SAN DIEGO – In patients with newly diagnosed acute myeloid leukemia (AML) bearing IDH1 or IDH2 mutations, combinations of either ivosidenib (Tibsovo, for IDH1) or enasidenib (Idhifa, for IDH2) with standard induction and consolidation regimens are safe and well tolerated and are associated with encouraging remission rates, results of a phase 1 trial indicate.
Dr. Eytan M. Stein
In the open-label, phase 1 trial, ivosidenib plus chemotherapy was associated with elimination of minimal residual disease (MRD) by flow cytometry in 88% of treated patients and with IDH1-mutation clearance in 41% of patients.
Enasidenib plus chemotherapy was associated with elimination of MRD in 45% of patients and with IDH2-mutation clearance in 25% of patients, said Eytan M. Stein, MD, from Memorial Sloan Kettering Cancer Center in New York.
“The overall survival rates are robust, with greater than 75% 1-year survival in both ivosidenib- and enasidenib-treated patients,” he said at the annual meeting of the American Society of Hematology.
Both ivosidenib and enasidenib are approved in the United States for treatment of patients with relapsed or refractory AML bearing either IDH1 or IDH2 mutations, respectively. In this trial, the investigators explored the therapeutic potential of the IDH inhibitors in patients with previously untreated disease.
Dr. Stein and his colleagues investigated combining each of the agents with standard induction therapy with either daunorubicin 60 mg/m2 per day or idarubicin 12 mg/m2 per day for 3 days, plus cytarabine 200 mg/m2 per day for 7 days. Patients with IDH1 mutations received ivosidenib 500 mg once daily, and those with IDH2 mutations received enasidenib 100 mg once daily.
After induction, patients with a complete remission (CR), CR with incomplete recovery of hematologic counts (CRi), or CR with incomplete recovery of platelets (CRp) could receive up to four cycles of consolidation therapy while continuing the IDH inhibitor. Patients who completed consolidation or were ineligible for consolidation could continue on maintenance therapy with their assigned drug until the end of the study.
The drugs were discontinued in patients who went on to hematopoietic stem cell transplant.
The most frequent co-occurring baseline mutations were DNMT3A, NPM1, and NRAS for patients with IDH1 mutations, and DNMT3A, SRSF2, and ASXL1 for patients with IDH2 mutations.
A total of 60 patients were assigned to ivosidenib and chemotherapy and 93 were assigned to enasidenib/chemotherapy. The median patient age was about 63 years in each arm.
All patients in each arm received a least one induction dose and about 48% in each arm received at least some consolidation dosing. In all, 18% of patients in the ivosidenib arm and 19% in the enasidenib arm went on to maintenance.
Treatment discontinuations occurred in 55% of patients in the ivosidenib group and 84% in the enasidenib group. The primary reason for discontinuation included HSCT, adverse events, progressive disease, and death (one and four patients in the respective arms).
Adverse events of interest, regardless of attribution, included the IDH differentiation syndrome in two patients on ivosidenib and one on enasidenib, leukocytosis, QT interval prolongation, and increased blood bilirubin.
The 30-day and 60-day mortality rates were 5% and 8% in the ivosidenib arm and 5% and 9% in the enasidenib arm, respectively.
Best overall response rates (CR+CRi+CRp) among all patients were 80% in the ivosidenib arm and 72% in the enasidenib arm. In each trial arm, the response rates were higher among patients with de novo AML, compared with secondary AML.
Of 12 ivosidenib-treated patients who had IDH1-mutation clearance, 10 had clearance at the end of induction therapy, and 2 achieved clearance during or after consolidation. Of 15 ivosidenib-treated patients who became MRD negative, 12 had achieved it by the end of induction, and 3 became MRD negative during consolidation.
In the enasidenib arm, 15 patients had IDH2 mutation clearance (11 after induction, 4 during consolidation) and 9 became MRD negative (7 after induction and 2 during or after consolidation).
The probability of surviving to 1 year after the start of induction among ivosidenib-treated patients was 79%; the median overall survival had not been reached and was not estimable at the time of data cutoff. The probability of surviving to 1 year among patients in the enasidenib arm was 75%. In this group, too, median overall survival had not been reached.
The clinical benefit of adding either IDH inhibitor to induction, consolidation, and maintenance therapy for patients with newly diagnosed AML with IDH mutations will be further evaluated in a randomized, phase 3 trial, Dr. Stein said.
The study was funded by Agios Pharmaceuticals and Celgene. Dr. Stein reported consulting with those companies and others.
SOURCE: Stein EM et al. ASH 2018, Abstract 560.
