Cytopathology in focus—Low-grade pancreatic neuroendocrine tumors in small samples: Grading challenges
August 2024—Two to five percent of pancreatic tumors are pancreatic neuroendocrine neoplasms, of which more than 90 percent are well-differentiated pancreatic neuroendocrine tumors (PanNETs). The current World Health Organization classification stratifies PanNETs into three histological grades based on mitotic count and Ki-67 proliferation index. Low-grade PanNETs (grades one and two) are morphologically indistinguishable and have characteristic neuroendocrine cytomorphologic features: a dispersed/loosely cohesive smear pattern composed of small-to-medium monomorphic cells with occasional plasmacytoid appearance; amphophilic, granular, or vacuolated cytoplasm; round nuclei; and coarse salt-and-pepper chromatin.