MKI67 and neuroendocrine neoplasm: According to 2019 WHO classification, based upon the Ki-67 index and morphology, gastro-entero-pancreatic (GEP) NENs are subdivided into four categories: well-differentiated G1 neuroendocrine tumors, with a Ki-67 index below 3%, G2 neuroendocrine tumors, with a K-67 between 3% and 20%, G3 neuroendocrine tumors, with a well-differentiated morphology and a Ki-67 index above 20%, and poorly differentiated neuroendocrine carcinomas (NECs), with a poorly differentiated morphology and a Ki-67 above 20% [7].