MKI67 and pancreatic neuroendocrine tumor: The 2010 WHO classification categorized panNENs as grade 1 and grade 2 pancreatic neuroendocrine tumors (panNETs), and grade 3 pancreatic neuroendocrine carcinomas (panNECs), based on the Ki-67 index or the mitotic index (G1: Ki-67 < 3%, G2: Ki-67 3–20%, G3: Ki-67 > 30%).