Unusual variants of malignant melanoma

Abstract

A potential diagnostic pitfall in the histologic assessment of melanoma is the inability to recognize unusual melanoma variants. Of these, the more treacherous examples include the desmoplastic melanoma, the nevoid melanoma, the so-called 'minimal-deviation melanoma,' melanoma with prominent pigment synthesis or 'animal-type melanoma,' and the malignant blue nevus. Also problematic are the unusual phenotypic profiles seen in vertical growth phase melanomas; these include those tumors whose morphological peculiarities mimic cancers of nonmelanocytic lineage and those melanomas that express aberrant antigenic profiles not commonly associated with a melanocytic histogenesis. Metaplastic change in melanoma, balloon cell melanoma, signet-ring cell melanoma, myxoid melanoma, small cell melanoma and rhabdoid melanoma all have the potential to mimic metastatic and primary neoplasms of different lineage derivations. Abnormal immunohistochemical expression of CD 34, cytokeratins, epithelial membrane antigen, and smooth muscle markers as well as the deficient expression of S100 protein and melanocyte lineage-specific markers such as GP100 protein (ie HMB-45 antibody) and A103 (ie Melan-A) also present confusing diagnostic challenges. In this review, we will discuss in some detail certain of these novel clinicopathologic types of melanoma, as well as the abnormal phenotypic expressions seen in vertical growth phase melanoma. Modern Pathology (2006) 19, S41-S70. doi:10.1038/modpathol.3800516Keywords: melanoma; variants; phenotype; immunohistochemistry; morphology Desmoplastic melanoma Introduction and Clinical FeaturesDemoplastic melanoma is a rare variant of malignant melanoma first recognized in 1971.1 Desmoplastic and neurotropic melanoma may be mistaken clinically for a scar, a fibroma, a basal cell carcinoma, or a fibromatosis. Sometimes there is pronounced mucin deposition that imparts a boggy quality to the lesion. 2,3 The clinical clue to the diagnosis, when present, is cutaneous or mucosal pigmentation overlying a palpable dermal or submucosal nodule. That said, only half of desmoplastic melanomas are clinically pigmented. 3 Desmoplastic melanomas tend to occur in the head and neck area and the upper back [4][5][6][7] but are also seen in mucosal sites such as the vulva or gingiva 8 and in acral locations. Typically, they occur in older patients, with mean ages in the larger series falling into the sixth to eighth decades of life. 4,6,[9][10][11][12][13][14][15] Larger series show a male preponderance of 1.75 to 1. 15 Although any given desmoplastic melanoma can be deeply invasive, when matched for depth of invasion, they are associated with a lesser risk of metastatic disease than conventional melanomas of similar depth. The classical clinical finding is that of a pale or fleshy firm nodule reminiscent of a scar, which tends to delay clinical diagnosis and biopsy. Carlson et al,6 who reported an equal distribution in men and women, found most tumors to be located in the head and neck area (75%) and to be nonpigment...

Melanoma arising in association with blue nevus: a clinical and pathologic study of 24 cases and comprehensive review of the literature

“…The criteria to distinguish between melanoma and an associated nevus component included distinctly biphenotypic foci with increased cellularity, prominent nuclear pleomorphism and nucleoli, increased mitotic figures, and the presence of coagulative tumor necrosis. 6 'Tumor thickness' was defined as the standard Breslow thickness when the lesion abutted or came in close proximity to the epidermis or the largest tumor dimension available for a given lesion (when the lesion grew as a nodule at a location distant from the epidermis and/or there was no epidermis available for evaluation in the specimen). Only the malignant component was measured when assessing maximum tumor thickness.…”

“…[3][4][5] Diagnostic histopathologic features include a proliferation of melanocytes with malignant cytology (nuclear pleomorphism, coarse chromatin, prominent nucleoli), increased and/or atypical mitotic figures, tumor necrosis, and invasive and/or destructive pattern of growth and occasionally, an adjacent/associated proliferation of distinctly benign blue nevus dendritic melanocytes. 6 Although melanoma blue nevus type have been shown to exhibit outcomes similar to conventional melanoma when matched for Breslow thickness, age, Clark level, and ulceration, 7 it remains controversial which-if any-of the discrete clinical and pathologic indicators (like age, gender, Breslow thickness, mitotic figures, and ulceration) predictive of clinical outcome in conventional cutaneous melanomas might apply to this group of melanomas. This is especially contentious considering the typical restriction of melanoma blue nevus type to the dermis and/or subcutaneous tissue without an associated intraepidermal component, which has been suggested to undermine the biological relevance of Breslow thickness and tumor ulceration as predictors of outcome.…”

A Rare Case Report of Clear Cell Variant of Oral Squamous Cell Carcinoma

“…Amelanotic melanomas consist of large nests of polygonal, rounded or spindle cells with clear to weakly eosinophilic cytoplasm with positive immunoreactivty S-100 protein and other melanoma-associated antigen such as HMB-45. Present case showed negative staining for S-100 and strong positivity for CK8, and CK18 suggestive of OSCC [7].…”

nbsp; language=pt]Melanoma tipo animal: relato de dois casos

“…O melanoma tipo animal ou equino foi descrito pela primeira vez por Dick, em 1832, em cavalos e compreende a presença de nódulos cutâneos de melanócitos densamente pigmentados (2,6) . Essa neoplasia classicamente se desenvolve em cavalos cinzas e idosos, mas também é descrita em modelos animais não equinos, tais como aqueles induzidos por aplicação tópica cutânea de carcinógenos (6) .…”

“…Essa neoplasia classicamente se desenvolve em cavalos cinzas e idosos, mas também é descrita em modelos animais não equinos, tais como aqueles induzidos por aplicação tópica cutânea de carcinógenos (6) .…”