CASE #2: Merkel cell carcinoma

Also known as trabecular cell carcinoma or cutaneous neuroendocrine carcinoma, Merkel cell carcinoma (MCC) is a malignant neoplasm most likely of neuroectodermal origin. The Merkel cell is a mechanoreceptor that resides in the basal layer of the epidermis. Controversy exists, and MCC may have no relation to Merkel cells. MCC is highly aggressive, so early recognition and therapy are important.

Clinically, MCC presents as a rapidly growing red nodule, usually on the head or neck but sometimes on the extremities or buttocks. The tumor most commonly occurs in patients older than 50 years and shows no gender preference. Approximately one-third of patients have regional lymph-node involvement at presentation. Distant metastases are seen in 40% of patients. The five-year survival rate is 64%.

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MCC is a poorly defined dermal tumor that often infiltrates the subcutaneous fat. The cells are monotonous, small, and round, with a distinctive smudged chromatin pattern. Usually arranged in sheets, cells can also be arranged in nests and trabeculae. Positive perinuclear staining of cytokeratin 20 and cytokeratin CAM 5.2 is characteristic. MCC cells resemble those of other neuroendocrine tumors, such as small cell lung carcinoma, but thyroid transcription factor 1 helps differentiate these two, staining positive in cutaneous metastases from small cell lung carcinoma and negative in MCC.

Stage 1 MCC is defined as localized disease; treatment comprises surgery with wide, 3- to 5-cm local margins, sentinel lymph node biopsy, and radiotherapy. Stage 2 MCC has regional lymph-node metastases and requires surgery, radiotherapy, and chemotherapy. Stage 3 is disseminated disease and should be treated with chemotherapy.

Our patient was sent to a Mohs surgeon for excision.

Dr. Yang is assistant professor of dermatology at Baylor College of Medicine in Houston.