Refining prognostic stratification of atypical meningiomas: significance of chromosome 1p deletion and brain invasion

: Atypical meningiomas display heterogeneous clinical outcomes, necessitating prognostic markers to identify cases that would benefit of adjuvant treatment. This study investigated the prognostic value of chromosome 1p deletion, assessed by fluorescent in situ hybridization (FISH), in a cohort of 98 primary atypical meningiomas. The accuracy of FISH was validated by comparison with next-generation sequencing (NGS) results. Chromosome 1p deletion was significantly associated with parafalcine/tentorial location, high mitotic index, recurrence, and shorter recurrence-free survival (RFS). Multivariate analysis confirmed the presence of 1p deletion as an independent prognostic factor for shorter RFS. The study also evaluated the immunohistochemical expression of MCM2 and ACADL, which were more frequent in 1p-deleted tumors, but could not reliably predict 1p status. Brain-invasive otherwise benign (BIOB) meningiomas had significantly lower rates of 1p deletion, MCM2 expression, and recurrence, than mitotically active atypical meningiomas. However, recurring BIOB meningiomas showed higher frequencies of MCM2 expression, spontaneous necrosis, and 1p deletion, suggesting that these features may identify BIOB cases with a higher recurrence risk. In conclusion, FISH-detected 1p deletion is a reliable prognostic marker for atypical meningiomas, and its assessment, along with histopathological and immunohistochemical features, can refine the prognostic stratification of these tumors.