Other Unusual and Rare Variants of Melanoma

 Composed of enlarged cells with abundant clear to vacuolated-appearing cytoplasm



• Chondroid melanoma
image Malignant epithelioid cells associated with prominent myxochondroid-appearing matrix

• Osteoid melanoma
image Malignant epithelioid cells associated with prominent osteoid-appearing material

• Myxoid melanoma
image Atypical epithelioid cells scattered in prominent myxoid matrix

• Small cell melanoma
image Nests and sheets of small, hyperchromatic-staining cells with scant cytoplasm (high nuclear:cytoplasmic ratio)

• Rhabdoid melanoma
image Proliferation of markedly enlarged and atypical-appearing melanocytes with abundant eosinophilic-staining cytoplasm




Top Differential Diagnoses




• Nevi

• Chondroma or other tumors with cartilaginous differentiation

• Osteoma or other tumors with osseous differentiation

• Benign cutaneous myxoid proliferations

image
Balloon Cell Melanoma
Balloon cell melanoma is composed of nests of large, pale- to clear-staining cells with abundant vacuolated cytoplasm (mimicking sebocytes). Note the associated lymphocytic infiltrate image.


image
Myxoid Melanoma
High magnification of myxoid melanoma shows many single tumor cells and small nests image floating in a prominent mucinous stroma image.

image
Spindle Cell/Pleomorphic Melanoma
This is a case of spindle cell/pleomorphic melanoma, which can mimic spindle cell carcinoma, atypical fibroxanthoma, and pleomorphic sarcoma (as well as other sarcomas). Note the frankly pleomorphic, bizarre-appearing tumor giant cells image.

image
S100 Immunohistochemical Stain in Spindle Cell/Pleomorphic Melanoma
S100 (red chromogen) shows strong and diffuse staining in this case of spindle cell/pleomorphic melanoma, essentially excluding the other tumors in the differential diagnosis.


TERMINOLOGY


Definitions




• Rare variants of melanoma, including clear cell/balloon cell, chondroid, osteoid, myxoid, and rhabdoid melanoma


ETIOLOGY/PATHOGENESIS


Environmental Exposure




• Related to UV exposure in most cases


CLINICAL ISSUES


Epidemiology




• Incidence
image Very rare tumors

• Age
image Typically elderly patients


Site




• Sun-damaged skin, typically head and neck region, upper trunk, forearms


Presentation




• Usually present as papule or nodule with irregular, asymmetric borders


Treatment




• Surgical approaches
image Complete and wide excision, with clinical margins based on Breslow depth


Prognosis




• Depends on typical melanoma prognostic features, such as Breslow depth, ulceration, mitotic count, and presence of perineural or angiolymphatic invasion

• Rhabdoid melanoma reportedly shows aggressive course in most cases


MICROSCOPIC


Histologic Features




• Depends on histologic variant
• Most cases often show areas of conventional-appearing melanoma &/or overlying melanoma in situ

• Clear cell/balloon cell melanoma

image Enlarged cells with abundant clear- to vacuolated-appearing cytoplasm

– May be due to glycogen

image May appear deceptively bland in some cases

• Chondroid melanoma
image Malignant epithelioid cells associated with myxochondroid-appearing matrix

image Often shows areas of overlying melanoma in situ or more conventional melanoma with nesting

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Apr 24, 2017 | Posted by in PATHOLOGY & LABORATORY MEDICINE | Comments Off on Other Unusual and Rare Variants of Melanoma
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