Histologic Variants : Rhabdoid PanNET
Histologic Variants of Pancreatic Neuroendocrine Tumors: Many histologic variants of pancreatic neuroendocrine tumors (PanNETs) have been described, including oncocytic, pleomorphic, clear cell, pigmented, and rhabdoid. Rhabdoid variant: Rare examples of pancreatic neuroendocrine tumors display rhabdoid morphology. The tumor cells are monotonous and arranged in solid sheets. The nuclei are uniform, round or oval with dispersed chromatin. There are abundant densely eosinophilic cytoplasmic inclusions that displace the nucleus towards the cell periphery. The rhabdoid elements usually merge with areas showing more conventional neuroendocrine morphology. Oncocytic variant has abundant densely eosinophilic cytoplasm (due to increased mitochondria), enlarged nuclei and prominent nucleoli. It can mimic hepatocellular carcinoma. Pleomorphic variant has bizarre enlarged hyperchromatic nuclei. Mitotic activity is not increased and there is no adverse effect on the prognosis. Clear cell variant of PanNET has clear cytoplasm due to large number of lipid vacuoles. It is often associated with von Hippel-Lindau syndrome or multiple endocrine neoplasia (MEN) type 1 or may be seen as a sporadic tumor. It may be misdiagnosed as metastatic renal cell carcinoma. Pigmented PanNET has dark brown/black cytoplasmic granules of lipofuscin pigment. They may mimic metastatic melanoma at first glance; however, melanocytic markers are negative. Rarer subtypes: Other rare histologic features include mucin production, spindle cell morphology, and psammoma bodies (often associated with somatostatinomas). Image courtesy of: Dr. Olca Basturk, Pancreatobiliary/Neuroendocrine Pathologist, Memorial Sloan-Kettering Cancer Center, New York; used with permission.