PATH-74. Concordance between cIMPACT-8 recommendations and Real World Meningioma Grade 2 Biologic Behavior

The fifth edition of the World Health Organization (WHO) Classification of Tumors of the Central Nervous System is the most recent revision aimed at improving the classification of meningiomas. A grade 2 designation for meningiomas can be based on multiple criteria, including a broad mitotic rate of 4–19 mitotic figures per 10 high-power fields, brain invasion, or three of five histologic features: spontaneous necrosis, prominent nucleoli, high cellularity, small cells with a high nuclear-to-cytoplasmic ratio, or sheet-like growth. Despite the addition of molecular grading parameters such as homozygous loss of CDKN2A/B and TERT mutations to these criteria, identifying grade 2 meningiomas that will behave aggressively from benign, indolent meningiomas remains challenging. As such, new guidance from cIMPACT-now update 8 further refines the grading parameters for meningiomas but has not yet been incorporated into the 2021 WHO classification. The need for postoperative radiation therapy for grade 2 meningiomas remains unresolved, and accurate grading is crucial. In this retrospective study, we aimed to determine the concordance rate between the cIMPACT-now update 8 predictive markers—specifically, combined chromosomal arm 1p deletion with 22q deletion and/or NF2 alteration—and grade 2 meningioma recurrence risk.