Solitary pancreatic metastasis of occult pulmonary small cell carcinoma diagnosed by EUS-FNA cytology: a case report.

A 74-year-old man presented with symptoms suggestive of acute pancreatitis, and a mass lesion measuring 25 mm was detected in the pancreatic head. Cytological and histopathological examinations of EUS-FNA specimens taken from the lesion demonstrated small cell (neuroendocrine) carcinoma. Tumor cells were immunoreactive for cytokeratin, synaptophysin, chromogranin A, CD56, and TTF-1, and PET-CT of the chest revealed a small tumor in the upper lobe of the left lung. Pulmonary carcinoma, particularly small cell carcinoma, infrequently presents with a solitary metastatic lesion in the pancreas as an initial manifestation and clinically simulates a primary pancreatic neoplasm. Because primary small cell carcinoma of the pancreas is very uncommon, metastasis from the lung should always be considered when evaluating pancreatic neoplasms showing a "small cell" morphology. Immunohistochemistry for TTF-1 is useful for determining the pulmonary origin of this type of neoplasm, and its application to cytology specimens is recommended.