Abstract Background: FMS-like tyrosine kinase 3 internal tandem duplication (FLT3-ITD) is one of the most frequent mutations in acute myeloid leukemia (AML), occurring in approximately 25–30% of adult cases and conferring an adverse prognosis through constitutive activation of FLT3 signaling, enhanced proliferation, and impaired differentiation of leukemic blasts. FLT3-ITD mutational burden, allelic ratio, insertion site, and co-mutations have been widely studied as prognostic markers. However, the impact of the number of distinct FLT3-ITD mutated clones—reflecting clonal heterogeneity—remains underexplored. Clonal diversity at diagnosis has been linked to therapeutic resistance and relapse in AML, yet limited data exist on whether multiple FLT3-ITD clones influence treatment outcomes. This study aimed to investigate the prognostic significance of FLT3-ITD clone numbers in a real-world cohort of FLT3-ITD–positive AML patients. Materials 52 received midostaurin in combination with daunorubicin plus cytarabine, while the remainder received standard anthracycline/cytarabine (7+3) induction without FLT3 inhibitor. Low-intensity regimens consisted of hypomethylating agent plus venetoclax or low-dose cytarabine with etoposide. In total, 168 patients (76.0%) were in the monoclone group and 43 patients (19.5%) were in the multiclone group. Among the multiclone group, 16.6% harbored two clones and 3.5% had three or more clones. Multiclone patients exhibited significantly higher bone marrow blast percentages at diagnosis (median 90% vs. 84%, p = 0.032). Median OS was shorter in the multiclone group compared with the monoclone group (1.6 years vs. 1.8 years, p = 0.046). Multivariable analysis confirmed multiclone status as an independent adverse factor for OS (HR 1.78, 95% CI 1.05–3.01, p = 0.032). Among patients undergoing allogeneic hematopoietic stem cell transplantation (allo-HSCT, n = 130), the negative prognostic impact of multiclone status persisted, particularly among those achieving morphologic CR prior to transplant (HR 2.05, 95% CI 1.10–3.82, p = 0.024). Initial induction response rates (composite complete remission CR, CR with incomplete platelet recovery, and CR with incomplete hematologic recovery) were similar between the monoclone and multiclone groups (53.9% vs. 51.9%, p = 1.0). However, the final response rate, including responses achieved after salvage therapy, was significantly lower in the multiclone group (54.8% vs. 73.1%, p = 0.026). The 2-year cumulative incidence of relapse was higher in multiclone patients (48.2% vs. 31.6%, p = 0.041), with correspondingly shorter relapse-free survival (median 9.8 vs. 15.4 months, p = 0.038). Conclusion: The presence of multiple FLT3-ITD mutated clones at diagnosis is associated with adverse clinical features, lower CR rates, and inferior OS in AML patients. The negative prognostic association persisted in post-HSCT outcomes. These findings highlight the potential of FLT3-ITD clonal heterogeneity as a biomarker for risk stratification and therapeutic decision-making in FLT3-ITD–positive AML. Although capillary electrophoresis–based fragment analysis has limitations in detecting minor subclones with very low allelic burden, it remains a valuable and practical method for assessing clonal heterogeneity in routine clinical practice. Future prospective studies integrating molecular co-mutation profiling and FLT3 inhibitor exposure are warranted to validate these observations and to develop targeted strategies for this high-risk subgroup.
Park et al. (Mon,) studied this question.