CHICAGO—The investigational drug ivosidenib, an inhibitor of the mutant IDH1 enzyme, achieved complete remission (CR) rates of 32% and an overall response rate of 42% in relapsed/refractory (R/R) patients with acute myeloid leukemia (AML) and IDH1 mutation, according to investigators.

In addition, overall survival (OS) in patients who achieved CR more than doubled compared with those in the overall study population.

Fewer patients with CR had febrile neutropenia and infectious complications, and 25% of patients with CR were able to clear the IDH1 clone.

Duration of response was 6.5 months with the investigational drug.

Investigators reported the grade 3/4 toxicities could be managed with supportive care, were not fatal, and some patients still achieved responses.

IDH1 mutation, first identified almost 10 years ago with the sequencing of the first AML cancer genome, is a recurrent mutation in over 10% of patients with AML.

Mutated IDH1, reported in several malignancies, results in impaired cellular differentiation. Ivosidenib is a first-in-class oral therapy designed to inhibit the mutant IDH1 enzyme.

Phase 1 study (NCT02074839)

The phase 1 dose-escalation and dose expansion study specifically enrolled patients with R/RAML with mutated IDH1.

Daniel A. Pollyea, MD, of the Colorado University School of Medicine in Aurora, reported the data from 2 of the dose expansion cohorts as well as 35 patients from the dose escalation cohort at the 2018 ASCO Annual Meeting (abstract 7000).

All patients received ivosidenib 500 mg daily.

CR/CRh (CR with partial hematologic recovery; defined as morphologic remission with recovery of neutrophils to at least 500/mm3 and recovery of platelets to at least 50,000/µL) was the primary efficacy endpoint.

Of 179 patients in the primary efficacy cohort, 10% were still receiving treatment at the time of the presentation.

While most patients discontinued due to disease progression, 10% came off therapy for stem cell transplantation. Median duration of treatment was 4 months.

Patients were a median 67 years of age. Approximately 1/3 had secondary AML.

Patients had received a median of 2 prior therapies and approximately 1/4 had relapsed after transplantation.

Fifty-nine percent were refractory to induction or reinduction therapy.

Toxicity

Dr Pollyea considered adverse events to be as expected for a relapsed/refractory AML population.

However, he called out 3 for special mention—leukocytosis, ECG QT prolongation, and IDH differentiation syndrome—none of which was fatal.

Eight percent of patients had grade 3 or 4 leukocytosis, some of which were mechanistically induced from treatment.

About 10% of patients had grade 3 or 4 QT prolongation.

And grade 3 or 4 differentiation syndrome was reported for approximately 5% of patients.

In 19 patients with any grade differentiation syndrome, CR was reported for 5 patients. The message: patients experiencing this adverse event can be managed with supportive care, continue treatment, and still respond.

All adverse events were managed with supportive care measures, including concomitant medications, and ivosidenib dose modifications as required.

CR/CRh was 32% for the efficacy cohort; median time to response was 2 months and median time of response was 8.2 months. CR rate was 24%. Investigator-reported International Working Group categorized ORR was 42%.

The median OS was 9 months for the entire cohort and 18.8 months for patients who achieved CR/CRh.

Dr Pollyea reported that transfusion independence—defined as no need for transfusion for 56 days—was achieved in all CR patients, 75% of CRh patients, and even in a proportion of nonresponders.

Investigtors observed febrile neutropenia and grade 3 or 4 infectious complications in fewer patients who achieved CR/CRh.

Of note was the observation that 23% of patients who achieved CR/CRh were able to clear the mutant IDH1 clone. Patients who did not respond still harbored the IDH1 clone, Dr Pollyea reported.

These results reported at ASCO are an update from those simultaneously published in NEJM.

The study was supported by Agios Pharmaceuticals.

Ivosidenib is being evaluated alone and in combination in other clinical trials.

Ivosidenib active in R/R IDH1-mutated AML patients