MKI67 and neoplasm: Pancreatic NETs may be classified according to stage/disease extent (localised, regional or metastatic) and according to the histological grade using the Ki67 proliferation index from slower growing G1 and G2 tumours (G1/G2; Ki67 index <3% and 3-20% respectively) through to faster growing (well differentiated) G3 tumours (Ki67 index >20%) (14).