[Merkel cell carcinoma].

Merkel cell carcinoma (MCC) is a malignant cutaneous neuroendocrine tumor which may be difficult to diagnose. It mostly occurs in old patients and the commonest sites are the skin of the head and neck and the extremities. MCC appears as a solitary violaceous dome-shaped nodule or indurated plaque. Histopathologic diagnosis may be difficult and three main patterns have been described. With immunohistochemistry studies, MCC express both epithelial (cytokeratins, EMA) and neuroendocrine (NSE, chromogranin, ...) markers. The tumor develops an aggressive course not unlike an aggressive melanoma. Local recurrence and regional lymph node metastases occur in 40 to 75% of cases. Long-term prognosis is unfavorable (3-year survival rate is 55%). Wide surgical excision associated with radiotherapy is the treatment of choice, regional lymph node metastases should be treated by lymph node excision and radiotherapy; chemotherapy should be used in systemic disease.