[Merkel cell carcinoma: a diagnostic and therapeutic challenge].

Merkel cell carcinoma (cutaneous neuroendocrine carcinoma) is a highly malignant, neuroendocrine skin tumor. It mostly occurs in elderly patients in the sun-exposed skin of the head and neck and the extremities. Merkel cell carcinomas develop as fast-growing dermal tumors. They are characterized by a high frequency of lymph-node metastases (50%) and local recurrences (25-77%). The 5-year survival rate is 30-74%. Histology reveals uniform, round cells with a small cytoplasmic rim expressing cytokeratin 20, neurofilament, synaptophysin, chromogranin, and neuron-specific enolase. Ultrastructurally, 100-200 nm electron dense granules are typical findings. Wide surgical excision, followed by radiotherapy, is the treatment of choice. Regional lymph-node metastases should be treated by radical lymph-node excision and radiotherapy. In advanced metastatic Merkel cell carcinoma, a remission can be achieved by different chemotherapy schedules or the somatostatin analogue octreotide. However, the prognosis remains poor. The current knowledge about this disease and guidelines for effective diagnosis and treatment are given.