Skin tumor - Nonmelanocytic - Merkel cell carcinoma

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Skin - Nonmelanocytic tumors

Carcinoma (non-adnexal)

Merkel cell carcinoma

Reviewer: Christopher Hale, M.D. (see Reviewers page)
Revised: 15 July 2012, last major update June 2012
Copyright: (c) 2001-2012, PathologyOutlines.com, Inc.

General
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● Also called neuroendocrine carcinoma of skin
● Originally called trabecular carcinoma

Clinical features
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● Usually adults or elderly
● 60% women
● Face and extremities
● May be associated with squamous cell carcinoma (in situ or invasive), basal cell carcinoma, eccrine duct-like structures
● Aggressive
● Regional nodal metastases are common
● Distant metastases to liver, lung, bones; also testis or other unusual sites
● Rarely appears to arise initially in lymph node, probably due to regression of primary skin tumor
● May derive from Merkel cell in epidermis, derived from neural crest, important for tactile sensation in lower animals

Treatment
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● Wide local resection, regional lymph node resection
● Radiation therapy and chemotherapy as needed

Case reports
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● 83 year old woman with left cheek lesion (Case Report Med 2010;2010:905414)

Clinical images
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Hip lesion

Gross description
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● Nodular or ulcerated red-violet lesion

Gross images
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Hip lesion

Micro description
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● Dermal or subcutaneous centered tumor with monotonous round tumor cells and diffuse infiltration of subcutis
● May have focal trabecular pattern
● Cells have scant eosinophilic cytoplasmic rim, round and vesicular nuclei with finely granular and dusty chromatin and multiple nucleoli
● Also apoptotic nuclei and frequent mitotic figures
● May have vascular stroma with plump endothelial cells
● Epidermis is usually spared
● Rarely has leiomyosarcoma or atypical fibroxanthoma-like areas

Micro images
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Various images

Cytology images
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FNA by anonymous contributor (was CK20+ with perinuclear dot like staining, CD45-, TTF-; flow was CD56+, CD45-)

Positive stains
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● Low molecular weight keratin, CK20 (perinuclear dot like staining), EMA, neurofilament, neuron-specific enolase, CD56 (J Cutan Pathol 2005;32:541)
● Variable chromogranin, synaptophysin and CD117

Negative stains
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● TTF1, CD45/LCA

Electron microscopy
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● Dense core neurosecretory granules and tightly packed intermediate filaments
● Well developed desmosomes

Molecular
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● Abnormalities in #1, #11, #12
● 1p35-36 deletion

Differential diagnosis
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● Lymphoma
● Metastatic small cell carcinoma of lung
● Basal cell carcinoma

End of Skin - Nonmelanocytic tumors > Carcinoma (non-adnexal) > Merkel cell carcinoma

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