Merkel cell carcinoma: outcome and role of radiotherapy

Merkel cell carcinoma (MCC) are rare neuroendocrine malignant tumor of the skin, occurring in elderly patients. It affects primarily the sun-exposed areas of the skin, with approximately 50% of all tumors occurring in the face and neck and 40% in the extremities. Immunohistochemical markers (CK20+, CK7- and TTF1-) are used to distinguish between MCC and other tumors. MCC have a tendency to rapid local progression, frequent spread to regional lymph nodes and distant metastases. Due to the rarity of the disease, the optimal treatment has not been fully defined. Localized stages (stages I and II) are treated by surgical excision of the primary tumor (with 2 to 3 cm margin) and lymphadenectomy in case of node-positive disease, followed by external beam radiotherapy (EBRT) to a total dose of 50 to 60Gy in the tumor bed. Adjuvant EBRT has been shown to decrease markedly locoregional recurrences and to increase survival in recent studies. Treatment of lymph nodes area is more controversial. Chemotherapy is recommended only for metastatic disease.