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19 March 2014 - Case #304

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Thanks to Dr. Jerad Gardner, University of Arkansas for Medical Sciences, for contributing this case.


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Case #304

Clinical history:
A 55 year old woman presented with a skin nodule on the chest.

Microscopic images:



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Diagnosis: Merkel cell carcinoma with overlying squamous cell carcinoma in situ

Immunostains:

Chromogranin

Synaptophysin

Cytokeratin

CK20

p63



Discussion:
This is a nice example of a collision between 2 known entities, in situ squamous cell carcinoma / Bowen disease and dermal Merkel cell carcinoma. Squamous cell carcinoma is common and derives from keratinocytes in the epidermal layer, often due to sun (UV light) exposure.

Merkel cell carcinoma appears to derive from Merkel cells, which are specialized skin cells important for proper neural encoding of light touch stimuli. They have recently been shown to arise from skin lineage, not neural crest (Dev Biol 2009;336:76). Merkel cell carcinoma is an aggressive cutaneous neuroendocrine tumor with a rising incidence (Curr Dermatol Rep 2014;3:46). Histologically, it is dermal or subcutaneous centered with monotonous round tumor cells with a scant eosinophilic cytoplasmic rim, round and vesicular nuclei with finely granular and dusty chromatin and multiple nucleoli. There is frequent apoptosis and mitotic figures. The stroma may be vascular, with plump epithelial cells.

Merkel cell carcinoma has a 5 year survival of only 46%, and has metastatic potential regardless of the size of the primary tumor. To date, there is no effective treatment for recurrent or metastatic disease, although detection of polyoma virus in these tumors suggests that alternatives to chemoradiotherapy may be more effective (Science 2008;319:1096).




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