Real-World Outcomes of FLT3 Inhibitors in Acute Myeloid Leukemia, a Multicenter Study

María Argüello Marina. (2025). Real-World Outcomes of FLT3 Inhibitors in Acute Myeloid Leukemia, a Multicenter Study. MAR Oncology and Hematology. (2025) 5:08 Real-World Outcomes of FLT3 Inhibitors in Acute Myeloid Leukemia, a Multicenter Study María Argüello Marina, MD¹, Irene Arnaiz Martin, MD², Guzmán López de Hontanar Torres, MD³ María Ángeles Foncillas, MD⁴ ¹Hospital Universitario de Guadalajara, Guadalajara, Spain. ²Hospital Universitario de Getafe, Getafe, Spain. ³Hospital Universitario Príncipe de Asturias, Alcalá de Henares, Spain. ⁴Hospital Universitario Infanta Leonor, Madrid, Spain. *Correspondence to: María Argüello Marina, MD, Hospital Universitario de Guadalajara, Guadalajara, Spain. Copyright. © 2025 María Argüello Marina This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Received: 21 Aug 2025 Published: 25 Aug 2025 MAR Oncology and Hematology (2025) 5:08 Research Article María Argüello Marina, MAR Oncology and Hematology (2025) 5:08. Page 2 of 14 María Argüello Marina. (2025). Real-World Outcomes of FLT3 Inhibitors in Acute Myeloid Leukemia, a Multicenter Study. MAR Oncology and Hematology. (2025) 5:08 Abstract Background: Acute myeloid leukemia (AML) with FLT3 mutations carries a poor prognosis. FLT3 inhibitors, such as midostaurin, combined with standard chemotherapy, have shown improved outcomes for FLT3-mutated AML patients. However, real-world data on their efficacy and safety are limited. This study assesses midostaurin's real-world efficacy, the timing of molecular diagnosis, and the impact of antifungal prophylaxis management. Methods: This retrospective multicenter study was conducted across four Spanish hospitals, including 15 patients with FLT3-mutated AML treated between 2019 and 2024. Data on demographics, clinical characteristics, diagnostic timelines, and treatments were collected and analyzed. Results: The average time to obtain FLT3 mutation results was 13.3 days, exceeding the recommended 8-day window per PETHEMA, NCCN, and ELN guidelines, and delaying midostaurin initiation to a mean of 24.5 days post-diagnosis. Despite these delays, 80% of patients achieved complete remission (CR), with 62.5% attaining negative minimal residual disease (MRD) status post-induction. Antifungal prophylaxis was administered to 60% of patients, primarily with posaconazole (62.5%), without midostaurin dose adjustments. Alternative antifungals (micafungin or fluconazole) were used to avoid CYP3A interactions per PETHEMA recommendations. No significant differences in adverse event rates were observed between antifungal regimens. Conclusion: The real-world use of midostaurin demonstrates efficacy comparable to clinical trials. However, delays in FLT3 mutation testing hinder adherence to treatment initiation guidelines, potentially impacting outcomes. Additionally, the lack of robust evidence regarding interactions between midostaurin and antifungal agents highlights the need for standardized antifungal prophylaxis strategies in FLT3-mutated AML. Addressing these challenges is essential to optimize outcomes in real-world settings. Key words: Acute myeloid leukemia; FLT3 mutation; Midostaurin; Real-world evidence; Antifungal prophylaxis; Minimal residual disease. María Argüello Marina, MAR Oncology and Hematology (2025) 5:08. Page 3 of 14 María Argüello Marina. (2025). Real-World Outcomes of FLT3 Inhibitors in Acute Myeloid Leukemia, a Multicenter Study. MAR Oncology and Hematology. (2025) 5:08 Background Acute myeloid leukemia (AML) is an aggressive hematologic malignancy characterized by the uncontrolled clonal proliferation of immature myeloid cells in the bone marrow, leading to suppressed normal hematopoiesis and peripheral tissue infiltration. AML is molecularly heterogeneous, exhibiting diverse clinical, morphological, and immunophenotypic features. It has a rapid onset, progressive course, and frequent resistance to chemotherapy [1,2]. With a median diagnosis age of 68, AML is the most common acute leukemia in adults, with a 5-year survival rate of approximately 30%, varying significantly by age group [2,3]. FLT3 gene mutations are common in AML and hold significant prognostic and therapeutic implications. FLT3 (FMS-like tyrosine kinase 3) encodes a receptor tyrosine kinase crucial for hematopoiesis. Activating mutations, such as internal tandem duplications (ITD) and tyrosine kinase domain (TKD) point mutations, are among the most frequent molecular abnormalities in AML [4,5]. FLT3 mutations occur in ~30% of AML cases at diagnosis, notably in 70% of patients with a normal karyotype and 35% of those with t(15;17), with a higher frequency in de novo AML (26%) than secondary AML (9%). These mutations correlate with hypercellularity, higher relapse rates, and are more common in women [6]. FLT3-ITD mutations are linked to poor AML prognosis, leading to leukocytosis, high blast cell percentages, greater treatment resistance, increased relapse risk, and reduced overall survival (OS) and progression-free survival (PFS) [6]. While FLT3-ITD AML patients can achieve complete remission with intensive chemotherapy, they have higher relapse rates and worse OS, particularly those with normal karyotype and intermediate cytogenetic risk [7,8]. In contrast, FLT3-TKD mutations have not demonstrated significant prognostic relevance despite multiple large-cohort studies [9–11]. Advances in genetic profiling have reshaped AML diagnostics, prognosis, and treatment strategies [2]. In 2022, an updated AML classification [12] and a new system [13] incorporated molecular findings into routine clinical practice, expanding recognized genetic abnormalities. Though FLT3 mutations are not considered AML-defining, they hold critical prognostic and therapeutic value. FLT3 inhibitors targeting the ATP-binding site of the tyrosine kinase domain have improved survival in FLT3+ AML [14,15]. The FDA has approved two FLT3 inhibitors: midostaurin and gilteritinib. Since 2019, the Spanish Hematology Treatment Program (PETHEMA) has recommended midostaurin with daunorubicin and cytarabine as first-line therapy for FLT3+ AML, to be administered from days +8 to +21 (or up to day 24 if induction extends to day 11). Midostaurin should not be initiated beyond this window. During consolidation with high-dose cytarabine, midostaurin is continued uninterrupted. It is also recommended during maintenance for patients post-consolidation (high-dose Ara-C or autologous transplant) for 12 cycles of 28 days but not after allogeneic transplantation. There is no survival benefit in adding midostaurin in consolidation if omitted during induction [16]. Gilteritinib is indicated as monotherapy for relapsed/refractory FLT3+ AML [16]. María Argüello Marina, MAR Oncology and Hematology (2025) 5:08. Page 4 of 14 María Argüello Marina. (2025). Real-World Outcomes of FLT3 Inhibitors in Acute Myeloid Leukemia, a Multicenter Study. MAR Oncology and Hematology. (2025) 5:08 FLT3+ AML and antifungal prophylaxis pose challenges due to a high risk of invasive fungal infections (IFI). During AML induction, posaconazole prophylaxis is standard due to severe prolonged neutropenia from intensive chemotherapy [16]. IFI incidence in FLT3-mutated AML patients is 10.5% (probable/proven) and 9.7% (possible) during induction, decreasing to 2.4% and 1.8% in consolidation [17]. Both midostaurin and gilteritinib are metabolized via CYP3A, which is inhibited by azoles like voriconazole, itraconazole, and posaconazole, increasing FLT3 inhibitor plasma levels [18]. PETHEMA advises avoiding CYP3A inducers and allows midostaurin dose adjustment to 50% (25 mg every 12 hours) if posaconazole or voriconazole prophylaxis is initiated during induction or consolidation [16]. This study evaluates real-world outcomes of FLT3 inhibitor therapy in FLT3+ AML, focusing on efficacy, safety, and the impact of antifungal prophylaxis. Materials and Methods Study Design This retrospective multicenter study was conducted across four Spanish hospitals: University Hospital of Guadalajara, University Hospital of Getafe, University Hospital Príncipe de Asturias, and University Hospital Infanta Leonor. Ethical approval was obtained from the respective Ethics Committees. Patients aged ≥18 years diagnosed with FLT3+ AML between January 2019 and March 2024 were included. Study Population Fifteen patients were enrolled, with their demographic and clinical characteristics summarized in Table 1. Table 1. Baseline Characteristics of the Study Population Variable N (%) Age 53 años (rango 31 – 76). Women 6 (40) Type of AML De novo 13 (87) Secondary 2 (13) FLT3 mutation ITD 11 (73) TKD 4 (27) María Argüello Marina, MAR Oncology and Hematology (2025) 5:08. Page 5 of 14 María Argüello Marina. (2025). Real-World Outcomes of FLT3 Inhibitors in Acute Myeloid Leukemia, a Multicenter Study. MAR Oncology and Hematology. (2025) 5:08 NPM1 mutated No 4 (33) Yes 11 (60) Karyotype Normal 12 (80) Altered 1 (7) Not performed 2 (13) ELN 2022 Risk Classification Low 1 (7) Intermediate 11 (73) High 3 (20) In the patient with an altered karyotype, t(8;21) and del(9)(q21q32) were identified, with t(8;21) classified as favorable risk despite coexisting with an FLT3 mutation. Among patients with high-risk AML, the key determinants were:  RUNX1 and ASXL1 mutations in one patient.  RUNX1 mutation in the second patient.  RUNX1 and TP53 mutations in the third patient. Data Collection Data were extracted from electronic medical records, including demographic variables, disease characteristics, and treatment outcomes. Statistical Analysis Descriptive statistics were applied. Qualitative variables are presented as frequencies and percentages, while quantitative variables are summarized by mean, median, and range. Results Descriptive Analysis of FLT3 Inhibitor Treatment All patients received midostaurin (50 mg every 12 hours) during induction, in combination with intensive 3+7 chemotherapy (Idarubicin 12 mg/m²/day IV on days 1–3 and Cytarabine 200 mg/m²/day IV as a continuous infusion on days 1–7). However, the two patients diagnosed with secondary AML received midostaurin in combination with VYXEOS. The time from diagnosis to FLT3 mutation result and subsequent initiation of FLT3 inhibitor therapy is María Argüello Marina, MAR Oncology and Hematology (2025) 5:08. Page 6 of 14 María Argüello Marina. (2025). Real-World Outcomes of FLT3 Inhibitors in Acute Myeloid Leukemia, a Multicenter Study. MAR Oncology and Hematology. (2025) 5:08 summarized in Table 2. Table 2. Timing of FLT3 Mutation Diagnosis and Targeted Treatment Initiation Patient Time to FLT3 Mutation Result from Date of Request (days) Time to start of FLT3 Inhibitor treatment from FLT3 Mutation Result (days) Time to start of FLT3 Inhibitor from Date of Diagnosis (days). 1 4 5 9 2 9 1 10 3 7 1 8 4 5 1 6 5 8 7 15 6 21 20 41 7 9 0 9 8 41 0 41 9 14 24 38 10 13 44 58 11 3 4 7 12 32 20 52 13 8 1 9 14 17 38 55 15 9 1 10 FLT3 mutation analysis was requested for all patients at the time of bone marrow biopsy upon diagnosis. The mean turnaround time for FLT3 mutation results was 13.3 days. Treatment initiation occurred a mean of 11.3 days after receiving FLT3 results, with FLT3 inhibitor therapy commencing a mean of 24.5 days postdiagnosis. Adverse Effects During midostaurin treatment, 9 of 15 patients (60%) experienced adverse effects (Table 3), with QT interval prolongation and diarrhea being the most frequent (33% each). Treatment was suspended in 4 patients (44%): two due to QT interval prolongation, one for liver function abnormalities, and one for enteritis. Among them, two (67%) resumed treatment at a reduced dose (25 mg every 12 hours). Patient 5 succumbed to intestinal obstruction. Additionally, Patient 1, who developed QT interval prolongation, required a dose reduction to 25 mg every 12 hours but did not necessitate treatment suspension. María Argüello Marina, MAR Oncology and Hematology (2025) 5:08. Page 7 of 14 María Argüello Marina. (2025). Real-World Outcomes of FLT3 Inhibitors in Acute Myeloid Leukemia, a Multicenter Study. MAR Oncology and Hematology. (2025) 5:08 Table 3. Adverse effects and treatment evolution with midostaurin Antifungal prophylaxis prescription Among the 15 patients, 9 (60%) received antifungal prophylaxis during chemotherapy induction, while 6 (40%) did not. All 9 patients who received midostaurin during induction also received antifungal prophylaxis: 5 with posaconazole (62.5%), 3 with micafungin (37.5%), and 1 with fluconazole (12.5%). No significant differences were observed in adverse effects or treatment suspension rates between patients receiving posaconazole and those on antifungals with lower CYP3A4 inhibition. Response to induction and consolidation Following induction, 12 patients (80%) achieved complete remission (CR), including 7 of 9 (78%) treated with midostaurin. Of these 12, 10 (83%) attained minimal residual disease (MRD) negativity. Seven patients (58%) proceeded to allogeneic stem cell transplantation (allo-SCT), while 5 (42%) underwent consolidation with high-dose Ara-C and midostaurin. One patient (Patient 5) died before reevaluation, one (Patient 8) was refractory, and another (Patient 15) achieved partial response (PR) but progressed before allo-SCT. Among the 8 patients who received midostaurin and were reevaluated, 5 (62.5%) achieved CR with MRD negativity, 2 (25%) achieved CR with MRD positivity, and 1 (12.5%) remained refractory. Detailed reevaluation and consolidation outcomes are summarized in Table 4. Patient Adverse Effect Required Treatment Suspension Treatment Resumed (Dose) 1 QT interval prolongation No 2 Diarrhea No 3 Liver profile alteration and abdominal pain Yes No 4 Diarrhea and moderate thrombocytopenia No 5 Enteritis Yes Deceased 7 Diarrhea No 8 Severe thrombocytopenia No 13 QT interval prolongation Yes Yes (25 mg/12h) 14 QT interval prolongation Yes Yes (25 mg/12h) María Argüello Marina, MAR Oncology and Hematology (2025) 5:08. Page 8 of 14 María Argüello Marina. (2025). Real-World Outcomes of FLT3 Inhibitors in Acute Myeloid Leukemia, a Multicenter Study. MAR Oncology and Hematology. (2025) 5:08 Table 4. Reevaluation and Consolidation Therapy EMR: Minimal Residual Disease; CR: Complete Remission; PR: Partial Remission; Allo-SCT: Allogeneic Stem Cell Transplantation. Follow-up The median follow-up duration for patients in this study was 6 months (range: 1–48 months). Among the 12 patients who responded to induction therapy and completed consolidation, 7 remain in complete remission, while 4 died during follow-up. One patient is currently undergoing allogeneic stem cell transplantation (alloSCT). Detailed follow-up data for each patient are presented in Table 5. Patient Response after Induction MRD after Induction Consolidation Therapy 1 CR Negative Allo-SCT 2 CR Negative Ara-C + midostaurin 3 CR Positive Allo-SCT 4 CR Negative Ara-C + midostaurin 5 Death Death Death 6 CR Negative Allo-SCT 7 CR Negative Allo-SCT 8 Refractory Positive Second-line treatment 9 CR Negative Ara-C + midostaurin 10 CR Negative Ara-C + midostaurin 11 CR Negative Allo-SCT 12 CR Negative Allo-SCT 13 CR Positive Ara-C + midostaurin 14 CR Negative Allo-SCT 15 PR Positive Progression, Second-line treatment María Argüello Marina, MAR Oncology and Hematology (2025) 5:08. Page 9 of 14 María Argüello Marina. (2025). Real-World Outcomes of FLT3 Inhibitors in Acute Myeloid Leukemia, a Multicenter Study. MAR Oncology and Hematology. (2025) 5:08 Table 5. Post-Consolidation Therapy Follow-up Patient Consolidation Therapy Current Status Follow-up Time (months) 1 Allo-SCT CR 11 2 Ara-C + midostaurin CR 3 3 Allo-SCT Death 6 4 Ara-C + midostaurin Death 2 5 Death Death 1 6 Allo-SCT CR 37 7 Allo-SCT CR 14 8 NA Death 7 9 Ara-C + midostaurin CR 49 10 Ara-C + midostaurin CR 37 11 Allo-SCT Allo-SCT 5 12 Allo-SCT CR 6 13 Ara-C + midostaurin Death 9 14 Allo-SCT Death 11 15 NA Death 5 Allo-SCT: Allogeneic hematopoietic stem cell transplantation, CR: Complete Remision, Discussion This study confirms that midostaurin's clinical benefits and tolerability, as observed in clinical trials, are reproducible in real-world settings, even in small patient cohorts. Notably, antifungal prophylaxis choice did not significantly affect tolerability or necessitate treatment discontinuation. Study Limitations As a retrospective descriptive study with a limited sample size, the generalizability of our findings is constrained. Additionally, the study lacks the ability to perform advanced statistical analyses or fully control for confounding variables. Descriptive retrospective studies primarily identify patterns within a population at a given time and cannot establish causal relationships.