CNSC-21. DORMANCY IN THE NATURAL HISTORY OF IDH MUTANT GLIOMAS BEFORE AND AFTER RESECTION: A RETROSPECTIVE COHORT STUDY

Abstract BACKGROUND Natural history and growth dynamics of isocitrate dehydrogenase (IDH)-mutant gliomas has not been well studied in the post-IDH era. While existing paradigms assume continuous linear growth, our clinical observations suggest these tumors often exhibit saltatory growth and prevalence of dormancy periods. Knowledge of growth patterns may have significant implications for treatment timing. This study evaluates the natural history of IDH-mutant gliomas who did not receive adjuvant therapy. METHODS We conducted a retrospective analysis of a single physician’s cohort of adults with pathologically confirmed IDH-mutant gliomas that were followed in neuro-oncology clinic from 2019 to 2025. Growth pattern was assessed for patients before and/or after surgical intervention who had serial surveillance imaging (MRI brain) available for more than 1 year. Patients that received adjuvant treatments were ineligible. Tumor growth was assessed using manual two-dimensional (2D) linear measurements on serial T2-fluid attenuated inversion recovery (FLAIR) MRI sequences, defining dormancy as non-measurable (less than 2 mm growth) over at least one year. RESULTS Our analysis identified prevalence of dormancy both pre-resection and post-resection. Among three eligible pre-resection patients, two patients with astrocytoma demonstrated dormancy durations of 15 and 120 months and continuous growth was seen in one patient with oligodendroglioma. Among ten eligible post-resection patients, 80% exhibited at least one dormancy period. Oligodendrogliomas had a median dormancy duration of more than 36 months while astrocytomas showed more variable growth, with half exhibiting dormancy and half continuous growth. Heterogeneity in growth patterns was observed, with periods of stability interspersed with slow progression. CONCLUSION Our results indicate that saltatory growth is a common feature of IDH-mutant gliomas, highlighting the need to reevaluate growth benchmarks in clinical decision-making. In alignment with SNO/EANO guidance, continued surveillance and individualized management are essential and may allow deferral of adjuvant therapy, particularly in indolent cases.