Squamomelanocytic Tumor

 Predominantly composed of atypical squamous cells, with scattered melanocytes

– Melanocytes

image Of low density

image Single, not nested

image Dendritic shaped

image Nuclei not atypical

• Pseudoepitheliomatous hyperplasia associated with malignant melanoma
image Keratinocytes in hyperplastic areas not atypical and connect to epidermal surface

image Mitoses not prominent

image Dyskeratosis absent

• Melanocytic matrixoma
image Dendritic melanocytes intermingled with basaloid epithelial cells with foci of matrical differentiation

• Atypical solid-cystic hidradenoma
image Lacks population of spindled cells with clear cytoplasm and fine melanin pigment

Squamomelanocytic Tumor
Squamomelanocytic tumor is a dermal-based tumor composed of 2 populations of cells: Atypical epithelioid melanocytic cells image and larger squamoid cells image. (Courtesy P. Amerio, MD, PhD.)

Squamomelanocytic Tumor at High Magnification
Squamomelanocytic tumor shows squamoid cells with pink cytoplasm in islands, forming keratin pearls image, surrounded by smaller melanocytic cells image with less distinctive cytoplasm. (Courtesy P. Amerio, MD, PhD.)

Cytokeratin Staining in Squamomelanocytic Tumor
Cytokeratin AE1/AE3 strongly highlights the islands of squamoid cells forming keratin. (Courtesy P. Amerio, MD, PhD.)

Melan-A Staining in Squamomelanocytic Tumor
Melan-A staining is positive in the melanocytic cells surrounding the negative islands of squamoid cells image. (Courtesy P. Amerio, MD, PhD.)



• Admixed histopathologic features of both atypical squamoid and melanocytic cells
image 2 cell types generally within < 1 mm of each other

• Original descriptions were of dermal-based tumors


Field Cancerization Theory

• Common carcinogen (i.e., ultraviolet light) may lead to proliferation of 2 different cell types

Tumor Collision Theory

• By chance, 2 different cell types have mutations and show clonal proliferation

• Arguing against this theory is presence of identical molecular alterations and immunohistochemical staining patterns in both squamous and melanocytic components of some squamomelanocytic tumors

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Apr 24, 2017 | Posted by in PATHOLOGY & LABORATORY MEDICINE | Comments Off on Squamomelanocytic Tumor

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