The research shows that “FLT3 inhibitors are most effective in patients who are minimal residual disease (MRD) positive before allo-HCT,” first author Richard Schlenk, MD, of Heidelberg (Germany) University Hospital and the German Cancer Research Center, Heidelberg, said in an interview.
The findings are from a post-hoc analysis of the phase 3, multicenter QuANTUM-First trial, which involved patients with the FLT3-ITD mutation, who make up about a quarter of those with AML and who can have shorter survival and increased risk of relapse, compared with patients without the mutation. The current post-hoc analysis of the trial was presented at the European Hematology Association 2023 Congress.
The trial, published in April in The Lancet, showed significant benefits in newly diagnosed patients with FLT3-ITD AML who were treated with quizartinib and standard induction and consolidation therapy and then continued on quizartinib as monotherapy for up to 3 years.
In the trial, quizartinib, combined with standard cytarabine and anthracycline induction and standard cytarabine consolidation chemotherapy, and continued as monotherapy following consolidation, was associated with a significant improvement in overall survival versus placebo (median 31.9 months versus 15.1 months, respectively; hazard ratio, 0.776; P = .0324).
For the post hoc analysis of the trial, the authors sought to evaluate if the effects were observed regardless of whether or not allo-HCT was received – which may not be recommended when patients go into remission after the first round of chemotherapy. The issue is important, as efficacy of other targeted therapy with the FLT3 inhibitors has been associated with allo-HCT treatment.
“Midostaurin, for example is mostly effective if [the drug] is followed by allo-HCT, and much less effective [no significant improvement] without allo-HCT,” Dr. Schlenk said.
The authors also sought to evaluate the relationship between minimal residual disease (MRD) prior to allo-HCT in FLT3-ITD and overall survival.
For the trial, 539 patients, with a median age of 56 were randomized to quizartinib (n = 268) or placebo (n = 271), and 147 patients (54.9%) in the quizartinib arm and 150 (55.4%) in the placebo arm achieved complete remission after induction. The rates of incomplete hematologic recovery (CRi) were 16.8% and 9.6%, respectively.
Of those achieving complete remission, 57.1% of patients on quizartinib and 48.7% of those receiving placebo underwent allo-HCT in the first complete remission. The median time to allo-HCT in the two groups was 3.5 months with quizartinib and 3.3 months for placebo.
Following the completion of allo-HCT, 61 patients (72.6%) receiving quizartinib and 36 (49.3%) receiving placebo started 3 years of continuation monotherapy.
In addition, 115 patients received allo-HCT outside of CR1, including 60 on quizartinib and 55 on placebo.
After adjustment for factors including region, age, and white blood count, patients treated with quizartinib treatment had a significantly higher overall survival (HR, 0.770; P = .0284), as did those receiving allo-HCT in CR1 (HR, 0.424; P < .0001).
Furthermore, patients receiving quizartinib had a longer overall survival regardless of whether they received allo-HCT in CR1 or not.
Of note, quizartinib-treated patients who were MRD positive prior to their allo-HCT transplant had a longer overall survival versus placebo (HR, 0.471); as did those who were MRD negative (HR, 0.717), to a lesser degree.
There were no new safety signals identified among patients undergoing allo-HCT.
Of note, cytomegalovirus infection was more common in the quizartinib group (11.8%) versus placebo (5.5%), while decreased appetite was less common with quizartinib (2.9%) versus placebo (12.1%).
Asked by an audience member about any risk of graft-versus-host disease (GVHD), Dr. Schlenk noted that “no difference between the quizartinib and placebo arms has been observed in GVHD acute and chronic.”
He added that patients “appear to benefit more from quizartinib if they have higher allelic frequency versus lower, overall,” and that younger patients, in general, showed greater benefit from quizartinib versus those over 60.
In general, “we see that for patients receiving allo-HCT transplantation, it’s beneficial to be randomized in the quizartinib arm [while] patients who did not undergo allo-HCT in first complete remission benefit equally when treated with quizartinib versus placebo,” he said in presenting the findings at the EHA meeting.
“And irrespective of pre–allo-HCT MRD status, longer survival was observed in those treated with quizartinib versus placebo, but most benefit was observed in those who were MRD positive.”
Quizartinib was approved in Japan this year in combination with chemotherapy for patients with newly diagnosed AML whose tumors harbor FLT3-ITD mutations.
The drug was granted a priority review by the U.S. Food and Drug Administration in October 2022. While the target action date was in April, a new decision date of July 21, 2023, is expected.
The study was sponsored by Daiichi Sankyo. Dr. Schlenk reported relationships with Daiichi Sankyo and other companies.