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

Orbital Pigmented Epithelioid Melanocytoma Tumor Associated With Nevus of Ota (Oculodermal Melanocytosis)

The authors report a patient with nevus of Ota (oculodermal melanocytosis) who presented with pigmented epithelioid melanocytoma in the right orbit. A 36-year-old female patient attended with proptosis OD and diplopia for 3 months. MRI disclosed an expansive lesion adhered to the right inferior rectus muscle, enlargement of the superior orbital fissure, and filling of the right cavernous sinus. Excision of the orbital mass through a transconjunctival inferior fornix access disclosed a heavily pigmented lesion. Anatomopathological study revealed a diagnosis of pigmented epithelioid melanocytoma. A positron emission tomography scan did not show any metastasis. The patient was submitted to radiotherapy, had an improvement of the proptosis and diplopia, and showed no distant metastases for 3 years now. Pigmented epithelioid melanocytoma belongs to the group of heavily pigmented neoplasms, as do atypical blue nevus, which is characterized by prominent melanin production and a low degree of malignancy.

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.

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.

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.

[Bestiaries in clinical dermatology]

Metaphors have always played a role in the medical tradition and in dermatology too. Beyond their initially playful aspect, metaphors offer a way of rapidly identifying a lesion and of linking it to one or more diseases. They also play a role in the education of medical students and residents by making it easier to memorise different diseases. Herein we discuss "animal" metaphors.

[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.

Differential diagnosis of heavily pigmented melanocytic lesions: challenges and diagnostic approach

The differential diagnosis of heavily pigmented melanocytic neoplasms includes melanoma (especially animal type), melanosis of partially or completely regressed melanoma, blue naevus (BN), pigmented Spitzoid lesions, recurrent naevus, combined naevus, pigmented spindle cell naevus, epithelioid blue naevus of the Carney complex/pigmented epithelioid melanocytoma, deep penetrating naevus, hyperpigmented scar after surgery of melanoma in which there are also melanophages and hyperpigmentation due to the minocycline, a tattoo or a hyperpigmented scar. Pathologists face challenges when evaluating a pigmented lesion, especially in a small superficial biopsy, because it is difficult to access important histopathological features to differentiate benign versus malignant melanocytic lesions. The histological features that favour a diagnosis of melanoma include dimension (>6 mm), asymmetry, poor circumscription, irregular confluent nests, confluent lentiginous junctional melanocytic proliferation, lack of maturation with descent in the dermis, suprabasal pagetoid melanocytes, asymmetrical distribution of melanin pigment, cytological atypia, dermal mitotic figures, asymmetrical dermal lymphocytic infiltrate and necrosis.

Cross-species models of human melanoma

Although transformation of melanocytes to melanoma is rare, the rapid growth, systemic spread, as well as the chemoresistance of melanoma present significant challenges for patient care. Here we review animal models of melanoma, including murine, canine, equine, and zebrafish models, and detail the immense contribution these models have made to our knowledge of human melanoma development, and to melanocyte biology. We also highlight the opportunities for cross-species comparative genomic studies of melanoma to identify the key molecular events that drive this complex disease.

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.

Mucosal melanomas in the elderly: challenging cases and review of the literature

Melanomas are malignant tumors that originate from melanocytes. They are most frequently localized in the skin, but 5% of all melanomas interest also extracutaneous sites as mucosal surfaces, parenchymatous organs, the retroperitoneum area, and the ocular ball. The purpose of this study was to investigate the epidemiologic and morphologic data of mucosal melanomas diagnosed at Emergency City Hospital (Timisoara, Romania) during a period of 12 years. The study included 17 cases of extracutaneous, extraocular melanomas, with 16 primary melanomas and one secondary melanoma. All our patients were older than 53 years and were mostly men. Most of the patients presented with localized disease; only one case had regional lymph node metastases, and another one had systemic metastases at the time of diagnosis. Regarding localization, nine of 16 melanomas were in the head and neck region, six were diagnosed in the gastrointestinal and urogenital tracts (three cases each), and one case had a rare localization (retroperitoneum). The most common histologic type was represented by epithelioid cells, and the majority of the tumors were achromic. Mucosal melanoma is a tumor associated with aging, all our patients being older than 53 years. Because of unspecific symptoms and low incidence, the diagnosis is often delayed and requires teamwork among the clinician, pathologist, radiologist, and oncologist. Different genetic fingerprints impose a correct diagnosis to offer the patient the best novel, personalized therapy.

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.

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.

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).