Abstract
A 57-year-old man was evaluated for a chief complaint of right inguinal swelling. Computed tomography (CT) showed a 34×26 mm mass consistent with an enlarged inguinal lymph node. Excisional biopsy of the lymph node was performed, and histopathological examination showed findings of neuroendocrine carcinoma. However, a systemic search including endoscopy and positron emission tomography-CT found no evidence of a primary lesion. Immunohistochemistry (IHC) showed positive results for neuroendocrine tumor markers, including CD56, synaptophysin, and chromogranin A ; negative results for CK7 ; and positive results for CK20. Merkel cell carcinoma was suspected. Further treatment included lymph node irradiation and follow-up observation.
Merkel cell carcinoma is a rare skin tumor most often found in Caucasian males and shows poor prognosis. This patient underwent systemic evaluation for lymph node metastases originally considered to arise from neuroendocrine tumor with an unknown primary site. However, IHC suggested primary Merkel cell carcinoma involving a lymph node as the most likely diagnosis.
