Merkel‑cell carcinoma (MCC) is a rare, aggressive cutaneous malignancy of neuroendocrine origin. Clinically it usually presents as a rapidly growing, painless, firm nodule on sun‑exposed skin and has a high propensity for local recurrence and regional or distant metastasis. Because of its behavior and histology, MCC requires prompt diagnostic biopsy and multidisciplinary management.
Clinical features and diagnosis
Typical lesions are solitary, dome‑shaped or dome‑to‑flat nodules with smooth, often shiny skin. The head and neck are common sites; other frequently affected areas include the extremities and periorbital skin. Diagnosis is established by skin biopsy and histopathology. Immunohistochemical staining is used to distinguish MCC from other small‑cell neoplasms: a characteristic perinuclear dot pattern with cytokeratin 20 (CK20) and positivity for neuroendocrine markers support the diagnosis. MCC can mimic metastatic small‑cell carcinomas, and additional markers such as thyroid transcription factor‑1 (TTF‑1) help separate MCC from pulmonary small‑cell carcinoma.
Causes and biology
MCC arises through two main biological pathways. A substantial proportion of cases are associated with integration of Merkel cell polyomavirus (MCPyV) into tumor DNA; viral oncogenes drive tumorigenesis in these MCPyV‑positive tumors. Other cases are MCPyV‑negative and instead show extensive ultraviolet (UV)‑induced DNA damage. Both viral status and UV exposure contribute to the molecular landscape of the disease. Immunosuppression—whether from medications, organ transplantation, HIV infection, or advanced age—also increases risk and is linked to more aggressive behavior.
Risk factors and notable associations
- Advanced age and fair skin are common demographic associations.
- Chronic ultraviolet radiation exposure and history of other skin cancers.
- Impaired immune function (iatrogenic immunosuppression, hematologic malignancy, HIV).
- MCPyV infection is found in many tumors and was identified in the 2000s as a key etiologic agent.
Treatment and prognosis
Management of MCC typically combines surgery, nodal evaluation (often sentinel lymph node biopsy), and radiotherapy. For advanced or metastatic disease, systemic therapy has shifted from cytotoxic chemotherapy toward immune checkpoint inhibitors that target the PD‑1/PD‑L1 pathway; these agents have produced more durable responses for many patients. Prognosis depends strongly on stage at diagnosis: localized tumors treated early have better outcomes, while regional nodal involvement or distant metastases carry a higher risk of recurrence and mortality.
History, terminology and public health
The tumor was first characterized in the early 1970s and has been called by several names, including primary neuroendocrine carcinoma of the skin, trabecular carcinoma, and cutaneous APUDoma. Awareness has grown since the discovery of MCPyV, which clarified a viral contribution to pathogenesis in many cases. Although MCC is uncommon—often described as only a few cases per million population—it is important in dermatology and oncology because of its aggressiveness and rising incidence with aging populations. Further reading and clinical guidance are available from specialty resources: clinical overview and information on risks related to immune status can be found at immune‑related resources.