IDH1 (BUT NOT IDH2) MUTATIONS CAUSE INFERIOR OUTCOME IN PATIENTS WITH AML WITH AN INTERMEDIATE-RISK CYTOGENETICS

Background
IDH1 and IDH2 are enzymes that catalyze the oxidative carboxylation of isocitrate to α?ketoglutarate in the Krebs cycle. Heterozygous mutations at IDH1 Arg132, IDH2 Arg140 and IDH2 Arg172 were found to cause loss of normal enzymatic function. IDH1 mutations are described in 6?16% of patients with cytogenetically normal AML, incidence of IDH2 mutations is slightly higher (15?20%). IDH2 mutations, particularly Asp140 are considered to have an unfavourable prognostic impact.

Aims
Patients: Presence of IDH1 and IDH2 mutations was analysed in 296 patients with AML with an intermediate-risk cytogenetics (defined according to Grimwade et al., Blood, 2010) diagnosed between years 1998-2012. Median age at diagnosis was 55.1 years (range 16.0-81.7), the initial median WBC count was 22.3 x 10⁹/L (range 0.4-483.7). The male/female ratio was 147/149 and the median of follow-up was 10.8 months.

Methods
Exons 4 of both IDH1 and IDH2 genes were amplified by RT-PCR; PCR products were treated by ExoSAP-IT reagent and directly sequenced. Obtained sequences were compared with wild type ones and mutations were identified.

Results
IDH1/2 mutations were detected in 81 (27.4%) from 296 patients, all but one mutations were heterozygous. IDH mutations were more frequent in female patients (P=0.055) and independent of age (P=0.395). IDH mutations were associated with mutated DNMT3A (P=0.0008), but not with FLT3/ITD (P=0.124). IDH1 mutations were found in 28 (9.5%) patients; 14/28 (50.0%) patients had Arg132His mutation, 9/28 (32.1%) Arg132Cys, 4/28 (14.3%) Arg132Ser and the remaining one had a Arg132Gly change. 6 of IDH1-positive patients had also FLT3/ITD. 53/296 (17.9%) cases carried mutations in IDH2 gene; the majority of them (39/53; 73.6%) had Arg140Gln mutation, 13/53 (24.5%) harboured Arg172Lys change and one patient carried a previously undescribed alteration Gly145Trp. 11/53 cases were FLT3/ITD positive. None of the IDH mutations influenced WBC counts at diagnosis. Neither IDH1, nor IDH2 mutation worsened the chance for reaching complete remission (CR): 15/27 (55.5%) IDH1-positive cases receiving standard induction treatment achieved CR as well as 30/47 (63.8%) cases with IDH2 mutation and 126/208 (60.6%) without any IDH alteration. 10/15 (66.7%) patients harbouringIDH1 mutation suffered a relapse, while only 59/125 (47.2%; P=0.362) cases without any IDH mutation and 9/30 (30.0%; P=0.009) carrying IDH2 change relapsed. The difference was more obvious, when FLT3/ITD positive cases were excluded from analysis (66.7% patients with IDH1 mutation relapsed vs. 37.5% relapsing cases with wt IDH and 26.1% of IDH2-positive ones). Patients with mutated IDH1 had significantly shorter overall survival (OS) than cases without this mutation (P=0.048) or cases with IDH2 mutation (P=0.026). OS 2 years after the diagnosis was 18.8% in cases with mutated IDH1, compared with 35.2% and 39.3% in patients without any IDH mutation and IDH2-positive ones, respectively.

Summary
We detected IDH mutations in 27.4% of patients with intermediate-risk cytogenetics. IDH1?positive patients had significantly shorter OS in comparison with IDH negative ones as well as comparing to IDH2-positive cases. This may result from a slightly lower CR rate on one hand and higher incidence of relapses in IDH1 group on the other. IDH2 mutations did not influence the prognosis of AML patients whatsoever.

Supported by Research project 00023736 of Ministry of Health of Czech Republic and grant RVO VFN64165.

Keyword(s): AML, Mutation, Prognosis

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