A case series and literature review of Merkel cell carcinoma metastasizing to pancreas.

BACKGROUND: Merkel cell carcinoma is a rare aggressive tumor arising from the mechanoreceptors of the epidermis with a relative higher mortality rate stage for stage than melanoma. Microscopically, the cells appear similar to small cell lung cancer, but they specifically stain positive for CK20 and are negative for TTF-1. It is rarely known to metastasize to the pancreas.

AIMS: To report four cases of Merkel cell carcinoma metastasizing to pancreas and compare them to previously reported patients.

METHODS: We performed a retrospective review of all patients who underwent endoscopic ultrasound with fine-needle aspiration (EUS-FNA) for a suspected pancreatic lesion between January 2004 and December 2012. We reviewed other reported cases with a literature search using PubMed, Embase, and Scopus.

RESULTS: Four male patients with mean age of 66 years were found to have metastatic disease in the pancreas on average 29 months after initial diagnosis of MCC. Two cases were diagnosed with EUS-FNA and two with PET-CT. Three patients had multifocal pancreatic involvement which has not been previously described. All four patients died within 3-9 months following tumor spread to the pancreas. Merkel cell carcinoma rarely metastasizes to the pancreas with only 10 cases being described in the medical literature.

CONCLUSIONS: EUS-FNA is an effective tool that can be utilized in diagnosing pancreatic masses. Differentiating metastatic pancreatic tumors, especially Merkel cell carcinoma from primary pancreatic tumor is useful as systemic therapy is an option in pancreatic adenocarcinoma, but is ineffective in metastatic Merkel cell carcinoma.