PRIMARY CUTANEOUS NEUROENDOCRINE CARCINOMA (MERKEL CELL CARCINOMA) CASE REPORTS AND REVIEW OF THE LITERATURE

Merkel cell carcinoma originates from reticular dermis and invades subcutaneous tissues and rarely papillary dermis and dermis. Vascular and lymphatic permeation are commonly seen. Three histological variants of Merkel cell carcinoma have been defined; Trabecular, solid and diffuse. Solid variant is the most common one and diffuse variant has the worst prognosis. The most important prognostic factor has been reported to be initial stage of the disease. Almost half of the lesions are located in the head and neck region although they may be seen in other regions. Based on literature data, it appears that surgical excision alone is not sufficient in the management of these tumors. Local recurrences are common and median time to recurrence is 5-6 months. Although adjuvant therapies, such as radiation and/or chemotherapy, are thought to be beneficial in these cases, it is not clear yet how to integrate these modalities into the management. Durable local control has been achieved in our cases who had radiation therapy subclinical and residual disease. As seen in our cases, distant metastasis is common in Merkel cell carcinoma. Chemotherapy regimens effective in small cell lung cancer have been used although the role of chemotherapy has not been clear yet. In conclusion, post-operative radiation therapy may increase loco-regional control rates in Merkel cell carcinoma. Since distant metastasis is common, adjuvant chemotherapy may contribute to disease-free and overall survival.