MKI67 and neoplasm: The Ki-67 index is calculated as the percentage of Ki-67–positive tumor cells in the areas of the highest density of Ki-67–positive cells, otherwise known as “hot spots.” To evaluate the Ki-67 index, the WHO classification requires 500–2000 tumor cells, while ENETS requires 2000 tumor cells (Rindi et al., 2006, 2007; Bosman et al., 2010).