Abstract

Merkel Cell Carcinoma is an aggressive, rapidly growing neuroendocrine tumor. Various reports exist of MCC arising in association with a scar, Bowen’s Disease or other cutaneous growths. Inversely, lymphoepithelioma-like carcinoma of the skin is an indolent neoplasm unlike its counterparts occurring on other anatomical sites – specifically LELC of the nasopharynx which is more common, more aggressive, and more likely to be associated with EBV infection. A 72-year-old male with history of prostate carcinoma was referred for an enlarging nodule on the right forearm present for 3 months and doubling in size over a month. Physical exam noted a 2cm pink-tan, infiltrative nodule resembling a scar. Punch biopsy showed scattered, irregular dermal nests of small blue cells partially obscured by a brisk lymphocytic infiltrate sparing the epidermis. The small blue cells demonstrated nuclear molding, open chromatin pattern and prominent mitotic figures with positive staining of chromogranin, synaptophysin, EMA, CD56, AE1/AE3 and CK20 in a perinuclear dot pattern. TTF-1 and PSA were negative. The diagnosis of MCC histologically mimicking LELC was made following workup to rule out a metastatic neoplasm. MCC typically forms nests of small, round blue cells in the dermis and subcutis, with salt and pepper chromatin and high nuclear to cytoplasmic ratio. Despite this, MCC does exhibit variation in presentation as additional cytologies have been noted outside of the typical neuroendocrine appearance. Termed “combined MCC”, squamous differentiation is most common. IHC is vital in differentiating MCC from histological mimics. LELC consists of a diffuse dermal population of epithelioid cells, heavy lymphocytic infiltrate surrounding and obscuring tumor islands and negative staining for neuroendocrine markers and CK20. We present an atypical clinical and histologic variant of MCC that highlights the importance of identifying unusual presentations of this aggressive neuroendocrine tumor.

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