CDKN2A and meningioma: In G1 meningiomas, the Ki-67 labeling index higher than 4% and higher than 20% has been found to correlate with higher recurrence rates respectively similar to G2 and G3 meningiomas.5 Unlike previous classifications, mutations in the TERT promoter and homozygous loss of CDKN2A define a WHO (G3) meningioma, irrespective of histotype.