Merkel cell carcinoma: A clinically oriented mini-review for dermatologists

Abstract

Background: Merkel cell carcinoma (MCC) is a rare but highly aggressive cutaneous neuroendocrine malignancy with mortality rates exceeding melanoma at comparable stages. Its incidence is increasing worldwide, particularly among elderly, immunosuppressed, and fairskinned individuals. Clinically, MCC often presents as a rapidly enlarging, asymptomatic nodule on sun-exposed skin, although atypical locations and morphologic variants may delay recognition. Summary: This clinically oriented mini-review summarizes current evidence most relevant to dermatologists regarding the epidemiology, risk factors, clinical presentation, histopathology, immunohistochemical diagnosis, staging, imaging, prognostic factors, circulating biomarkers, and treatment of MCC. Diagnosis relies on histopathology and immunohistochemistry, with cytokeratin 20 and Merkel cell polyomavirus (MCPyV)-related markers playing important roles in distinguishing MCC from other small round blue cell tumors. Imaging modalities, particularly FDG-PET/CT, are essential for accurate staging and surveillance. Prognosis is influenced by tumor size, stage, immune status, age, and viral status. Emerging biomarkers such as circulating tumor DNA and MCPyV oncoprotein antibody titers are increasingly relevant for disease monitoring. Management is stage-specific and multidisciplinary, involving surgical excision, radiotherapy, and immune checkpoint inhibitors such as avelumab, pembrolizumab, nivolumab, and retifanlimab, which have improved outcomes in advanced disease. Key Messages: MCC is an uncommon but highly lethal skin cancer that requires early recognition, accurate staging, and multidisciplinary management. Dermatologists should be aware of both classic and atypical presentations to avoid delayed diagnosis. Recent advances in imaging, biomarkers, and immunotherapy have improved disease monitoring and treatment, but important global disparities remain in access to diagnostic tools and modern therapies.