Photo courtesy of ASH
ORLANDO, FL—After almost 10 years, during which time no new drug for acute myeloid leukemia (AML) has been approved, results of the RATIFY trial are available.
In this trial, investigators evaluated midostaurin in combination with chemotherapy for younger patients with FLT3-mutated AML.
Patients who received midostaurin in their regimen instead of placebo experienced significantly longer overall survival (OS) and event-free survival (EFS).
“The primary endpoint of the trial was overall survival—which was very important—uncensored for transplant,” said Richard Stone, MD, of Dana-Farber Cancer Institute in Boston, Massachusetts.
“This is very much a ‘real-world’ trial. We just took patients from the start and saw how they did until the end.”
Dr Stone presented results from the trial during the plenary session of the 2015 ASH Annual Meeting (abstract 6*).
Midostaurin (PKC412), developed as a VEGF and protein kinase C inhibitor, is a known FLT3 inhibitor that specifically inhibits the growth of leukemic cell lines.
As a multi-kinase inhibitor, its potency against FLT3 may be limited, but it is active against both ITD and TKD mutations. Because AML is polyclonal at diagnosis, a multi-targeted inhibitor may have an advantage in newly diagnosed AML.
As a single agent, Dr Stone explained, midostaurin produced few remissions in advanced, mutant AML. But when combined with chemotherapy in a phase 1B study in newly diagnosed patients, it produced encouraging results.
So members of the Alliance for Clinical Trials in Oncology, formerly CALGB, and many other cooperative groups around the world—the AMLSG, CETLAM, ECOG, EORTC, GIMEMA, NCIC, OSHO, PETHEMA, SAL, and SWOG—conducted a phase 3, randomized, double-blind trial of induction and consolidation with or without midostaurin in patients younger than 60 with newly diagnosed FLT3-mutated AML.
The primary endpoint was OS, and secondary endpoints were OS censored and uncensored at the time of transplant, complete remission (CR) rates, EFS, disease-free survival (DFS), and adverse events.
Mark Levis, MD, of Johns Hopkins Sidney Kimmel Comprehensive Cancer Center in Baltimore, Maryland, who introduced the plenary presentation, suggested that OS may not be the best primary endpoint for an AML trial, given the long time it takes to complete a trial like this.
He pointed out that, “while we waited for RATIFY to accrue and mature, our approach to the disease changed.” Allogeneic transplant is now often the favored consolidation.
Eligibility criteria
Patients aged 18 to 60 with normal end-organ function and documented AML were eligible to enroll. Patients could not have had acute promyelocytic leukemia.
Their FLT3 mutation had to be centrally determined prior to enrollment by 1 of 9 academic labs around the world, and results had to be obtainable within 48 hours of sample collection.
Patients could receive up to 5 days of hydroxyurea prior to the start of treatment while awaiting the results of the mutation analysis.
Trial design
Investigators randomized patients to induction of daunorubicin and cytarabine with either midostaurin or placebo.
Daunorubicin was administered at 60 mg/m2 by intravenous push on days 1-3, cytarabine at 200 mg/m2 per day on days 1-7, and midostaurin at 50 mg orally twice a day on days 8-21.
A second cycle of induction was given based on day 21 bone marrow biopsy.
When patients achieved CR, they went on to consolidation with high-dose cytarabine (3 g/m2 over 3 hours every 12 hours on days 1, 3, and 5) and either midostaurin at the same induction dose or placebo.
After up to 4 doses of consolidation, patients went on to maintenance therapy for 12 months. This consisted of placebo or midostaurin at the same dose twice daily on days 1-28.
Patient population
The investigators screened 3279 patients younger than 60 years with newly diagnosed AML and found 27% (n=887) to be FLT3-positive.
They randomized 717 patients—81% of the FLT3-positive patients—to either the midostaurin arm (n=360) or the placebo arm (n=357). These 717 patients were evaluable for the intent-to-treat analysis.
The median age was 47.1 (range, 19.0–59.8) in the midostaurin arm and 48.6 (range, 18.0–60.9) in the placebo arm. There were significantly more males in the midostaurin arm (48.1%) than in the placebo arm (40.6%, P=0.045).
And the arms were almost identical for FLT3 stratification. In the midostaurin group, 22.5% had FLT3 TKD (no ITD), 47.5% had an ITD allelic ratio (+/- FLT3 TKD) less than 0.7, and 30.0% had a ratio of 0.7 or more.
In the placebo arm, 22.7% had FLT3 TKD, and 47.6% and 29.7% had ITD allelic ratios less than and greater than 0.7, respectively.
Safety
Rash/desquamation was the only significant difference in grade 3-4 non-hematologic events between the arms, with 13% in the midostaurin arm and 8% in the placebo arm (P=0.02).
Other grade 3-4 non-hematologic events occurring in 10% of patients or more included, in the midostaurin and placebo arms, respectively: febrile neutropenia (81%, 82%), infection (40%, 38%), diarrhea (15%, 16%), hypokalemia (13%, 17%), pain (13%, 13%), other infection (12%, 12%), ALT/SGPT (12%, 9%), and fatigue (9%, 11%).
There were 18 deaths (5%) in the midostaurin arm and 19 (5.3%) in the placebo arm during induction and consolidation treatment.
Efficacy
OS was superior for patients randomized to midostaurin. The median survival was 74.7 months (range, 31.7-not estimable) in the midostaurin arm and 25.6 months (range,18.6-42.9) in the placebo arm (P=0.0076).
Overall, there were 357 deaths, 171 and 186 in the midostaurin and placebo arms, respectively.
The 5-year survival rate was 50.9% for midostaurin and 43.9% for placebo.
EFS was also superior for patients randomized to midostaurin (P=0.0032), at a median of 8.0 months for midostaurin and 3.6 months for placebo. The 5-year EFS was 27.5% for midostaurin and 19.3% for placebo.
The CR rates by day 60 were not significantly different between the arms, at 59% and 53% for midostaurin and placebo, respectively. And the median time to CR was the same in each group, at 35 days.
The survival benefit, both overall and event-free, was consistent regardless of whether the patients were FLT3-ITD high, low, or FLT3-TKD.
The OS and EFS benefits were also consistent in censored and uncensored analyses, despite the high stem cell transplant rate. Four hundred eight patients (57%) received a transplant, 212 in the midostaurin arm and 196 in the placebo arm.
“The trial was positive whether you censored the patients at transplant or you kept following them for the whole time,” Dr Stone said.
He concluded that this type of international collaborative AML study based on genotype at diagnosis is feasible to do. But it took “a lot of collaboration, a lot of cooperation, a lot of persistence, because the trial took a long time to conceive of, conduct, and analyze.”
*Data in the presentation differ from the abstract.