The research was presented at the European Hematology Association Hybrid Congress 2023.
For the study, AML patients with the most common form of mutation in the proto-oncogene fms-like tyrosine kinase 3 (FLT3), known as the internal tandem duplication (ITD), were randomized to 24 months of maintenance therapy with either the FLT3 inhibitor gilteritinib or placebo.
The trial did not meet its primary endpoint, as there was no significant difference in relapse-free survival (RFS) between those assigned to the active drug and those given placebo, and there was no difference in overall survival rates.
However, subgroup analysis revealed that FLT3/ITD AML patients who were MRD+ after transplant, which represented approximately half of the participants, experienced a significant 48% improvement in RFS with gilteritinib versus placebo, while no benefit was seen in MRD– patients.
While acknowledging that the trial did not meet its primary endpoint, presenter Mark J. Levis, MD, PhD, program leader, hematologic malignancies and bone marrow transplant program, Johns Hopkins Sidney Kimmel Comprehensive Cancer Center, Baltimore, said it was nevertheless “a successful study.”
“We learned how to use these drugs and in whom,” he continued, adding: “No, not everybody needs and should get a FLT3 inhibitor post-transplant, but we can use this [MRD] assay to identify who.”
Consequently, Dr. Levis believes that gilteritinib “should be a standard of care for those who are MRD positive,” although the decision to use it “should be balanced against the potential for toxicity,” compared with not adding an additional treatment after HCT.
He told a press conference that “we’re going to certainly make sure that patients who are MRD positive get [gilteritinib],” although the MRD negative patients “are going to be more questionable,” especially because the assay that they used in the study is not “perfect.”
Dr. Levis also suggested that the trial did not meet its endpoint because of regional differences in the clinical practice, such as in the number of treatment cycles prior to HCT, the time to transplant, and the previous use of a FLT3 inhibitor, all of which may have skewed the findings.
“Everybody in the world is convinced that they’re the best transplanter,” he said, and yet “they all do it differently, and the heterogeneity is astounding.”
He added: “If we’d restricted everybody [to a] pretransplant regimen, I suspect we would have had a different result than what we’re getting here, but this is releasing the drug into the world and saying: ‘Here, transplant however you want, however it’s practiced in the real world. Tell us how this works.’ ”
Approached for comment, Claudio Brunstein, MD, PhD, vice-chair of the department of hematology and oncology in the Cleveland Clinic Taussig Cancer Institute, said that while there was “some disappointment” with the results, he was “not surprised” that the trial did not meet its primary endpoint.
He said in an interview that the patient population was not of “high enough risk” to demonstrate an overall difference between gilteritinib and placebo, although he conceded that it is “hard to get to high-risk patients in a timely way” and so conduct a trial with them.
As to the notion that variations in clinical practice could have been responsible, Dr. Brunstein pointed out that it was a randomized trial, so the issue would have applied equally to both sides.
He nevertheless believes that it is “a very important study,” and “just the fact that it was done in the context of a number of drugs coming and being approved by the [U.S. Food and Drug Administration] in AML is quite remarkable.”
This is especially the case given that “many centers are already using [gilteritinib] as off-label maintenance therapy.”
Dr. Brunstein added that it is “good news” that the drug was effective in MRD+ patients, as it shows “you can overcome that with maintenance therapy rather than keeping giving more and more chemotherapy, especially as there are patients you’re worried about giving more intensive chemotherapy to make them MRD negative.”
He pointed out, however, that the assay used in the trial was “research grade” and very sensitive to MRD and “is not available everywhere, so there is an adjustment that the community will have to do to in order to apply this data.”
“But for those who are more obviously MRD positive with less sensitive assays, gilteritinib is already something that can be used,” Dr. Brunstein said.
Presenting the findings, Dr. Levis stated: “We all know that patients with FLT3/ITD AML have a high risk of relapse and are routinely referred for transplant. And we know that the detection of measurable residual disease pretransplant is highly predictive of outcome post-transplant.”
He continued that FLT3 inhibitors are “routinely given as post-transplant maintenance ... based on some prior trials, mostly with sorafenib.”
“But uncertainty exists as to the broad applicability of these trials,” Dr. Levis said. Moreover, the use of sorafenib in this context is “off label and can be difficult to tolerate,” and “we know that most patients are cured with allogeneic transplant alone.”
Gilteritinib is already known to be well tolerated as a monotherapy, and was approved by the FDA for the treatment of adult patients with FLT3 mutation–positive relapsed or refractory AML in 2018.
The investigators therefore examined whether it would be beneficial as a post-HCT maintenance therapy in FLT3-ITD AML. Patients were required to be in morphologic remission after one or two courses of induction therapy, with Dr. Levis underlining: “We did not allow patients who had been salvaged onto the study.”
They subsequently had a marrow aspirate sample taken for MRD analysis before undergoing allogeneic transplant, with any conditioning regimen, donor, or graft-versus-host disease (GVHD) prophylaxis allowed.
Between 30 and 90 days later, patients with successful engraftment who were able to take oral medication were then randomized to 24 months of maintenance therapy with either gilteritinib or placebo.
Dr. Levis showed that, among 620 patients screened at 110 centers in 16 countries, 356 were randomized between Aug. 15, 2017, and July 8, 2020. The median age was 53 years, and 49% of gilteritinib patients and 48% of those given placebo were female.
He noted that there was a “fairly even global distribution” of patients from North America, Europe, and the Asia/Pacific region, and that 60% of patients underwent a myeloablative conditioning regimen. Approximately the same proportion had received an FLT3 inhibitor prior to HCT.
MRD positivity, assessed at a cell count of ≥ 10-6, was observed pre-HCT in 47% of patients in both treatment groups, and in 50% of gilteritinib patients and 51% of placebo patients at both pre- and post-transplant assessments.
The treatment regimen was completed by 52.8% of patients assigned to gilteritinib and 53.9% in the placebo arm. Dr. Levis said that 18.5% and 20.3% of patients, respectively, experienced a grade 3/4 treatment emergent acute GVHD event, while 32.6% and 21.5%, respectively, had a grade ≥ 3 treatment emergent infection.
He noted that “adverse events were clearly more common in the gilteritinib arm and often led to either dose reduction or interruption, or withdrawal of treatment.”
The most common grade ≥ 3 treatment emergent adverse event was a decrease in neutrophil count, seen in 24.7% of gilteritinib patients and 7.9% of those given placebo, followed by reduced platelet count, in 15.2% and 5.6%, respectively, and anemia, in 6.2% and 1.7%, respectively.