PBRM1 and meningioma: However, in a recent case series of 850 patients with meningiomas that were grade 1 (220/850, 26%), grade 2 (441/850, 52%), and grade 3 (176/850, 20%) (13 cases were not graded due to inadequate specimens), only 16 had an inactivating mutation in PBRM1 (1.9%) (14).