Metastatic Merkel cell carcinoma with an unknown primary tumor presenting as lymphadenopathy: A case report.

introduction and importanceMerkel cell carcinoma is one of the rare neuroendocrine tumors of the skin. Neuroendocrine nodal MCCUP is a rare and poorly understood malignancy. In this article, we introduce a case of MCCUP with primary manifestation of lymphadenopathy. CASE PRESENTATION: A 62-year-old woman presented with lymphadenopathy in the inguinal region, and the diagnosis of metastatic Merkel cell carcinoma was made in the excisional biopsy. The primary source of the tumor was not found in the imaging workup and the patient underwent lymphadenectomy. CLINICAL DISCUSSION: MCCUP is a rare subtype of MCC, with specific diagnostic criteria. Most MCCs are symptom-free, requiring biopsy for confirmation. NE tumor marker analysis is crucial for distinguishing NE carcinoma, with CK20 and another NE marker sufficient for MCCUP diagnosis. LCA is not found in MCC tumors, and Ki-67 is used for prognosis. Treatment includes surgery, radiotherapy, and sometimes chemotherapy, although its efficacy is debated.

conclusionMCCUP is a rare disease affecting primarily elderly, several treatment regimens have been considered for the treatment of this rare tumor. One of the treatments with good results can be extensive surgery and patient follow-up.