Outcome of AML Patients with IDH1 or IDH2 Mutations from Diagnosis and Refractory/Relapse Phase of the Disease in Routine Practice

Somatic mutations of isocitrate dehydrogenase 1 (IDH1) or 2 (IDH2) genes are found in 7-14% and 8-19% of AML. IDH1R132, IDH2R140 and IDH2R172mutations are most frequent in cytogenetically normal AML (25-30% of cases) and significantly associated with NPM1 mutations (except for IDH2R172). Their prognostic significance depends on mutational context (NPM1 and FLT3-ITD status) and on type of mutation: IDH1R132 has a possible adverse effect, IDH2R140 is associated with a favorable effect while the IDH2R172 effect remains controversial (Green C, Blood 2011; Papaemmanuil E, NEJM 2016). IDH1/2 mutations induce a neomorphic enzyme that overproduces the 2-hydroxyglutarate oncometabolite and thus have emerged as promising therapeutic targets. Indeed, AG-120 (IDH1 inhibitor) and AG-221 (IDH2 inhibitor) have shown encouraging activity in phase I trials including Rel/Ref AML pts though median OS are not yet reported. The prognosis of IDH mutated pts at this phase of the disease is not well described in routine practice outside clinical trials. The primary objective of this study was to describe characteristics and outcome of AML pts with IDH1/2 mutations treated in routine practice by intensive chemotherapy from both diagnosis and Rel/Ref phase of the disease.

This study included 1603 pts admitted at the Toulouse University Hospital and/or registered in the Oncomip regional Network from January, 1^st, 2000 to December, 31^st, 2014. This database included all cases of AML pts treated by intensive chemotherapy since 2000 then, starting from 2007, all consecutive patients whatever their treatment (Bories P, Am J Hematol 2014; Bertoli S, Blood 2013). Molecular analyses were performed at diagnosis or retrospectively from stored samples. Only first relapses after standard intensive chemotherapy were considered for this analysis and refractory disease was defined as failure following one course of induction chemotherapy including or not a second course for patients with more than 5% bone marrow blasts at day 15.

Treatment distributions were as follows: 984 pts received intensive chemotherapy, 224 azacitidine and 312 best supportive care. Mutational status of IDH1 and IDH2 was available for 465 pts of whom, 422 received intensive chemotherapy as first line therapy, 21 azacitidine and 20 BSC. The study focalized on pts treated by intensive chemotherapy: 349 IDH1/2wt (82%), 32 IDH1R132 (7.5%), 31 IDH2R140 (7.3%) and 11 IDH2R172 (2.6%). IDH2R140 (59y, IQR, 54-66.5) and IDH2R172 (60y, 42.5-64) pts were older than IDH1R132 (53y, 43.8-59.3) and IDHwt (52y, 39-62) pts. IDH2R172 pts had lower WBC count (2.1 G/l, 1.35-4.6) as compared to IDHwt (18 G/l, 4.3-66.9), IDH1R132 (14.7 G/l, 2.1-47.5) and IDH2R140 (21.5 G/l, 4.1-43). De novo AML was found in 85%, 94%, 74% and 73% of IDHwt, IDH1R132, IDH2R140 and IDH2R172 pts, respectively. Only 3 IDH1R132 and 3 IDH2R140 pts had unfavorable karyotype whereas 2 IDH2R140 pts had CBF-AML. Complete response was achieved in 80%, 91%, 74% and 100% of IDHwt, IDH1R132, IDH2R140 and IDH2R172 pts, respectively. Median overall survival (OS) from diagnosis was 23.6, 20.9, 35.8 and 41.1 months in IDHwt, IDH1R132, IDH2R140 and IDH2R172 pts, respectively. 185 Rel/Ref patients with IDH1/2-defined mutational status received salvage therapy with intensive chemotherapy (68%); azacitidine (18%) or other treatments (14%): 144 IDHwt (36 Ref/108 Rel), 18 IDH1R132 (3 Ref/15 Rel) and 23 IDH2R140/R172 (8 Ref/15 Rel). Complete response was achieved in 62 IDHwt (43%), 9 IDH1R132 (50%) and 12 IDH2R140/R172 (52%) pts, respectively. Median OS and 3-year OS from failure or relapse were: IDHwt: 7.6 months/19%; IDH1R132: 5.9 months/8% and IDH2R140/R172: 11 months/23%.

Observational data should be considered complementary to that provided by randomized clinical trials. They provide data collected in a non-selected general population, while participants in clinical trials are generally under very restrictive eligibility criteria. In refractory or relapsed patients who received salvage therapy, substantial differences may be observed according to the subtype of mutations, IDH1R132 having the poorest prognosis. IDH2R172 appears to confer a more favorable outcome (3-year OS from diagnosis: 61%).