1. Identify clinical features specific to WHO grade II and III gliomas (LGG) with isocitrate dehydrogenase (IDH) mutations.

2. Determine whether there is a survival difference based on duration of adjuvant temozolomide (TMZ) among patients with IDH-mutant LGGs.

For glioblastoma, multiple studies demonstrate no survival benefit from greater than 6 cycles of adjuvant TMZ. Expectedly, prolonged use of TMZ is associated with greater toxicity. The current WHO classifications for CNS tumors distinguish IDH-mutant astrocytomas and oligodendrogliomas as distinct tumor types from glioblastoma. While the benefit of adjuvant TMZ has been demonstrated in LGG, the duration of TMZ necessary to maximize survival benefit in IDH-mutant LGGs is unknown. We aimed to characterize impact of adjuvant TMZ duration on overall survival (OS) and progression-free survival (PFS) among IDH-mutant LGGs.

Data was retrospectively collected from medical records of 259 patients with IDH-mutant LGGs treated within our institution. Integrated diagnoses were made based on the 2016 WHO classifications. Survival analysis was done with the Kaplan-Meier method and log-rank testing.

Among 259 patients with IDH-mutant LGGs, median PFS was 4.92 years and median OS was 19.13 years. Grade II gliomas had longer PFS (p=0.02) and OS (p<0.0001). 95 patients received adjuvant TMZ as part of their initial therapy. There was no significant difference in PFS or OS between those who received ≤6 vs >6 cycles, nor between those who received ≤10 vs >10 cycles.

Within our single center, retrospective cohort study, there was no statistical difference in survival outcomes between shorter and longer duration of adjuvant TMZ for IDH-mutant LGGs. The optimal duration of adjuvant TMZ for IDH-mutant LGG is unknown. This data suggests that duration of TMZ beyond 6 cycles does not provide additional survival benefit.