. Although most spindle cell melanocytic lesions may reliably be resolved through this standard approach, problem areas do exist for the surgical pathologist or dermatopathologist. With this review (part II of II), we complete our discussion of spindle cell melanocytic lesions, in order to: (1) model a systematic approach to such lesions; and (2) provide familiarity with those melanocytic lesions which either typically or occasionally display a spindled cytomorphology.

State of the art, nomenclature, and points of consensus and controversy concerning benign melanocytic lesions: outcome of an international workshop

The following communication summarizes the proceedings of a one-day International Workshop focusing on the histology of benign melanocytic nevi. Areas of controversy identified in 6 focus sessions were the nomenclature and relationships among common nevi including nevi with halo reactions, traumatized nevi, "dysplastic" nevi, and nevi from particular anatomic sites; developmental biology and frequency of malignant transformation associated with congenital nevi; the characterization and biologic nature of atypical spitzoid neoplasms; the basic definition of particular melanocytic cellular phenotypes, and the nomenclature and biologic nature of many candidate blue nevi, combined nevi, and other controversial lesions such as deep penetrating nevus and pigmented epithelioid melanocytoma. Concentrated data collection and follow-up, molecular characterization, and future consensus Workshops may facilitate the resolution of some of these problems. The Group recommended the description of ambiguous or "borderline" lesions as tumors with indeterminate or uncertain biologic/malignant potential. The participants also advised that such lesions at a minimum should be managed by complete excision with clear surgical margins.

Pigmented lesion pathology: what you should expect from your pathologist, and what your pathologist should expect from you

The first part of this review examines the reliability of histologic diagnosis in pigmented lesions, as measured by concordance studies and medicolegal analysis. It emphasizes the role of clinicians in maximizing that reliability, by providing adequate clinical descriptions, using appropriate biopsy technique, and critically interpreting pathology reports. It identifies those entities that are especially problematic, either because they cannot be reliably recognized by the histopathologist or because their histology is a poor guide to their biologic behavior. The second part of the review is a guide to some of the more difficult and controversial pigmented lesions, including dysplastic nevus, spitzoid nevi and melanomas, cellular blue nevus, animal-type melanoma, and deep penetrating nevus.

Ataxia telangiectasia-mutated gene is a possible biomarker for discrimination of infiltrative deep penetrating nevi and metastatic vertical growth phase melanoma

The deep penetrating nevus (DPN) is a variant of benign melanocytic nevus with clinical and histologic features mimicking vertical growth phase, nodular malignant melanoma (NMM). Because fatal misdiagnosis such as NMM occurs in 29% to 40% of the DPN, molecular differentiation markers are highly desirable. Beyond the clinical demand for precise diagnosis and diagnosis-adapted, preventive therapeutic strategies, the DPN represents a valuable natural model for melanocytic invasion without metastatic potential that per se deserves further investigations. In the present study, at first, we used a genome-wide, microarray-based approach to systematically prescreen for possible molecular markers differentially expressed between selected cases of typical DPN (n=4) and metastatic NMM controls (n=4). Gene expression profiling was done on Affymetrix Human X3P microarrays. Of the 47,000 genes spotted, we identified a list of 227 transcripts, which remained significantly regulated at a false discovery rate of 5%. Subsequently, we verified the expression of a subset of the most interesting transcripts in a larger immunohistochemical series (DPN, n=17; NMM, n=16). Of these transcripts, three were selected for immunohistochemical confirmation: tissue inhibitor of metalloproteinase-2, tumor protein D52, and ataxia telangiectasia-mutated gene (ATM). Additional criteria for selection from the list of 227 significantly regulated transcripts were grouping into functional Ingenuity networks and a known melanoma- or cancer-relevant function. Following these criteria, we detected a highly significant up-regulation of ATM transcription in NMM, which was also mirrored by ATM protein up-regulation. In contrast to the other markers, ATM particularly might serve as a suitable diagnostic and reliable discriminator of DPN/NMM because ATM immunoreactivity also showed a reliable staining consistency within all samples of both entities.

[Epithelioid and hyperpigmented melanocytic tumors. An overview]

Spindle cell and epithelioid cell differentiation occur in both benign and malignant hyperpigmented melanocytic lesions. Reed nevus is characterized by compact, sharply circumscribed junctional cellular nests composed of slender hyperpigmented melanocytes shaped like spindle cells. Deep penetrating nevus is characterized by a diffuse dermal proliferation composed of small nests and fascicles of pale ovoid and epithelioid melanocytes. Cellular blue nevi often have a characteristic hourglass or dumbbell shape, with sharply circumscribed elongated nests and fascicles of pale, densely layered ovoid melanocytes and adjacent melanophages. Epithelioid blue nevus is characterized by large epithelioid melanocytes with abundant cytoplasm and melanin often concentrated to some degree in the cell membrane. Animal-type melanoma is a particularly hyperpigmented variant of melanoma in which large melanophages predominate and there are varying proportions of melamin-rich spindle-shaped and large atypical epithelioid melanocytes. Morphologically, pigmented epithelioid melanocytoma combines characteristics of both animal-type melanoma and pigmented epithelioid nevus. Malignant melanoma may occur in conjunction with a preexistent blue nevus. Malignant blue nevus is now regarded as a malignant melanoma mimicking a blue nevus in structure and pattern. It is therefore of paramount importance to view multiple mitoses within a cellular blue nevus-like proliferation as an alarm signal as they are usually indicators of a malignant melanoma.

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.

Deep penetrating nevus of cheek skin

Deep penetrating nevus is a cutaneous pigmented lesion first reported by Seab et al. in 1989. The skin of the face and neck region is one of the most common sites for deep penetrating nevus. Despite this prevalence in the head and neck region, deep penetrating nevus has not previously been discussed in journals emphasizing oral and maxillofacial pathology. The purpose of this case report is to present this rare entity to the oral pathology community, emphasizing its common presenting histologic features of a combined nevus.

Melanocytic “ball-in-mitts” and “microalveolar structures” and their role in the development of cellular blue nevi

To test the hypothesis of whether cellular blue nevi (CBN) may originate from "ordinary" compound and dermal nevi, a total of 275 melanocytic nevi including 59 CBN, 34 ordinary blue nevi, 87 combined nevi (including 43 so-called clonal nevi), 35 deep penetrating nevi, and 60 ordinary compound and dermal nevi (30 of each) were studied for the presence of so-called ball-in-mitts and microalveolar structures. A ball-in-mitts structure was defined as a single centrally placed melanocyte with a round to oval nucleus (the "ball" cell) and a clear, dusty, or pigmented cytoplasm encircled by a single dendritic cell (the "mitt" cell) with an oval to spindle-shaped nucleus and slender bipolar processes containing melanin and surrounding at least one fourth of the ball's diameter. A microalveolar structure was defined as a group of 2 to 10 centrally placed melanocytes with round to oval nuclei and clear, dusty, or pigmented cytoplasm (balls) surrounded by one or more cells (mitts) with spindle-shaped nuclei and slender bipolar processes containing melanin. Microscopically, ball-in-mitt and microalveolar structures were detected in all types of nevi studied, with the highest incidence in combined nevi (82%), CBN (76%), and ordinary "nonblue" nevi (73%). In CBN, ball-in-mitts and microalveolar structures tended to be located in the deeper portion of the lesions, whereas in ordinary nonblue nevi, they were most often found superficially, just below the epidermis; in clonal nevi, these structures were often confined to the "clonal" parts. Immunohistochemically, ball-in-mitts and microalveolar structures were positive for HMB45. Ultrastructurally, the balls tended to have round to oval nuclei, whereas the mitts possessed oval, elongated to spindled nuclei. Melanosomes were found in various stages in the cells of both structures. The cytoplasm of the mitts typically formed elongated polar processes, sometimes with club-like widenings at the ends, completely or partially encircling the balls. In the microalveolar structures, the adjacent cells forming the mitts surrounded the ball cells like a chain. Our study suggests that some or even most cases of CBN may evolve from ordinary nonblue nevi. This process may involve several steps and is probably reflected by the appearances of combined nevi, deep penetrating nevi, and CBN. These nevi often show a morphological overlap, and ball-in-mitts and microalveolar structures found in various stages of their development seem to greatly account for this overlap.

Sentinel Lymph Node Biopsy for Atypical Melanocytic Lesions with Spitzoid Features

INTRODUCTION

Sentinel lymph node biopsy (SLNB) is routinely used as a staging procedure for melanomas, however may also assist in understanding the biology of atypical and controversial spitzoid melanocytic skin lesions.

METHODS

Five hundred and forty-nine sentinal lymph node excisions were performed over a 5-year period. Fourteen patients with controversial melanocytic lesions were identified and of these ten underwent SLNB. The histology of the primary skin lesion and corresponding sentinal lymph nodes were evaluated and correlated with outcome.

RESULTS

Thickness of the primary melanocytic lesion ranged from 1.22 to 4 mm. Fifty percent of patients were less than 17 years of age. Ten patients underwent SLNB and three cases (30%) displayed metastatic disease in the SLNB specimen. All three patients were under 17 years of age and all underwent completion axillary dissection. One completion axillary dissection had an additional node with metastasis on routine H&E and immunohistochemical staining. No capsular invasion was seen. All three cases with metastatic disease received adjuvant systemic therapy and remain disease free at 29, 49 and 57 months follow-up. All patients with a negative SLNB remain disease free at mean follow-up of 28.1 months (range: 13-40 months).

CONCLUSION

Our results confirm that some of these spitzoid lesions metastasize to regional lymph nodes and SLNB is a valuable adjunct tool in staging these lesions. However, molecular studies and a prolonged follow-up are needed to determine whether these lesions, especially those occurring in children are comparable to stage matched overt melanoma in adults.

Loss of dipeptidyl peptidase IV immunostaining discriminates malignant melanomas from deep penetrating nevi

The deep penetrating nevus is a rare variant of benign melanocytic nevus with histologic features mimicking vertical growth phase, nodular malignant melanoma. In this study, we expand on the search for new complementary discriminating markers by analyzing a selection of both cell cycle-related factors, such as retinoblastoma protein and phospho-retinoblastoma protein Ser795 as indicators for retinoblastoma protein activation/inactivation status, and invasion-related factors, such as matrix metalloproteinase-1, matrix metalloproteinase-2, membrane-type matrix metalloproteinase-1 and integrin beta3. MIB-1/Ki-67 was analyzed as an example for a common proliferation marker. Dipeptidyl peptidase IV/CD26 was analyzed as a marker affecting both proliferation and invasion of malignant melanocytic tumors. Semiquantitative assessment of both immunolocalization and immunoreactivity of retinoblastoma protein and phospho-retinoblastoma protein Ser795, MIB-1/Ki-67, matrix metalloproteinase-1, matrix metalloproteinase-2, membrane-type matrix metalloproteinase-1 and integrin beta3 revealed no consistent differences between deep penetrating nevi (n=14) and matched cases of nodular malignant melanomas (n=10). Matrix metalloproteinase-1 and matrix metalloproteinase-2 immunostaining of some deep penetrating nevi even exceeded that of nodular malignant melanomas. Membrane-type matrix metalloproteinase-1 expression scores of nodular malignant melanomas were higher than those of deep penetrating nevi, which was, however, not significantly discriminative. In contrast, immunostaining of dipeptidyl peptidase IV was significantly discriminative due to a consistent lack of dipeptidyl peptidase IV-expression in nodular malignant melanomas. These results add evidence that among the selected markers supposed to be relevant for melanoma progression the presence of dipeptidyl peptidase IV can be used to support diagnosis of deep penetrating nevi in doubtful cases. As loss of dipeptidyl peptidase IV may also be causally linked to the transition of invasive to metastatic phenotypes, the molecular mechanisms downstream of dipeptidyl peptidase IV deserve to be studied in more detail in future investigations.

Deep penetrating nevus: a case report and brief literature review

Background -

Deep penetrating nevus (DPN) is a distinct variant of melanocytic nevus and remains a histopathologic challenge to pathologists because of its resemblance to blue nevus, malignant melanoma, pigmented Spitz nevus, and congenital melanocytic nevus. It often goes unrecognized due to its relative rarity.

Case presentation -

Here we report a case of DPN of the left anterior leg in a 51-year old female. A brief review of the literature shows that these lesions have a distinct growth pattern and cellular morphology that can differentiate these lesions from other entities including malignant melanoma.

Conclusion -

It is important to recognize these features because DPN carries a better prognosis than malignant melanoma.

Pigment synthesizing melanoma (so-called animal type melanoma): a clinicopathological study of 14 cases of a poorly known distinctive variant of melanoma

AIMS

Pigment synthesizing melanoma (so-called animal type melanoma) (PSM) is a rare histopathological variant of melanoma so termed because of prominent melanin production and its similarity to a variant of melanoma seen in grey horses. The aim of this study was to report the clinicopathological characteristics of 14 cases of animal type melanoma.

METHODS AND RESULTS

Six patients were female and eight were male with ages ranging from 5 to 52 years (mean 31 years, median 39 years). The head and neck represented the most common site. The clinical diagnosis was of melanoma in seven cases, blue naevus in three cases, benign naevus in three cases and a pigmented basal cell carcinoma in one case. The histological diagnosis of PSM was predicated on the basis of an asymmetrical, predominantly intradermal tumour formed of deeply pigmented, round or short, spindle-shaped dendritic melanocytes with some degree of hyperchromatism and a single nucleolus. Cytological atypia was always present but was not pronounced. A prominent population of macrophages was invariably present. Four tumours were compound and 10 tumours were predominantly intradermal. The mitotic count was usually low, ranging from 1 to 5 per 10 high-power fields (mean 2). Perineural and lymphovascular invasion was not seen. The Breslow thickness ranged from 1.1 to 7.5 mm (mean 3.3 mm). Follow-up was available in 13 patients. The median follow-up period was 5 years. Six patients had no recurrence, three had local recurrence in the form of satellite nodules adjacent to the scar, four had spread to the regional lymph nodes and one patient had distant metastases to the liver. There were no deaths.

CONCLUSIONS

This study demonstrates that PSM is a distinctive, possible low-grade variant of melanoma usually lacking the histological features predictive of aggressive behaviour seen in ordinary melanoma. It should be managed in the same way as other melanomas with wide local excision.

Combined naevus: a benign lesion frequently misdiagnosed both clinically and pathologically as melanoma

BACKGROUND

Combined naevi are characterised pathologically by the presence of two or more different types of melanocytic naevi in a single lesion. They are prone to clinical and pathological misdiagnosis as melanoma. Misdiagnosis may result in inappropriate treatment, patient anxiety and medicolegal consequences.

AIMS

With the aim of reducing the incidence of misdiagnosis, this study documents the clinical and pathological features of a large series of combined naevi and describes how to distinguish them from melanoma.

PATIENTS AND METHODS

The slides of skin lesions from 220 patients that were coded as combined naevus between 1990 and 2001 were retrieved from the archival files of the Department of Anatomical Pathology, Royal Prince Alfred Hospital, Sydney, Australia. The clinical notes, letters from referring pathologists (for consultation cases) and slides were reviewed and for each lesion clinical and pathological features were assessed. Thirty-eight cases were excluded either because they included only one naevus component or because there were atypical pathological features in the slides available for review. The remaining 182 cases formed the study population.

RESULTS

The patients included 92 females and 87 males (1.1:1). In three cases the gender was not known. Mean and median patient ages were 29.6 and 28 years, respectively. The anatomical site of involvement was the trunk in 64 cases (35.2%), head and neck region in 43 cases (23.6%), upper extremity in 40 cases (22.0%), lower extremity in 18 cases (9.9%) and perineum and buttock region in eight cases (4.4%). In nine cases the site of involvement was not known. A pre-operative clinical diagnosis was recorded in 126 cases; of these, melanoma was suspected clinically in 33 cases (26.2%) while combined naevus was diagnosed clinically in only three cases (2.4%). Histologically, 180 cases included two different naevus components, and in two cases three different naevus components were present. The most common combination was a common acquired naevus of compound type associated with a blue naevus of deep penetrating naevus type; this occurred in 57 cases (31.3%). The referring pathologist recorded a preferred diagnosis in 88 of 122 consultation cases; of these, melanoma was suspected in 23 cases (26.1%) and in 23 cases combined naevus was favoured (26.1%).

CONCLUSIONS

Combined naevus is an uncommon type of melanocytic naevus that is frequently misdiagnosed both clinically and pathologically. Knowledge and recognition of the pathological features of combined naevi and the important features that distinguish them from melanomas should reduce the frequency of misdiagnosis.