In 2017, a new WHO classification divided NENs in 3 types of well differentiated NETs (G1 NETs present <2 mitoses/10 HPF, Ki-67 index <3%; G2 NETs present 2 to 20 mitoses/10 HPF, and a Ki-67 index between 3% and 20%; grade 3 neuroendocrine tumors (G3 NETs) present more than 20 mitoses/10 HPF, and a Ki-67 proliferative index >20%), and 2 types of poorly differentiated NECs (small-cell type and large-cell type, with more than 20 mitoses/10 HPF, and a Ki-67 proliferative index >20%). This evidence concerns the gene MKI67 and neuroendocrine neoplasm.