Merkel cell carcinoma: current state of the problem, molecular basis, and therapeutic options

Merkel cell carcinoma (MCC) is a rare but highly aggressive neuroendocrine skin tumor characterized by early metastasis and an unfavorable prognosis. In recent years, our understanding of its etiology has substantially expanded, including the role of Merkel cell polyomavirus (MCPyV), ultraviolet radiation, and immunodeficiency-related conditions. This review summarizes current data on the epidemiology, risk factors, and molecular pathogenesis of MCC (MCPyV-associated and UV-induced pathways), as well as histological and immunohistochemical criteria for diagnosis. The article describes the clinical presentation, staging according to the 8th edition of the AJCC system, and key prognostic factors, including disease stage, immune status, age, and tumor molecular subtype. Particular attention is paid to modern treatment approaches: for locoregionally advanced disease, wide surgical excision and adjuvant radiotherapy form the backbone of local control; in metastatic MCC, immune checkpoint inhibitors (avelumab, pembrolizumab) have demonstrated high objective response rates and improved survival compared with previous chemotherapy regimens. The review concludes that integrating molecular biology, early diagnosis, and personalized immunooncologic strategies is essential for optimizing the management of Merkel cell carcinoma.