Metastatic small cell melanoma to the stomach mimicking primary gastric lymphoma

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.

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.

Malignant Melanoma Metastatic to Gastrointestinal Tract

Malignant melanomas metastatic to the gastrointestinal (GI) tract show a wide range of histologic features, many of which can mimic primary GI malignancies. In this study, we evaluated the clinicopathologic features of 41 cases of malignant melanoma involving the GI tract. Thirty-two patients were men and nine were women; the average patient age was 51.7 years (range, 26-74 years). Twenty-eight patients had a history of malignant melanoma. Thirteen patients, however, did not have a prior history of malignant melanoma; on the basis of the clinical presentation and the behav ior of the GI lesions of these cases, they were presumed to be metastases from regressed or clinically undetected melanomas. The small intestine was the most common site. 12 patients had involvement of multiple GI sites. Clinical diagnoses at presentation included GI bleeding of unknown etiology, small bowel obstruction, rectal carcinoma, gastric ulcer, lymphoma, and cholelithiasis. The three major histologic patterns that mimicked primary GI neoplasms were carcinoma-like, carcinoid-like, and stromal sarcoma-like. The average survival times were 61.9 months after the diagnosis of primary melanoma and 14.4 months from the time of GI tract involvement. Site of malignant melanoma in the GI tract, histologic pattern, and history of a primary lesion outside GI tract did not show any prognostic significance. Although metastatic malig nant melanomas of the GI tract are rare, they should be considered in the differential diagnosis of primary GI tumors. Int J Surg Pathol 2(1):3-10, 1994

Metastatic small cell malignant melanoma: a case requiring immunoelectronmicroscopy for the demonstration of lattice-deficient melanosomes

A case of metastatic malignant melanoma exhibiting small cell morphology is described. The patient had had a previous primary nodular small cell melanoma. The metastatic tumor was examined by conventional histology, light microscope immunohistochemistry, conventional electron microscopy, and ultrastructural immunolabeling. It consisted of small cells, which, however, varied in size and were present in distinct but merging areas. Tumor cells were negative for S-100 protein and very focally positive for cytokeratin: these findings in combination with small cell morphology suggested the possibility of small cell carcinoma. However, other melanocytic markers were positive. Neuroendocrine markers were negative. By electron microscopy, tumor cells lacked unambiguous melanosomes but contained paranuclear aggregates of nondescript granules. Following ultrastructural immunolabeling, these were found to be decorated with gold-labeled HMB-45 antibodies, thereby confirming them as lattice-deficient melanosomes. This tumor is an uncommon example of malignant melanoma where immunoultrastructural analysis helped clarify the nature of otherwise nondescript granules as true but lattice-deficient melanosomes. This is also the first case of small cell melanoma to be studied by electron microscopy.

A study of eleven cutaneous malignant melanomas in adults with small-cell morphology: emphasis on diagnostic difficulties and unusual features

AIMS

To describe the clinicopathological and immunohistochemical features of cutaneous malignant melanomas with a pure or mixed small-cell pattern in 11 adult patients, and to discuss the diagnostic difficulties encountered.

METHODS AND RESULTS

Haematoxylin and eosin-stained sections of each case of cutaneous small-cell malignant melanoma, together with locally recurrent skin lesions and, where available, metastatic deposits, were re-examined. Available immunohistochemical sections were evaluated. Clinical follow-up data were obtained in each case. One patient presented with metastatic disease, the others presented with cutaneous lesions. Suggested initial diagnoses included malignant melanoma, non-Hodgkin's lymphoma, Merkel cell carcinoma and sarcoma. All the tumours were in the vertical growth phase. Nine had a junctional component, often inconspicuous. The lesions showed either a pure small-cell pattern or a mixed pattern with more conventional areas. In one case, there was colonization of a basal cell carcinoma by invasive malignant melanoma. Variable retention of small-cell morphology in local recurrences and metastases was observed, although in some cases more typically pleomorphic cells were present. In the cases tested, there was strong immunostaining for S100 protein and NKI-C3, and variable immunostaining for HMB45 and Melan-A. Non-melanocytic markers were negative.

CONCLUSIONS

The possibility of a small-cell malignant melanoma should be considered in the assessment of cutaneous and non-cutaneous small-cell neoplasms. The correct diagnosis requires careful evaluation for junctional activity, melanin production and the use of a panel of melanocytic markers.

Morphological analysis of nevoid melanoma: a study of 20 cases with a review of the literature

Nevoid melanoma is a rare variant of melanoma characterized by deceptive morphologic features reminiscent of a benign melanocytic nevus. Twenty (13 nodular, 7 verrucous) nevoid melanomas were reviewed with the goal of identifying the predominant architectural patterns, cytologic features, and prognostic indicators. Although at scanning magnification, many lesions showed a strong resemblance to banal compound or dermal nevi, careful inspection in all cases demonstrated subtle pleomorphism and impaired maturation with depth, invariably accompanied by multiple dermal mitoses. Four tumors recurred and three metastasized, with subsequent death of the patients. Follow-up information for a period of at least 3 years was available in eight cases. In this group, mortality was 37.5%, the metastasis rate was 37.5%, and the local recurrence rate was 75%, with an average tumor thickness of 2.5 mm. We conclude that nevoid melanoma may be distinguished from a benign melanocytic nevus by a high index of suspicion, a careful analysis of architecture, and attention to cytologic features. Our data and a review of the literature do not support the notion that nevoid melanoma has a better prognosis than ordinary melanoma.

Small cell malignant melanoma: a variant of naevoid melanoma. Clinicopathological features and histological differential diagnosis

AIMS

To describe the clinical and histopathological features of a rare variant of naevoid melanoma, small cell melanoma, and discuss the histological differential diagnoses.

METHODS

The clinical and histological features of cases of malignant melanoma with the histological features of small (non-Merkel like) melanoma were reviewed and documented. In addition, five cases had available material for immunohistochemistry and this was performed using antibodies to the S100 protein and melan-A, and the HMB-45 antibody.

RESULTS

There were 15 cases of small cell melanoma from 14 (10 female, four male) patients, aged between 30 and 77 (mean, 48.6) years. The trunk was the most common location. In more than half the cases, the provisional diagnosis was melanoma/borderline lesion. All shared similar histological appearances of an intraepidermal component of in situ melanoma and a dermal component of nests of cells with hyperchromatic nuclei and scanty cytoplasm, usually in tightly packed nests. All components (junctional and intradermal) of the lesions investigated by immunohistochemistry were positive both for S100 protein and melan-A. All junctional components were positive with HMB-45, but with variable staining of the dermal components with this antibody.

CONCLUSIONS

Small cell malignant melanoma is postulated to be a distinct histopathological entity and a rare variant of naevoid melanoma. Such lesions can be difficult to interpret and easily missed at scanning magnification because the cells of the dermal component mimic benign naevus cells.

Morphological and immunophenotypic variations in malignant melanoma

A variety of cytomorphological features, architectural patterns and stromal changes may be observed in malignant melanomas. Hence, melanomas may mimic carcinomas, sarcomas, benign stromal tumours, lymphomas, plasmacytomas and germ cell tumours. Melanomas may be composed of large pleomorphic cells, small cells, spindle cells and may contain clear, signet-ring, pseudolipoblastic, rhabdoid, plasmacytoid or balloon cells. Various inclusions and phagocytosed material may be present in their cytoplasm. Nuclei may show bi- or multi-nucleation, lobation, inclusions, grooving and angulation. Architectural variations include fasciculation, whorling, nesting, trabeculation, pseudoglandular/pseudopapillary/pseudofollicular, pseudorosetting and angiocentric patterns. Myxoid or desmoplastic changes and very rarely pseudoangiosarcomatous change, granulomatous inflammation or osteoclastic giant cell response may be seen in the stroma. The stromal blood vessels may exhibit a haemangiopericytomatous pattern, proliferation of glomeruloid blood vessels and perivascular hyalinization. Occasionally, differentiation to nonmelanocytic structures (Schwannian, fibro-/myofibroblastic, osteocartilaginous, smooth muscle, rhabdomyoblastic, ganglionic and ganglioneuroblastic) may be observed. Typically melanomas are S100 protein, NKIC3, HMB-45, Melan-A and tyrosinase positive but some melanomas may exhibit an aberrant immunophenotype and may express cytokeratins, desmin, smooth muscle actin, KP1 (CD68), CEA, EMA and VS38. Very rarely, neurofilament protein and GFAP positivity may be seen.