Pancreatic neuroendocrine tumors with somatostatin expression and paraganglioma-like features

A small fraction of pancreatic neuroendocrine tumors (PanNETs) shows a solid, paraganglioma-like (PG-like) histology. We wanted to know whether these PanNETs have a special hormone expression and are related to paragangliomas (PGs)/pheochromocytomas (PCs). We screened a series of 48 surgically resected PanNETs for their histological growth patterns and their association with expression of islet hormones. The PanNETs were divided into PG-like and non-PG–like tumors and immunohistochemically monitored for the expression of islet hormones, cytokeratins, and S100. The results were correlated to histological pattern, lymph node status, and data in 28 PGs/PCs, including 2 PGs attached to the pancreas. All PanNETs, in contrast to PGs/PCs, were cytokeratin positive. A PG-like growth pattern was identified in 9 of 48 PanNETs and correlated with somatostatin expression. Only half of the non-PG–like PanNETs also contained somatostatin-positive cells. Eight of 28 PGs/PCs expressed somatostatin, mostly in individual cells. PG-like PanNETs and non-PG–like PanNETs infiltrated the adjacent pancreatic tissue, whereas 2 to the pancreas-associated PGs were well demarcated. Lymph node metastases were detected in 58%, 39%, 57%, and 53% of the somatostatin-producing, somatostatin-negative, PG-like, and non-PG–like PanNETs, respectively. PG-like PanNETs, in contrast to PG/PCs, are characterized by the expression of cytokeratin and somatostatin, the development of lymph node metastasis, and the infiltration into pancreatic parenchyma. Non-PG–like PanNETs may also express somatostatin and show lymph node metastases to the same extent. A literature review of cases reported as PG of the pancreas reveals that only a small fraction of these tumors probably represents true pancreatic PGs.