[Merkel carcinoma]

Merkel's carcinoma is a rare but highly aggressive cutaneous neuroendocrine tumor whose incidence has increased due to an aging population and increased UV exposure. It is characterized by rapid growth, high risk of recurrence and early metastatic spread. Two subtypes have been identified: Merkel polyomavirus-related (MCPyV), present in 80% of cases in Europe, and UV-related. The main risk factors are advanced age, male gender, light phototypes and immunosuppression. Clinically, it appears as a painless, red or purplish nodule, often on photo-exposed areas. Diagnosis is based on histopathology and immunohistochemistry (CK20+ and synaptophysin+). Extension assessment is essential, and relies on PET-CT, brain MRI and lymph node ultrasound. Staging follows the AJCC 8th edition, distinguishing between localized (I/II), lymph node involved (III) and metastatic (IV) stages. Treatment is based on surgery (excision with 1cm margins) and adjuvant radiotherapy. In the case of lymph node involvement, lymph node dissection and radiotherapy are recommended. Metastatic forms now benefit from immunotherapy (anti-PD-1/PD-L1), which has improved prognosis. Merkel carcinoma has a high recurrence rate (25-50%). Monitoring is based on regular clinical and radiological follow-up over several years. Biomarkers such as NSE and anti-MCPyV serology are currently being evaluated.