Abstract
Introduction: Merkel cell carcinoma (MCC) is a rare but aggressive tumor of both epithelial and neuroendocrine origin. MCC presents as a painless, red nodule on sun-exposed parts of the body. The diagnosis is based on characteristic histopathologic features. Methods: A 64-year-old female with a clinical history of multiple non-melanocyte skin cancers and one sebaceous adenoma presented to her primary care with a progressively enlarging cyst on the left thigh for a 4 month duration. Examination revealed a tan-red firm subcutaneous nodule on the left thigh. She was initially treated with a 1-month antibiotic course. Due to her history of multiple carcinomas, duration of the lesion, and no significant improvement with antibiotic therapy, she saw dermatology and a biopsy was performed. The biopsy revealed sheets of small round blue cells with high N:C ratio, finely dispersed chromatin along with abundant mitosis, and crush artifact. The tumor was localized in the dermis with extension into the subcutaneous fat. Immunohistochemical stains were performed including CD3, CD20, CK20, S-100 and NSE. The lesion cells were positive for NSE and CK20 and negative for S-100 which confirmed the diagnosis of Merkle cell carcinoma. Conclusions: Our case is unique because of the location of the tumor, as MCC mostly occurs on sun-exposed areas. Immunosuppression has also been reported as a risk factor for MCC. Wide local excision with adequate margins followed by radiation therapy is the treatment of choice. Though rare, this case highlights that MCC can also present on areas not exposed to the sun.
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