[Merkel cell carcinoma]

Merkel cell carcinoma is a rare, highly aggressive skin tumor with neuroendocrine features found in older people. The pathogenesis is associated with immunosuppression, chronic UV light exposure and the Merkel cell polyomavirus. Clinically, Merkel cell carcinoma presents as a solitary, cutaneous or subcutaneous, red to bluish node. Due to early lymphogenic metastasis, locoregional metastases are already present in approximately 30% of cases at the time of diagnosis. The frequent local recurrences as well as the regional and distant metastases usually appear within the first 2-3 years after the initial diagnosis. The first treatment after diagnosis consists of complete surgical removal of the primary tumor with wide safety margins as well as a sentinel lymph node biopsy. Subsequently, adjuvant irradiation of the primary site should be performed. By additional radiotherapy of the regional lymph node stations, the rate of locoregional recurrence can be reduced. For systemic therapy of advanced Merkel cell carcinoma checkpoint inhibitors targeted against the PD-1/PD-L1 axis have proven to be highly and durably effective. In contrast the formerly frequently used chemotherapy shows moderate to good response rates but they are as a rule very short-lived.