Midostaurin shapes macroclonal and microclonal evolution of FLT3-mutated acute myeloid leukemia.

Despite the use of midostaurin (MIDO) with intensive chemotherapy (ICT) as the front-line treatment for FLT3-mutated acute myeloid leukemia (AML), complete remission rates are close to 60-70%, and relapses occur in over 40% of cases. Here we studied the molecular mechanisms underlying refractory/relapsed (R/R) situation in FLT3-mutated AML patients. We conducted a retrospective and multicenter study involving 150 patients with R/R AML harboring FLT3-ITD (n=130) and/or FLT3-TKD (n=26) at diagnosis assessed by standard methods. Patients were treated in front-line with ICT + MIDO (n=54) or ICT alone (n=96) according to the diagnosis date and label of MIDO. The evolution of FLT3 clones and co-mutations was analyzed in paired diagnosis-R/R samples by targeted high-throughput sequencing. Using a dedicated algorithm for FLT3-ITD detection, 189 FLT3-ITD microclones (allelic ratio [AR] < 0.05) and 225 macroclones (AR ≥ 0.05) were detected at both time points. At R/R disease, the rate of FLT3-ITD persistence was lower in patients treated with ICT + MIDO compared with patients not receiving MIDO (68% vs. 87.5%, P=0.011). In patients receiving ICT + MIDO, detection of multiple FLT3-ITD clones (referred to as "clonal interference") was associated with a higher FLT3-ITD persistence rate at R/R disease (multiple clones: 88% vs. single clones: 57%, P=0.049). Considering both treatment groups, if only 24% of FLT3-ITD microclones detected at diagnosis were retained at relapse, 43% of them became macroclones. Together, these results identify parameters influencing the fitness of FLT3-ITD clones and highlight the importance of using sensitive techniques for FLT3--ITD screening in clinical practice.

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