Ki-67 is expressed exclusively in proliferating cells [58, 59], with the Ki-67 labeling index (Ki-67 LI; % of cells expressing Ki-67) correlating closely with histological tumor grade in gliomas [14, 60–64] and a Ki-67 LI of 10% being regarded as a reliable criterium for malignancy [65, 66]. The gene discussed is MKI67; the disease is neoplasm.