The following categories were created based on Ki-67 proliferation index: NET G1 (with the Ki-67 less than 3%), NET G2 (with the Ki-67 proliferation index ranging from 3% to 20%), and NET G3 (with Ki-67 between 20% and 55%); and a group of low-differentiated cancers: NEC (with a Ki-67 proliferation index above 55%). Here, MKI67 is linked to cancer.