Molecular Features Associated with Response to Enasidenib Plus Azacitidine in Newly Diagnosed IDH2-Mutated Acute Myeloid Leukemia

IDH2 gene mutations, typically at residues R140 and R172, occur in 8–19% of patients with acute myeloid leukemia (AML). These mutations induce production of 2-hydroxyglutarate (2-HG), an oncometabolite that causes DNA and histone hypermethylation, and subsequent blockade of hematopoietic cell differentiation. In a phase 1b/2 trial (NCT02677922), combination therapy with azacitidine + enasidenib significantly improved overall response rate compared with azacitidine only therapy (74% vs 36%; P<0.001) in patients with newly diagnosed IDH2-mutated AML not eligible for intensive chemotherapy. We investigated the association between molecular features and clinical outcomes from that trial. In all, 101 patients were randomized to enasidenib + azacitidine (n=68) or azacitidine only (n=33); 74% of patients had IDH2-R140. Baseline 2-HG levels and IDH2 variant allele frequency (VAF) were similar between treatment arms and IDH2 variants and were not significantly different between clinical response categories. Significant 2-HG and IDH2 VAF reductions from baseline were observed with combination therapy compared with azacitidine only. Molecular profiling revealed SRSF2 preferentially co-mutated with IDH2-R140, and DNMT3A co-mutated with IDH2-R172. IDH2 VAF was reduced to <1% in 50% of patients who achieved CR with combination therapy (18/36) and azacitidine only (2/4). VAFs of genes in the DNA methylation, receptor-tyrosine-kinase, and RAS canonical pathways were reduced in patients achieving CR. Of note, combination therapy improved event-free survival in patients with RAS-pathway mutations, which have been associated with resistance to enasidenib monotherapy.