Morphological and immunocytochemical features of Merkel cell carcinoma metastatic to the pancreas diagnosed by endoscopic ultrasound-guided fine-needle aspiration

Merkel cell carcinoma (MCC) is a rare neuroendocrine carcinoma of the skin, originally described by Toker in 1972, showing highly aggressive behavior and frequent local, regional, and distant spread.1 The etiology of MCC is unknown; however, risk factors include increased age, immunosuppression, and radiation exposure.2 More recently, a viral etiology has been considered since a new polyomavirus, i.e. Merkel cell polyomavirus, was isolated from MCC tumor tissues.3 MCC metastases to the pancreas are uncommonly observed and may represent a diagnostic challenge, in particular on cytology specimens, which are frequently the only specimens available from a suspicious pancreatic mass.4, 5 Here we report a case of MCC metastatic to the body and tail of the pancreas, diagnosed by endoscopic ultrasound‐guided fine‐needle aspiration (EUS‐FNA).