Merkel Cell Carcinoma—Update on Diagnosis, Management and Future Perspectives

SIMPLE SUMMARY: Merkel cell carcinoma (MCC) is a highly aggressive skin cancer and the second cause of skin cancer death after melanoma. MCC is an immunogenic tumor. In recent years, the use of immunotherapy has changed the treatment landscape for patients with metastatic MCC, significantly improving the prognosis. However, the five-year disease-specific survival remains around 64%, underlying the unmet need for novel treatments. This review recapitulates current knowledge about MCC pathogenesis, diagnosis, and management. Emphasis is given to the use of immunotherapy and targeted therapies as well as to future therapeutic perspectives in the neoadjuvant setting and for locally advanced and metastatic MCC. ABSTRACT: MCC is a rare but highly aggressive skin cancer. The identification of the driving role of Merkel cell polyomavirus (MCPyV) and ultraviolet-induced DNA damage in the oncogenesis of MCC allowed a better understanding of its biological behavior. The presence of MCPyV-specific T cells and lymphocytes exhibiting an ‘exhausted’ phenotype in the tumor microenvironment along with the high prevalence of immunosuppression among affected patients are strong indicators of the immunogenic properties of MCC. The use of immunotherapy has revolutionized the management of patients with advanced MCC with anti-PD-1/PD L1 blockade, providing objective responses in as much as 50–70% of cases when used in first-line treatment. However, acquired resistance or contraindication to immune checkpoint inhibitors can be an issue for a non-negligible number of patients and novel therapeutic strategies are warranted. This review will focus on current management guidelines for MCC and future therapeutic perspectives for advanced disease with an emphasis on molecular pathways, targeted therapies, and immune-based strategies. These new therapies alone or in combination with anti-PD-1/PD-L1 inhibitors could enhance immune responses against tumor cells and overcome acquired resistance to immunotherapy.