Diagnostic Features and 2-Hydroxyglutarate (2-HG) Levels Among Acute Myeloid Leukemia (AML) Patients with and without Isocitrate Dehydrogenase (IDH) Mutations

Mutations in genes encoding isocitrate dehydrogenase 1/2 (IDH 1/2) enzymes result in increased 2-hydroxyguterate (2-HG) levels, which may provide a non-invasive marker of disease in IDH-mutant AML. The purpose of this study was to characterize patients with IDH-mutant AML by assessing presenting features, concurrent mutations, and 2-HG levels.

From 7-2011 through 6-2014, we identified 170 consecutive patients with newly diagnosed AML and measured 2-HG by liquid chromatography-tandem mass spectrometry in serum, urine, marrow aspirate, and marrow pellet samples. All patients had IDH1 R132, IDH2 R140 and R172 testing; 169/170 had hotspot mutational profiling for AKT1, APC, BRAF, CTNNB1, EGFR, ERBB2, KIT, KRAS, MAP2K1,NOTCH1, NRAS, PIK3CA, P53, and PTEN. We assessed FLT3 (168/170), NPM1 (168/170), CEBPA (100/170) mutational status as routine clinical care; 2 patients had BCR/ABL alterations, and 6 were JAK2 positive (of 36 tested). IDH1/2-mutant were compared to wildtype (WT) patients using a Wilcoxon rank sum test, Fisher's exact test, or Kruskal Wallis test, as appropriate.

The group was 54% male; 83% white, 2.4% black, 2.4% Asian, and 6.5% Hispanic. 12 patients had APL. IDH mutations included IDH1 R132C (n=10), IDH2 R172 (n=7), and IDH2 140Q (n=22). Other mutations included NPM1 (20.8%), FLT3-ITD (17.3%), FLT3-TKD (6.6%), NRAS (18.4%), TP53 (3%), KRAS (6.5%), and KIT (1.2%). CEBPA mutations occurred in 13 of 100 patients. IDH mutations (n=39) more frequently co-occurred with normal cytogenetics and NPM1 mutations, vs IDH-WT, consistent with prior reports (Table 1). No patients with favorable cytogenetics harbored an IDH1/2 mutation.

Significantly higher 2-HG levels were detected among those with IDH1/2 mutations compared to IDH WT, in the serum (p<0.0001), urine (p<0.0001), marrow aspirate (p<0.0001) and marrow pellet (p<0.0001). Overall, elevated 2-HG levels were present regardless of type of IDH mutation. Serum and marrow pellet 2-HG levels were elevated (> 1000 ng/mL in serum and > 1000ng/2x10^6 cells in marrow pellet) in 30/38 and 24/29 IDH-mutant patients, respectively, compared to 1/129 and 5/117 IDH WT patients. All but 2 IDH-mutant patients displayed either or both an elevated marrow pellet or serum 2-HG. Patients with IDH2 R172 mutations had lower marrow 2HG levels compared to those with R140Q mutations (Figure 1, p=0.0434). The WBC and blast count was lower among IDH2 R172-mutant compared to R140Q- or IDH1 R132C-mutant patients (p= 0.0134 and p=0.0039, respectively); there was no significant difference in serum 2HG levels.

All three canonical IDH1/2 mutations have higher 2HG levels compared to IDH WT. IDH2 R172 mutated AML may present with lower WBC counts and peripheral blast percentage compared to IDH1 R132C and IDH2 R140Q mutant AML. Urine and serum 2HG levels effectively identify patients with mutant IDH1/2, of particular relevance given targeted therapies for these mutations.

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