ORIGINAL ARTICLE The prognostic impact and stability of Isocitrate dehydrogenase 2 mutation in adult patients with acute myeloid leukemia W-C Chou 1,2,4 , W-C Lei 2,4 , B-S Ko 2 , H-A Hou 2 , C-Y Chen 2 , J-L Tang 2 , M Yao 2 , W Tsay 2 , S-J Wu 2 , S-Y Huang 2 , S-C Hsu 1 , Y-C Chen 1 , Y-C Chang 1 , K-T Kuo 3 , F-Y Lee 3 , M-C Liu 3 , C-W Liu 3 , M-H Tseng 2 , C-F Huang 2 and H-F Tien 2 1 Department of Laboratory Medicine, National Taiwan University Hospital, Taipei, Taiwan; 2 Department of Internal Medicine Division of Hematology, National Taiwan University Hospital, Taipei, Taiwan and 3 Department of Pathology, National Taiwan University Hospital, Taipei, Taiwan Although the clinical features of the Isocitrate dehydrogenase 2 (IDH2) mutation in acute myeloid leukemia (AML) have been characterized, its prognostic significance remains contro- versial and its stability has not been investigated. We analyzed 446 adults with primary non-M3 AML and found IDH2 R172, R140 and IDH1 R132 mutations occurred at a frequency of 2.9, 9.2 and 6.1%, respectively. Compared with wild-type IDH2, mutation of IDH2 was associated with higher platelet counts, intermediate-risk or normal karyotype and isolated þ 8, but was inversely correlated with expression of HLA-DR, CD34, CD15, CD7 and CD56, and was mutually exclusive with WT1 mutation and chromosomal translocations involving core-binding factors. All these correlations became stronger when IDH1 and IDH2 mutations were considered together. Multivariate analysis revealed IDH2 mutation as an independent favorable prognostic factor. IDH2  /FLT3-ITD þ genotype conferred espe- cially negative impact on survival. Compared with IDH2 R140 mutation, IDH2 R172 mutation was associated with younger age, lower white blood cell count and lactate dehydrogenase level, and was mutually exclusive with NPM1 mutation. Serial analyses of IDH2 mutations at both diagnosis and relapse in 121 patients confirmed high stability of IDH2 mutations. In conclusion, IDH2 mutation is a stable marker during disease evolution and confers favorable prognosis. Leukemia (2011) 25, 246–253; doi:10.1038/leu.2010.267; published online 16 November 2010 Keywords: IDH1; IDH2; acute myeloid leukemia Introduction The increasing number of genetic alterations discovered in acute myeloid leukemia (AML) has not only increased our under- standing of this heterogeneous disease but also provided prognostic information through which individualized treatment for the best interests of patients may become possible. These impacts of genetic mutations have been underscored by the inclusion of NPM1 and CEBPA mutations in the 2008 World Health Organization classification of AML. Among these genetic alterations, mutations of Isocitrate dehydrogenase 1 (IDH1) and IDH2, which encode two isoforms of isocitrate dehydrogenase, are special in that these genes are involved in metabolism, 1,2 rather than signaling pathways or transcription factors, which are commonly deranged in AML. The clinical and biological characterization of IDH mutations in myeloid malignancies have been reported in several studies. IDH mutations occur at low frequencies (3.6–5%) in myelodys- plastic syndrome, 3,4 and in chronic-phase myeloproliferative neoplasm (about 1.8%), 5,6 but obviously increased as these diseases progress to AML (7.5–21%), 3–6 indicating a role of IDH mutations in leukemogenesis. In AML, IDH2 mutations occur more frequently than IDH1 mutations, with frequencies of 11 vs 6% in patients younger than 60 years, 7 15.4 vs 7.7% in total patients, 8 and 19 vs 14% in adults with normal karyotype. 9 Although IDH1 and IDH2 proteins locate differently, in cytosol and mitochondria, respectively, they both function to generate a-ketoglutarate and are supposed to control redox status in cells. 10,11 The IDH mutants gain the neomorphic enzyme activity and lead to the production of an onco-metabolite, 2-hydroxyglutarate (2-HG), which was speculated to upregulate hypoxia-inducing factor 1a by inhibition of prolyl hydroxylase. 1,2,10,12 On the basis of the in vivo functions of IDH1 and IDH2, it is intuitive to expect similar clinical and biological characteristics between AML bearing mutations of these two genes. Indeed, mutations of both genes are more commonly present in patients with normal cytogenetics. 7,13–17 However, different features between IDH1-mutated and IDH2-mutated AML were shown in several reports, and even there existed differences between IDH2 R140 and R172 mutations. 9,17,18 In addition, the prognostic implications of these mutations also varied widely among different institutions. 7,15,17 More perplexingly, IDH2 R172 mutation alone was found to have distinct gene- and microRNA-expression profiles, 9 and appeared to be an inde- pendent poor prognostic factor. 18 In contrary, results from two studies suggested a possible favorable impact of IDH2 mutation in subgroups of AML patients. 7,8 Overall, the prognostic implication of IDH2 mutation is still controversial. Moreover, the side-by-side comparison is needed to delineate the similarities and distinctions among mutations at IDH1 R132, IDH2 R140 and IDH2 R172. Finally, the stability of IDH2 mutation remains uninvestigated. We have previously reported the clinical and biological characteristics of AML patients with IDH1 mutation at R132. 14 To further clarify the above issues of IDH1 and IDH2 mutations in AML, we then analyzed 446 adults with non-M3 AML in our institute. We found that IDH2 mutations were associated with some distinct biological features and implicated a longer overall survival (OS) in all non-M3 patients and in those with a normal karyotype. Moreover, IDH2 mutation was an independent favorable prognostic factor in multivariate analysis. Finally, by a comprehensive sequential study, we confirmed that IDH2 mutation, like IDH1 mutation we previously described, 14,19 was a stable mutation during disease evolution. Received 19 August 2010; revised 13 September 2010; accepted 8 October 2010; published online 16 November 2010 Correspondence: Dr H-F Tien, Department of Internal Medicine, National Taiwan University Hospital, Taipei 100, Taiwan. E-mail: hftien@ntu.edu.tw or Dr W-C Chou, Department of Laboratory Medicine and Internal Medicine, National Taiwan University Hospital, Taipei 100, Taiwan. E-mail: wchou@ntu.edu.tw 4 These authors contributed equally to this work. Leukemia (2011) 25, 246–253 & 2011 Macmillan Publishers Limited All rights reserved 0887-6924/11 www.nature.com/leu