MIB1 and Atypical Meningioma: Expression of proliferation markers, such as MIB-1 and Ki-67, has generally shown progressive increases in the labeling index with a WHO grade from 1.00-1.35% for grade I to 1.90-9.30% for grade II or atypical meningiomas and 5.60-19.5% for grade III or anaplastic meningiomas [15,16].