Keywords: MCC; MCC, Merkel cell carcinoma; MCC-KP, MCC with known primary tumor; MCC-UP; MCC-UP, MCC with unknown primary tumor; MCPyV; MCPyV, Merkel cell polyomavirus; MCV; PyV; UV, ultraviolet radiation; cutaneous neuroendocrine carcinoma; cutaneous oncology; immunosuppression; merkel cell carcinoma; merkel cell polyomavirus; metastatic merkel cell carcinoma with unknown primary tumor; neuroendocrine carcinoma; oncology; polyomavirus.