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

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.

Pigmented Epithelioid Melanocytomas and Their Mimics; Focus on Their Novel Molecular Findings

Simple Summary

Pigmented epithelioid melanocytoma (PEM) is a rare entity with a controversial biological behavior. Some of these tumors behave in an indolent manners while others can locally spread. Herein, we review the clinical presentations, the pathological features as well as the genomic signatures associated with this rare entity. We also report an example of a challenging case of PEM that we encountered and show how usage of novel molecular diagnostic techniques focusing helps addressing this diagnostic conundrum.

Abstract

Pigmented epithelioid melanocytoma (PEM) is a unique tumor with significantly pigmented appearance and indolent behavior; however, it can demonstrate cytological atypia and metastasize to local lymph nodes. Clinical and histomorphological overlap between PEM and its lower or higher-grade mimics can make it difficult to distinguish in certain cases. Genomic, transcriptomic and epigenetic data indicate that PEMs are molecularly distinct entities from other melanocytic neoplasms and melanomas. In addition, methylation studies are emerging as a tool that can be useful in difficult cases. In this review, we focus on the clinical, histopathologic and recent insights in the molecular features of pigmented epithelioid melanocytic melanocytomas and their mimics. We also present a challenging case that was resolved using methylation analysis providing a proof of concept for using epigenetic studies for similar challenging cases.

A Blue-pigmented Lesion on the Cheek in a Three-year-old Girl: A Quiz

Abstract is missing (Quiz)

"Animal-Type Melanoma/Pigmented Epithelioid Melanocytoma": History and Features of a Controversial Entity

Animal-type melanoma (ATM) was first described in the literature by Levene in 1979 in relation to a patient with a characteristic clinical presentation, and only later, rare and anecdotal case series have tried to shed light on an entity that has undergone several nosographic classification changes, and which, since 2018, is classified under the term "pigmented epithelioid melanocytoma". Here, we conduct a brief review of the current literature on ATM and present a new clinical case with histopathological, immunophenotypic, and molecular investigations.

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.

Genomic and Clinicopathologic Characteristics of PRKAR1A-inactivated Melanomas: Toward Genetic Distinctions of Animal-type Melanoma/Pigment Synthesizing Melanoma

Melanocytic tumors with inactivation of protein kinase A regulatory subunit-α (PRKAR1A) have large oval nuclei and intense pigmentation. Historically, these tumors have been categorized under various names, including epithelioid blue nevus, pigmented epithelioid melanocytoma (PEM) and animal-type melanoma. Although a subset of PEM harbor BRAF activating mutations and biallelic inactivation of PRKAR1A, there are only a few reports of melanomas, or of tumors with genomic alterations beyond those of PEMs. Herein, we describe the clinicopathologic and genetic features of 8 melanomas and tumors that lack PRKAR1α expression by immunohistochemistry but do not fit with conventional PRKAR1A-inactivated melanocytomas. These tumors tended to affect younger patients than conventional melanomas (median age=38 y) and presented as dark brown/black papules and nodules. Histopathologically, they demonstrated nodularity, sometimes in a background of conventional melanoma, and large vesicular nuclei with prominent nucleoli. With the exception of 1 case, the mitotic index was not significantly elevated. Immunohistochemically, all cases showed loss of PRKAR1α and of p16 expression. Seven tumors underwent massively parallel short read (next-generation) sequencing of a panel of 480 cancer-associated genes. Five tumors demonstrated truncating mutations of PRKAR1A and the 2 in which such mutations were not identified demonstrated loss of heterozygosity of the PRKAR1A locus. Four of the tumors harbored BRAF V600E mutations, and 1 harbored a FAM39B-BRAF gene fusion. Another harbored a GNA11 activating mutation. A MAP kinase activating mutation was not identified in the remaining case. Four tumors displayed TERT promoter mutations and chromosomal copy number changes supporting the diagnosis of melanoma. Two cases without these alterations and were classified as "high-grade PRKAR1A-inactivated melanocytomas". The 1 case with widespread metastases demonstrated mutations in TP53 and RB1. Overall, we provide the first genetic characterization of PRKAR1A-inactivated melanomas, discuss the differential diagnosis of heavily pigmented epithelioid melanocytic neoplasms, and propose a new nomenclature for such tumors.

Uncommon Histopathological Variants of Malignant Melanoma: Part 1

Despite new horizons opened by recent advances in molecular pathology, histological evaluation still remains the diagnostic gold standard regarding cutaneous melanocytic neoplasms. Several histological variants of melanoma have been described, and their knowledge is crucial for accurate diagnosis and classification of cases with unusual clinicopathological features. Uncommon histological variants of melanoma have been described based on a broad constellation of features, including architectural pattern, stromal alterations, cytological attributes, and other morphological properties. This review is aimed at providing an extensive discussion of unusual but distinctive histopathological variants of melanoma.

Animal-type melanoma: dog or wolf? A review of the literature and a case report

The human animal type melanoma (ATM) is a rare subtype of melanoma characterised by the proliferation of pigmented dermal epithelioid and spindled melanocytes. However, this variant of melanoma is still lacking a precise nosography definition and classification for the difficulty to be distinguished from other more common melanocytic lesions, as well as for its peculiar biological behaviour. On the other hand, the contribution of scientific literature to this issue is fragmented and limited to the description of very few cases. Starting from the presentation of a case with abnormally aggressive clinical features, here we revisit the current knowledge on ATM from its dermatologic patterns, epidemiology, demography and histopathology to the clinical management. Peculiar accuracy has also been reserved to several histopathologic criteria, which are critical for the differential diagnosis from other melanocytic diseases in junction with molecular data deriving from recent cytogenetic and mutational characterisation of this tumour.

PD-1 inhibition in congenital pigment synthesizing metastatic melanoma

A newborn female child was born with a congenital pigment synthesizing melanoma of the scalp. Further workup revealed metastatic disease within the liver, lungs, and left tibia. Whole exome sequencing was performed on multiple samples that revealed one somatic mutation, lysine methyltransferase 2C (KMT2C), at low allelic frequency but no v-Raf murine sarcoma viral oncogene homolog B (BRAF), NF-1 mutation. Programmed death ligand 1 was moderately expressed. Treatment was initiated with the programmed cell death protein 1 inhibitor nivolumab. The patient tolerated this treatment well with minimal toxicity. She is now over a year out from initial diagnosis, continuing on nivolumab, with stable disease.

Pigmented Epithelioid Melanocytoma (PEM)/Animal Type Melanoma (ATM): Quest for an Origin. Report of One Unusual Case Indicating Follicular Origin and Another Arising in an Intradermal Nevus

Pigmented epithelioid melanocytoma (PEM) is a tumor encompassing epithelioid blue nevus of Carney complex (EBN of CNC) and was previously termed animal-type melanoma. Histologically PEMs are heavily pigmented spindled and epithelioid dermal melanocytic tumors with infiltrative borders, however, their origin remains unclear. Stem cells for the epidermis and hair follicle are located in the bulge area of the hair follicle with the potential to differentiate into multiple lineages. Multiple cutaneous carcinomas, including follicular cutaneous squamous cell carcinoma (FSCC), are thought to arise from stem cells in the follicular bulge. We present two cases of PEM/ATM in a 63 year-old male on the scalp with follicular origin and a 72 year-old female on the upper back arising in an intradermal nevus. Biopsy of both cases revealed a proliferation of heavily pigmented dermal nests of melanocytes with atypia. The Case 1 tumor was in continuation with the outer root sheath of the hair follicle in the bulge region. Case 2 arose in an intradermal melanocytic nevus. Rare mitotic figures, including atypical mitotic figures, were identified in both cases. We present two cases of PEM, with histologic evidence suggesting two origins: one from the follicular bulb and one from an intradermal nevus.

Pigment-Synthesizing Melanocytic Neoplasm With Protein Kinase C Alpha (PRKCA) Fusion

IMPORTANCE

Melanocytic neoplasms with prominent pigment synthesis mimicking equine melanoma represent a rare variant of biologically indeterminate or low-grade malignant melanocytic tumors in which the molecular profile and exact histologic classification are not established. Tumors with these characteristics rarely occur as congenital lesions. We performed genomic analysis of a congenital pigment synthesizing melanocytic neoplasm with indeterminate biological potential.

OBSERVATIONS

The patient was a 5-month-old girl presenting with a 6-cm protuberant scalp mass, which had doubled in size since birth. Histologic examination showed heavily pigmented intradermal proliferation of large, epithelioid melanocytes with mild cytologic atypia, low mitotic activity, focal necrosis, and ulceration. RNA sequencing identified a novel ATPase, Ca2+ transporting, plasma membrane 4(ATP2B4)-protein kinase C-alpha (PRKCA) fusion transcript. The fusion resulted in an in-frame linkage of the PRKCA catalytic domain with the N-terminal of ATP2B4 and high expression of the PRKCA kinase domain. Break-apart fluorescence in situ hybridization showed PRKCA rearrangement, and reverse transcriptase-polymerase chain reaction confirmed the presence of the fusion transcript. The patient was alive and well, with no evidence of recurrence, at the 1-year follow-up.

CONCLUSIONS AND RELEVANCE

To our knowledge, this is the first report of PRKCA fusions in melanocytic neoplasms. Future studies need to determine the frequency of PRKCA fusions in pigment-synthesizing melanocytic neoplasms.

[Histological spectrum of malignant melanoma]

The diagnosis of melanocytic tumors is one of the most problematic areas in dermatology and diagnostic pathology. Melanoma is a malignant melanocytic tumor and the risk for metastasis and associated mortality is mainly dependent on tumor thickness and depth of invasion. Early recognition and correct diagnosis is therefore important for successful and effective treatment. The correct diagnosis of melanoma is, however, challenging due to the wide morphological spectrum. Historically, the disease was subdivided into superficial spreading, nodular, lentigo maligna and acral lentiginous melanoma but many more subtypes have subsequently been added. Some of these melanoma variants also show differences relating to the genetic background, clinical presentation, prognosis and treatment and may be associated with a specific differential diagnosis. In this article four of these melanoma variants, desmoplastic melanoma, nevoid melanoma, malignant blue nevus and pigment synthesizing melanoma will be discussed in more detail.

Prognostic factors of oral mucosal melanoma: histopathological analysis in a retrospective cohort of 82 cases

AIMS

To investigate the histopathological predictors of overall survival and metastatic failure of oral mucosal melanoma (OMM), of which the histopathological classification and microstaging has not been established.

METHODS AND RESULTS

The pathological data, including cell type (CT), level of invasion, ulceration, mitotic rate, pigmentation, necrosis, tumour-infiltrating lymphocyte (TIL) and vascular invasion, of 82 OMM patients from April 2002 to April 2012 were reviewed and analysed retrospectively. CT, ulceration, mitotic rate, pigmentation, necrosis and vascular invasion were found to be of significance in predicting the overall survival of OMM patients. CT was an independent prognostic factor of overall survival in multivariate analysis. In patients with localized OMM, CT, level of invasion, mitotic rate, pigmentation and necrosis were associated with overall survival but none of them proved to be an independent prognostic factor. CT, mitotic rate and TIL were associated with the risk of distant metastasis. TIL was revealed to be an independent factor of distant metastases risk in multivariate analysis.

CONCLUSIONS

CT was an independent prognostic factor of overall survival. Patients with epithelioid cell type OMM had a poor prognosis. Patients without TIL had a higher risk of distant metastasis.

Animal-type malignant melanoma associated with nevus of Ota in the orbit of a Japanese woman: a case report

We present a patient with an animal-type malignant melanoma associated with the nevus of Ota in the orbit who showed a good prognosis after a combination of orbital extirpation, chemotherapy, stereotactic radiotherapy, and gamma knife. A 42-year-old Japanese woman presented with two tumors, one pathologically diagnosed as right-sided intraconal animal-type malignant melanoma and the other intracranially, presumed to be of the same pathogenesis and both were considered to have arisen from the nevus of Ota. She underwent an extirpation of the orbit, chemotherapy (DAV therapy, which is a combination of dacarbazine, nimustine, and vincristine), stereotactic radiotherapy (54 Gy in 27 fractions), and gamma knife (marginal dose was 17 Gy, target volume was 0.2 ml). She has been alive for 33 months since the extirpation, with no sign of local recurrence, new metastasis, nor enlargement of the intracranial tumor. Not just combination therapy but also the low malignancy of animal-type melanoma may have contributed toward the good prognosis.

Animal-type melanoma: report of five cases with sentinel node biopsy and fluorescence in-situ hybridization analysis

Animal-type melanoma (ATM) is a rare tumor, characterized histologically by a predominantly dermal proliferation of heavily pigmented epithelioid and spindle dendritic melanocytes. Five patients with ATM, who had undergone sentinel node biopsy, were studied: three male and two female, between 4 and 62 years of age (mean, 28.0). Lesion size ranged from 4 to 18 mm and thickness from 0.7 to 5.1 mm. Nodal deposits were found in three patients. Of the patients with positive sentinel nodes, the first showed a minimal nodal involvement in one node, the second multiple deposits in one node, and the third multiple deposits in one sentinel node and a single deposit in another; this last patient also had additional tumor deposits in a nonsentinel regional node. Fluorescence in-situ hybridization tumor analysis proved negative in all cases. All patients are alive and free of disease at 36-95-month follow-up (mean, 53 months). Results showed ATM as a neoplasm characterized by a somewhat high rate of lymph node involvement but relatively low rate of visceral metastases and mortality, appearing as a low-grade malignant tumor.

Age as a predictor of sentinel node metastasis among patients with localized melanoma: an inverse correlation of melanoma mortality and incidence of sentinel node metastasis among young and old patients

PURPOSE

We have previously reported that older patients with clinical stage I and II primary cutaneous. Melanoma had lower survival rates compared to younger patients. We postulated that the incidence of nodal metastasis would therefore be higher among older melanoma patients.

METHODS

The expanded American Joint Committee on Cancer melanoma staging database contains a cohort of 7,756 melanoma patients who presented without clinical evidence of regional lymph node or distant metastasis and who underwent a sentinel node biopsy procedure as a component of their staging assessment.

RESULTS

Although older patients had primary melanoma features associated with more aggressive biology, we paradoxically observed a significant decrease in the incidence of sentinel node metastasis as patient age increased. Overall, the highest incidence of sentinel node metastasis was 25.8 % in patients under 20 years of age, compared to 15.5 % in patients 80 years and older (p < 0.001). In contrast, 5-year mortality rates for clinical stage II patients ranged from a low of 20 % for those 20-40 years of age up to 38 % for those over 70 years of age. Patient age was an independent predictor of sentinel node metastasis in a multifactorial analysis (p < 0.001).

CONCLUSIONS

Patients with clinical stage I and II melanoma under 20 years of age had a higher incidence of sentinel lymph node metastasis but, paradoxically, a more favorable survival outcome compared to all other age groups. In contrast, patients >70 years had the most aggressive primary melanoma features and a higher mortality rate compared to all other age groups but a lower incidence of sentinel lymph node metastasis.

Melolabial fold interpolated flap for reconstruction of complex nasal defects

Complex surgical nasal defects are often technically difficult. We report the case of a 71-year old male diagnosed with a malignant melanoma (animal type; Breslow 1.5; Clark IV) on the right nasal ala. Radial excision with margins of approximately 1.5 cm was performed, creating a complex full-thickness surgical defect involving the free wall and margin of the right nasal ala, the right soft triangle, nasal lobe and columella, which was reconstructed using a melolabial interpolated flap, with highly satisfactory final esthetic result. Interpolated flaps are viable surgical options for the reconstruction of surgical defects for which local flaps and skin grafts are not suitable.

Animal-type melanoma: clinical and dermoscopic features of 3 cases

Animal-type melanoma is a rare variant of malignant melanoma in humans. Although many patients develop locoregional and distant metastases, mortality is lower than in other types of melanoma. We present 3 cases of animal-type melanoma in elderly men and include a description of common clinical and dermoscopic features (homogeneous blue pattern, irregular whitish structures, and irregular large vessels).

RACK1, a clue to the diagnosis of cutaneous melanomas in horses

Background

Melanocytic proliferations are common in horses but the diagnosis of malignancy is not always straightforward. To improve diagnosis and prognosis, markers of malignancy are needed. Receptor for activated C kinase 1 (RACK1) protein may be such a marker. RACK1 was originally found to characterize malignant melanocytic lesions in the Melanoblastoma-bearing Libechov minipig (MeLiM) and, later, in human patients. Our purpose was to investigate the value of RACK1 in the classification of cutaneous melanocytic proliferations in horses.

Results

Using immunofluorescence, we report here that both MITF (Microphthalmia-associated transcription factor) and PAX3 (Paired box 3) allow the identification of melanocytic cells in horse skin samples. Importantly, RACK1 was detected in melanocytic lesions but not in healthy skin melanocytes. Finally, we found that RACK1 labeling can be used in horses to distinguish benign melanocytic tumors from melanomas. Indeed, RACK1 labeling appeared more informative to assess malignancy than individual histomorphological features.

Conclusions

This study confirms that horses provide an interesting model for melanoma genesis studies. It establishes MITF and PAX3 as markers of horse melanocytic cells. RACK1 emerges as an important marker of malignancy which may contribute to progress in the diagnosis of melanomas in both human and veterinary medicine.

The pathology of melanoma

Although melanoma represents only 10% of all skin cancer diagnoses, it accounts for at least 65% of all skin cancer-related deaths. The number of new cutaneous melanoma cases projected during 2010 was 68,000-a 23% increase from the 2004 prediction of 55,100 cases. In 2015, the lifetime risk of developing melanoma is estimated to increase to 1 in 50. As the incidence of melanoma continues to rise, now more than ever, clinicians and histopathologists must have familiarity with the various clinical and pathologic features of cutaneous melanoma.

Animal type melanoma: an unusual case with aggressive histological features?

Animal-type melanoma (ATM) refers to a well-known but rare, heavily pigmented melanocytic tumor, considered a variant of malignant melanoma, the biological behavior and prognostic significance of which still remain to be completely established. We report a case characterized by proliferation of hyperpigmented epithelioid and spindle cells, focally ulcerating the epidermis. Tumor necrosis, perineural and vascular invasion, as well as a slightly high mitotic index, were also observed. Although there were several features indicating poor prognosis, the lesion was diagnosed as ATM and not as classical melanoma. This almost unique case could help us to confirm the excellent biological behavior of this "uncertain malignant potential tumor", suggesting a biological nature of ATM possibly different from classical melanoma, as reported in other molecular studies. In addition, the first rapid impression of aggressive melanoma could lead the pathologist to render an immediate, incorrect diagnosis.

Animal-type melanoma - tumor cell invasion of dermal lymphatics and molecular identification of lymph node metastasis

Animal-type melanoma (ATM) represents a rare subtype within the wide spectrum of melanocytic tumors. Clinically, ATM lesions appear as sharply demarcated, brown, black and dark blue pigmented nodules, which show grey-white surface elements on dermatoscopy. The tumor is restricted to the dermis and arranged in irregular fascicles, which are composed of spindle-shaped and epithelioid melanocytes. Moderate tumor cell pleomorphism, mitoses and apoptotic cells all suggest a malignant process. Abundant, finely dispersed melanin pigment within tumor cells as well as numerous melanophages are strongly suggestive of ATM. Even though locoregional lymph node metastases are frequently found at diagnosis, the course of ATM is generally benign. Specific molecular changes may be detected in melanocytes from lesions and lymph nodes on fluorescence in situ hybridization (FISH). Such findings strongly indicate the malignant potential of ATM. The peculiar biology of ATM, as a moderately malignant tumor, is reflected in a new histopathological classification within the spectrum of dermal borderline melanocytic tumors (BMT).

Pigmented epithelioid melanocytoid tumor of the ocular adnexa

An 8-year-old girl with a history of microphthalmia in the right eye presented with a left medial upper eyelid mass with a dark blue-green nodule that could be seen through the skin but did not appear to involve the overlying epidermis. A biopsy demonstrated a pigmented epithelioid melanocytoid tumor with rare mitoses arising in association with a congenital nevus and positive margins. Due to the pathological findings, the patient underwent excision of the tumor with 5-mm margins and a sentinel lymph node biopsy. The re-excision of the upper eyelid margins demonstrated residual benign congenital melanocytic nevus, but did not reveal residual melanocytic lesion. The parotid sentinel node biopsy revealed benign and cytologically mature nevus nests in the capsule and septa, but there was no evidence of involvement with the pigmented epithelioid melanocytoid tumor. The patient underwent successful eyelid reconstruction and had no evidence of recurrence or metastasis after 2 years.

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.

Blue nevi and related lesions: a review highlighting atypical and newly described variants, distinguishing features and diagnostic pitfalls

Blue nevi and related entities are a heterogenous group of congenital and acquired melanocytic tumors that includes established entities such as dendritic ("common") blue nevus and cellular blue nevus, and their numerous clinical and pathologic variants, such as deep penetrating nevus. They share several clinical and morphologic features including their blue tinctorial properties, the presence of a dermal proliferation of spindle, fusiform or ovoid cells, associated melanin pigment (both within the melanocytic tumor cells and also within macrophages) and stromal sclerosis and, at least focal positivity for HMB-45 (Gp100). Some variants, such as deep penetrating nevus, often show considerable variation in nuclear size and shape, and, as a consequence, are at risk of being misdiagnosed as melanoma by those unfamiliar with their characteristic morphologic features. The so-called malignant blue nevus is a controversial term denoting melanomas arising in association with or exhibiting some morphologic similarities to blue nevus. There are also lesions that are probably related to blue nevi, such as the recently described pigmented epithelioid melanocytoma and the neurocristic hamartomas, whose nature, biologic behavior, and relationship to the better established entities remains to be clearly established. This review aims to present a brief overview of these lesions, highlighting their pathologic characteristics, distinguishing features and potential diagnostic pitfalls, with particular emphasis on recently described entities, molecular findings, controversial areas, and approaches to diagnosis.

Carcinoid-like pattern in melanoma: report of 4 cases

Cutaneous melanoma can produce a wide variety of unusual morphological appearances, sometimes mimicking other tumors. We report on 4 cases of melanoma with carcinoid-like features, namely, arrangement of neoplastic cells in trabecules, ribbons, pseudorosettes, rosettes, and/or small round islands. A total of 10 biopsies from 4 patients were available for a histopathological study comprising congenital nevus, a nodule that had developed in this nevus and its persistence/recurrence, 3 primary cutaneous lesions, 3 metastases, and a recurrent/persistent lesion. In 7 of these 10 lesions, the most characteristic finding was a distinctive arrangement of the neoplastic cells as trabecules, ribbons, pseudorosettes, rosettes, or small round insular islands, thus closely resembling cell arrangement in carcinoids of various organs. All these tumors were positive for melanocytic markers. No neuroendocrine differentiation was demonstrated immunohistochemically. We conclude that the carcinoid-like pattern in melanoma, namely, the pattern in which neoplastic cells are arranged in trabecules, ribbons, cords, rosettes, pseudorosettes, and small round insular nests resembling those in carcinoids, is a distinctive pattern, which may rarely occur in primary cutaneous melanoma, its recurrence or metastasis, or in a melanoma associated with a large congenital nevus. This morphological type of melanoma may produce a serious diagnostic pitfall, but despite a confusing microscopic appearance, these tumors seem to demonstrate a conventional immunohistochemical profile.

Animal-type melanoma: a clinical and histopathological study of 22 cases from a single institution

Background Animal-type melanoma is a rare distinct melanoma subtype, characterized by proliferation of heavily pigmented epithelioid and spindled melanocytes that resembles the heavily pigmented melanomas seen in grey horses. While animal-type melanoma is generally considered to be more indolent than conventional melanoma, only a limited number of cases have been reported and, as such, the clinical characteristics of animal-type melanoma are incompletely understood. Objectives To characterize the clinical and histopathological features of animal-type melanoma, and determine any features that may predict outcome. Patients/Methods Data was extracted from a prospectively collected melanoma database (1994-2008), and a retrospective pathology database (1991-2008) for all patients with a diagnosis of both equivocal (8) and unequivocal (14) malignant animal-type melanoma. We reviewed the clinical and histopathological features, including the sentinel lymph node biopsy (SLNB) status. Results A total of 22 patients were identified, with a median age of 35 years. The median Breslow depth was 2.22 mm. A SLNB was performed in 17 patients, eight (47%) were positive. Younger age was associated with: (i) animal-type melanoma with features equivocal for malignancy (median age of 7 vs. 48 years, P = 0.01), and (ii) a negative SLNB (median age 12 vs. 53 years, P = 0.03). Four patients with unequivocal animal-type melanoma developed recurrent metastatic disease, with one patient death. No patient with an equivocal animal-type melanoma or negative SLNB developed recurrent disease; however, this did not reach statistical significance (P = 0.13 and P = 0.09, respectively). Conclusions Animal-type melanoma has a propensity for regional lymphatic metastasis and is rarely capable of disseminated metastatic disease and death. Animal-type melanoma appears to exhibit a spectrum of biological behaviour, with young patient age associated with more indolent disease.

Oral mucosal melanoma with unusual clinicopathologic features

Oral mucosal melanoma (OMM) is an extremely rare malignancy, accounting for < 0.5% of all melanomas and all oral malignancies. The rarity of OMM, the heterogeneity in clinical and histopathologic appearances, and the paucity of molecular and genetic studies to date have limited our knowledge of the etiopathogenesis of these cancers. A 39-year-old Hispanic male presented for evaluation of a large, pigmented, plaque-like and nodular growth of the maxillary gingival and palatal mucosa. On presentation, a presumptive clinical diagnosis of mucosal melanoma was made, which was confirmed by incisional biopsy with subsequent histopathologic evaluation. Macroscopically, the morphology and highly pigmented nature of the tumor was suggestive of a rarer subtype of melanoma known as animal-type melanoma, also referred to as pigmented epithelioid melanocytoma. However, microscopically, the tumor showed histopathologic features consistent with a high-grade acral (mucosal) lentiginous melanoma with overt cytomorphologic features of malignancy in addition to showing prominent pigment synthesis resembling animal-type melanoma. A detailed search of the literature did not identify a previous report of OMM with prominent pigment synthesis resembling animal-type melanoma. Identification of melanoma subtypes has specific implications for therapeutic approach, and thus their recognition is important to successful patient management.

[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.

Ungewöhnliche Formvarianten maligner melanozytärer Tumoren

Benign and malignant melanocytic neoplasms are relatively frequent and show a broad morphological heterogeneity. The spectrum of malignant melanomas comprises the four main types, superficial spreading malignant melanoma, nodular malignant melanoma, lentigo-maligna melanoma and acrolentiginous malignant melanoma. In addition the rare spitzoid malignant melanoma, desmoplastic malignant melanoma as well as some unusual variants of malignant melanoma can be distinguished. The latter include nevoid malignant melanoma, a form of malignant melanoma resembling benign melanocytic nevi, animal type malignant melanoma, an atypical melanocytic neoplasm with numerous melanophages and prominent melanosis resembling an atypical epithelioid blue naevus as well as regressive malignant melanoma, and representing a questionably distinct entity, balloon cell and signet-ring malignant melanomas, melanoma types with degenerative clear cell changes, as well as myxoid and osteogenic malignant melanomas that are characterized by unusual stromal changes.

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.

Animal-Type Melanoma: A Rare Type of Malignant Melanoma with an Indolent Clinical Behaviour

Animal-type melanoma is an exceedingly rare histological variant of melanoma in humans. The name was coined to reflect similar histological features to melanomas in grey horses. We present a case of animal-type melanoma. The neoplastic cells were heavily pigmented with an epithelioid morphology, round nuclei and prominent eosinophilic nucleoli. Only occasional mitotic figures were identified. The tumour cells had diffuse and nodular growth patterns with involvement of the dermis and the subcutaneous tissue. The patient had a “benign cellular blue naevus” excised 9 years earlier from the same site. Review of the previous case revealed heavily pigmented epithelioid cells with similar morphology to the current case. Nuclear pleomorphism was minimal and only a single mitotic figure was present. The lesion extended to the margins of excision. The diagnosis of animal-type melanoma was made on the current case and on the previously misdiagnosed case.

Recurrence of this case nine years following incomplete excision further supports the hypothesis that animal-type melanoma is a distinct histological type of malignant melanoma with an indolent clinical course.