The Great Impostor: A challenging case of small-cell melanoma with isolated adrenal metastasis.

Small-cell melanoma masquerading as an adrenal non-Hodgkin lymphoma. The index report illustrates the deceptive cytomorphologic features of a small cell type malignant melanoma metastatic to the adrenal gland. The diagnosis was confirmed by performing immunocytochemistry on the cell block sections. The key cytomorphologic mimics and their distinctive features have also been highlighted.

Metastatic melanoma and rare melanoma variants: a review.

The histopathological diagnosis of melanoma is fraught with potential pitfalls. In the setting of cutaneous metastatic melanoma, it is important to recognise the various histological patterns that can be encountered from the more common to the rare, including epidermotropic, folliculotropic, naevoid, and blue naevus-like. In addition, melanoma is notorious for phenotypic plasticity. Thus, there are many different subtypes and cytomorphological variations that can be difficult to recognise as melanoma, particularly in the recurrent or metastatic setting. Select melanoma variants including primary dermal, clear cell, plasmacytoid, signet ring cell, small cell, myxoid, rhabdoid, and dedifferentiated melanoma will be discussed, in addition to composite melanocytic neoplasms. This review is intended to remind the practitioner of key concepts of metastatic disease and select rare melanoma variants, while providing practical guidelines for accurate diagnosis.

Cytologic features of small cell melanoma.

Small cell melanoma (SCM) is an aggressive variant of malignant melanoma (MM), which has been rarely described in the cytology literature. The aim of this study was to describe the clinical and cytologic features of a series of cases of metastatic SCM with discussion of the differential diagnosis of metastatic SCM diagnosed by fine-needle aspiration (FNA). A retrospective review of cases was performed, identifying two FNA cases and one core biopsy with touch preparation of metastatic SCM. Clinical presentation, cytomorphology features, ancillary tests, and final diagnoses were documented and analyzed. Patients ranged in age from 69 to 85 years-old. Cytomorphologic features included the presence of a monomorphic population of dispersed small round blue cells, with scant cytoplasm, high nuclear to cytoplasmic ratios, dense nuclear chromatin, and inconspicuous nucleoli. Acinar like arrangement (n = 2) and nuclear molding (n = 1) were also present. All cases showed diffuse positivity for the melanocytic markers SOX10 and Melan A by immunohistochemistry (IHC). Expression of neuroendocrine markers was variable. Diagnosing metastatic SCM at unusual anatomic sites by FNA cytology is a challenging task, especially in patients without known prior history of melanoma. Cytomorphology of SCM is unique, differing from conventional MM in many aspects, including the presence of acinar formations and a lack of typical melanoma features, such as large cells, intracytoplasmic melanin, and macronucleoli. IHC is critical for establishing the diagnosis of SCM.

Malignant melanoma with areas of rhabdomyosarcomatous differentiation arising in a giant congenital nevus with RAF1 gene fusion.

A girl, born with a posterior  lumbosacral giant congenital nevus, developed a central nodule that expanded over a period of 14 months into a 10-cm pedunculated mass. Histological analysis of the mass revealed melanoma of myxoid, small round-cell type with areas of  rhabdomyosarcomatous  transformation confirmed by immunohistochemistry. RNA sequencing identified an in-frame SASS6(e14)-RAF1(e8) fusion in both components and the nevus. A RAF1 FISH break-apart test found a balanced rearrangement pattern in the nevus and an unbalanced pattern in the malignant areas. Wild-type status of NRAS and BRAF was confirmed by NGS techniques. The array-CGH profile displayed copy number alterations commonly found in rhabdomyosarcomas. Despite intensive treatment, widespread metastatic evolution of the melanomatous component was observed.

Small Cell Variant of Metastatic Melanoma: A Mimicker of Lymphoblastic Leukemia/Lymphoma.

It is well-known to pathologists that melanoma is "the great mimicker" and can look like anything. Despite this widespread awareness, the diagnosis remains a continuous challenge, especially when a metastatic melanoma with rare morphology is examined. We report a case of a 64-year-old man with a lung mass and right-sided pleural effusion who underwent video-assisted thoracoscopic surgery for pleural decortication. The history of melanoma was not reported to us. Microscopic examination revealed sheets of small round blue cells infiltrating into the adipose tissue in a lace-like pattern mimicking lymphoblastic lymphoma. Immunohistochemical stains for melanocytic markers, including S-100 protein, Mart-1, and HMB-45, highlighted the neoplastic cells. The tumor was also positive for CD56 and CD117, but negative for pancytokeratin, CD45, cytokeratin 8, TTF-1, WT1, CD34, chromogranin, synaptophysin, and neuron-specific enolase. The findings were most consistent with metastatic small cell melanoma, an uncommon variant of melanoma that closely resembles lymphoblastic lymphoma and other malignant small round blue cell tumors. To our knowledge, we are the first to describe a case of metastatic small cell melanoma to the pleura in an adult. Clinical and histological details are provided with a review of the literature.

New insights into naevoid melanomas: a clinicopathological reassessment.

AIMS: Because the term 'naevoid melanoma' has variable clinical and pathological interpretations, we aimed to clarify the features of melanomas referred to as naevoid. METHODS AND RESULTS: A review was undertaken of 102 melanomas diagnosed histopathologically as naevoid melanomas and ascertained by European Organization for Research and Treatment of Cancer Melanoma Group Subcommittee pathologists from their records. We found these could be classified morphologically into three groups. Thirteen melanomas were overlying genuine naevi and were therefore excluded. Of the 89 melanomas considered to be naevoid, 11 presented clinically as exophytic papillomatous nodules with little junctional component and composed of small atypical cells showing numerous mitoses and no change with depth; we termed these 'papillomatous naevoid' melanomas. The other 78 were flat or only slightly raised, and had a superficial spreading melanoma-like component with maturation to a small cell, but still an atypical, dermal component; we termed these 'maturing naevoid' melanomas. We showed that papillomatous and maturing naevoid melanomas also have differing immunochemical profiles. Preliminary clinical follow-up suggested different outcomes for these two naevoid melanoma types. CONCLUSIONS: Melanomas that have been classified as naevoid melanomas comprise two types with distinct clinical, histopathological and immunohistochemical features that may also be prognostically significant.

Nevoid Melanoma.

This article discusses the key features of nevoid melanoma. Gross features, microscopic features, immunohistochemistry, differential diagnosis, diagnosis, prognosis, and treatment are also discussed.