CTNI-57. REAL-WORLD EVIDENCE OF THE FREQUENCY OF POST-SURGICAL INITIAL OBSERVATION IN PATIENTS WITH IDH-MUTANT GLIOMA

Abstract BACKGROUND After initial resection of IDH-mutant gliomas, initial observation is an option for low-risk patients, to postpone potential therapy-related toxicities without impacting survival. Since NCCN guidelines for risk stratification are considered controversial, we aimed to assess the frequency of initial observation in IDH-mutant gliomas using real-world evidence in the US. METHODS We evaluated Optum claims from 2016-2021 of patients age ≥12 with ICD-10 codes for incident glioma. Since ICD-10 does not distinguish IDH-mutant from IDH-wild type (GBM) gliomas, we excluded patients with factors indicative of GBM (age>60/ hypofractionated RT/ carmustine wafer/ tumor-treating fields) to create a baseline cohort. We then evaluated the subgroup age <40 (<40 cohort), who have higher IDH-mutant incidence. To distinguish initial observation from surgical recovery, we assessed time from index surgery to first intervention. When 90% of first interventions had occurred those still without intervention were considered to undergo initial observation. RESULTS The baseline and <40 cohorts comprised 5404 and 646 patients, respectively. In the baseline cohort, 56% had intervention by day 90 (most commonly concurrent chemoradiation); peak intervention rate was 60%. Initial observation rate was 44%. In the <40 cohort, 47% had an intervention by day 90; peak intervention rate was 52%. Initial observation rate was 53%. CONCLUSIONS In both cohorts ≥90% of patients with likely IDH-mutant gliomas not initiating treatment within 3 months post-surgery continued in active observation. Initial observation rates were 44-53%, well above the levels we had expected based on NCCN guidelines. The cohorts likely include some GBM patients, for whom observation is unaccepted, and therefore these rates may understate actual initial observation rates for IDH-mutant glioma patients. These findings suggest that clinicians and patients have chosen initial observation over existing treatments, evincing a need for additional treatment options for this younger group of patients with considerably long life expectancy.