CTNI-51. A RANDOMIZED DOUBLE-BLIND PHASE 3 STUDY OF VORASIDENIB VS PLACEBO IN PATIENTS WITH MUTANT IDH1/2 DIFFUSE GLIOMA (INDIGO): EXPLORATORY ANALYSIS OF VARIANT ALLELE FREQUENCY AND PROGRESSION-FREE SURVIVAL

INTRODUCTION Vorasidenib is an oral, brain-penetrant, inhibitor of mutant isocitrate dehydrogenase (mIDH) 1/2 enzymes. The INDIGO study (NCT04164901) showed significantly improved radiographic progression-free survival (PFS) by blinded independent review committee (BIRC) with vorasidenib, compared with placebo, in patients with mIDH1/2 adulttype diffuse glioma (hazard ratio [HR] 0.39, 95% CI 0.27–0.56; one-sided P = 0.000000067 [Mellinghoff N Engl J Med 2023]). The key secondary endpoint of time-to-next-intervention was also met. METHODS In this double-blind Phase 3 study, patients aged ≥ 12 years with residual/recurrent grade 2 mIDH1/2 oligodendroglioma or astrocytoma, measurable non-enhancing disease, and no prior treatment for glioma were randomized 1:1 to receive vorasidenib 40 mg or placebo daily in 28-day cycles. An investigational clinical trial assay centrally confirmed IDH1 R132H/C/G/S/L or IDH2 R172K/M/W/S/G mutation variants. Pretreatment (archival) tumor tissue was analyzed by next-generation sequencing for CDKN2A/B homozygous deletion and other co-mutations (ACE Extended Cancer Panel). RESULTS As of Sep 6, 2022 (preplanned second interim analysis), 168 patients were randomized to vorasidenib and 163 to placebo (median age, 40.0 years; Karnofsky performance scale = 100, 53.5%; oligodendroglioma, 172; astrocytoma, 159; mIDH1, 315; mIDH2, 16). Two patient subgroups were defined by baseline IDH1/2 variant allele frequency (VAF): lower/higher than the median value (0.377). The median PFS results favored vorasidenib over placebo in both subgroups (low VAF, one-sided P = 0.0116; high VAF, one-sided P < 0.0001). Vorasidenib and placebo groups had similar and a low number of co-mutations in known/likely oncogenic genes at baseline (median number of co-mutations across both groups was 4). CDKN2A homozygous deletion was detected in only two participants (both in the placebo group). Additional data will be presented. CONCLUSION In the first randomized Phase 3 study of a targeted therapy in grade 2 mIDH1/2 glioma, vorasidenib prolonged median PFS by BIRC, relative to placebo, irrespective of IDH1/2 VAF.