AML-432 Overall Survival (OS) by IDH2 Mutant Allele (R140 or R172) in Patients With Late-Stage, Mutant-IDH2 Relapsed/Refractory Acute Myeloid Leukemia (AML) Treated With Enasidenib or Conventional Care Regimens (CCR) in the Randomized, Open-Label, Phase 3 IDHENTIFY Trial

Context: IDH2 mutations (mIDH2) occur in ~8%-19% of patients with AML, typically as R140Q (~75%) or R172K (~25%) point mutations, which have distinct functional effects and prognostic relevance. In the phase 3 IDHENTIFY trial, enasidenib did not significantly improve OS vs CCR in older patients with mIDH2 relapsed/refractory AML, but a trend for improved OS with enasidenib was detected in patients with IDH2-R172. Objective: Investigate molecular profiles and OS in mIDH2 variant subgroups (R140/R172). Methods: IDHENTIFY (NCT02577406) enrolled patients aged ≥60 years who had received 2-3 prior AML-directed therapies. Patients were randomized 1:1 to enasidenib 100-mg/day or CCR (azacitidine, intermediate- or low-dose Ara-C, or supportive care). Co-occurring mutations were identified by targeted NGS of BMMC DNA. Total 2-hydroxyglutarate was determined by LC/MS. Results: Of 319 patients enrolled, 88 (28%; 43 enasidenib, 45 CCR) had mIDH2-R172 and 229 (72%; 115 enasidenib, 114 CCR) had mIDH2-R140. Median baseline 2-hydroxyglutarate level and IDH2 VAF were similar between arms and mIDH2 subgroups. Patients with mIDH2-R172 had fewer baseline mutations (median 4 [range 2-8]) than those with mIDH2-R140 (5 [1-11]) (P<0.0001). Common co-mutations were SRSF2 and RUNX1 in the R140 cohort (59% each) and DNMT3A in the R172 cohort (57%). Compared with R172, R140 was enriched with SRSF2, FLT3 (-ITD/-TKD), NPM1, RUNX1, and JAK2, whereas DNMT3A and TP53 were more common with R172. In Cox multivariate analysis including mIDH2 variant, DNMT3A status, and number of baseline mutations, mIDH2-R172 was significantly correlated with improved OS (P=0.04 vs R140) in the enasidenib arm, and number of baseline mutations was significantly (P<0.01) associated with OS in the CCR arm. Median OS in the R172 subgroup was 14.6 months with enasidenib vs 7.8 months with CCR (HR, 0.59 [95%CI 0.35-0.98]; P=0.039); 1-year survival rates were 62% and 30%. In the R140 subgroup, median OS was 5.7 months in both arms (0.93 [0.70-1.24]; P=0.61), and 1-year survival rates were 29% and 25% with enasidenib and CCR. Conclusions: Mutational burden and co-mutational profiles differed between patients with mIDH2-R140 and mIDH2-R172 relapsed/refractory AML. In the R172 subgroup, median OS and 1-year survival rate with enasidenib were approximately double those with CCR.