Variation in Meningioma Recurrence Risk Estimates Across Observational Cohorts: the Influence of Calendar Time, WHO Classifications, Geographical Settings, and Healthcare Systems

Recurrence risk estimates underpin meningioma research, including molecular classification and clinical trial benchmarking, yet are often based on retrospective or historical data. The aim of this study was to assess the variation of recurrence risk estimates across calendar periods, WHO classification editions, geographical settings, and healthcare systems.thetermine We analyzed 4,111 patients with primary WHO-1/-2 meningiomas from 31 centers in 15 countries (1990–2019). Recurrence was defined according to local radiological assessment. The 5- and 10-year recurrence risks were estimated using regression standardization with inverse probability of censoring weights, adjusting for key clinical, surgical, and histopathological variables. Recurrence risk estimates varied across all domains examined. More recent calendar periods were associated with higher predicted recurrence risk, particularly for WHO-2 at 5 years (e.g., ≥ 2013 vs. ≤ 2007: RR 1.60, 95