This study conducted a multicenter prospective observational analysis using data from the Thai Acute Leukemia Working Group (TALWG) registry, covering the period from January 1, 2016, to December 31, 2023. The study included adult patients aged ≥ 18 years with newly diagnosed AML and available FLT3-ITD status. The clinical characteristics, cytogenetics, mutational status, risk stratification based on the European Leukemia Net (ELN) 2022 AML risk classification (4), treatment regimens (according to guideline for diagnosis and management of adult acute leukemia on behalf of the Thai Society of Hematology) (16), response rates, percentage of allogeneic stem cell transplantation, and survival outcomes, including relapse-free survival (RFS) and overall survival (OS), were collected and analyzed. RFS was defined as the time from AML diagnosis to relapse and OS was defined as the time from diagnosis to death from any cause. Patients with acute promyelocytic leukemia (APL), mixed phenotypic acute leukemia (MPAL), or lacking clinical information including FLT3 mutational status and survival outcomes were excluded from the study. FLT3-ITD detection techniques vary across institutions, including polymerase chain reaction (PCR) based on capillary electrophoresis and next-generation sequencing (NGS) of myeloid panels. NGS was used to determine other genetic mutation testing for AML risk classification. High-intensity treatment consisted of standard induction chemotherapy using the 7 + 3 regimen, which included a seven-day continuous intravenous infusion of cytarabine at 100 mg/m² over 24 h, combined with a three-day bolus of idarubicin at 12 mg/m². Alternatively, a modified 5 + 2 regimen was used (17), consisting of a five-day continuous infusion of cytarabine at 100 mg/m² over 24 hours and a two-day bolus of idarubicin at 12 mg/m². This was followed by 3–4 cycles of consolidation chemotherapy, involving intermediate-dose cytarabine (IDAC) at 1.5 g/m² or high-dose cytarabine (HiDAC) at 3 g/m², administered intravenously every 12 hours for three days. Low-intensity treatment included hypomethylating agents, such as a seven-day course of subcutaneous azacitidine at 75 mg/m², hydroxyurea, or transfusion support, as needed. Palliative care in this study was the only transfusion support as needed. Some AML patients with relapsed or refractory disease may receive salvage treatment with MEC (a five-day regimen consisting of intravenous Mitoxantrone 8 mg/m², Etoposide 100 mg/m², and Cytarabine 1 g/m²) or FLAG-Idarubicin (Fludarabine 30 mg/m² and Cytarabine 2 g/m² intravenously for five days, along with Idarubicin 8 mg/m² intravenously for three days, and G-CSF).

The primary endpoint of this study was the prevalence of the FLT3-ITD mutation in adult patients with AML in Thailand. The secondary endpoints included the clinical characteristics, treatment patterns, response rates, and survival outcomes of AML patients with and without the FLT3-ITD mutation in a real-world setting in Thailand.

Continuous variables are summarized using median values and range or interquartile range (IQR), while categorical variables are presented as percentages. The Chi-square test or Fisher’s exact test was used to compare categorical variables between FLT3-ITD AML and wild-type FLT3 AML patients, whereas the Mann-Whitney U test was used for continuous variables. Survival analysis was performed using the Kaplan-Meier method with the log-rank test to determine differences between groups. The Cox proportional hazard model was used to evaluate the hazard ratio (HR) with 95% confidence interval (95% CI) in the time-to-event analysis of the survival outcomes for univariable analyses (p-value <0.1 were included in the multivariable analyses. The sample size calculation was based on the primary outcome of the expected prevalence of the FLT3-ITD mutation in adult AML patients, which was estimated at 30% (1). A sample size of 360 patients was required to achieve a margin of error of 5% in estimating the prevalence with a 95% CI, accounting for a potential 10% loss. With this sample size, the anticipated 95% CI was 25-35% (18).

A total of 360 adult patients with newly diagnosed AML were included in this study. FLT3-ITD detection methods consisted of PCR in 140 cases (38.9%) and NGS in 220 cases (61.1%). Among these, 101 patients (28.1%) had FLT3-ITD mutations, whereas 259 patients (71.9%) had wild-type FLT3. The median age of patients with FLT3-ITD AML was 52 years (IQR 41-59) of compared to 51 years (IQR 36-61) for those with wild-type FLT3 AML (p=0.247). The proportion of male patients was similar between the FLT3-ITD (41.5%) and wild-type FLT3 (48.3%) groups (p=0.254). Regarding the Eastern Cooperative Oncology (ECOG) performance status, a higher proportion of patients with FLT3-ITD AML had an ECOG score of 3–4 compared than those with wild-type FLT3 AML (6.9% vs. 1.9%, p=0.018). Other baseline characteristics, such as the AML subtype, showed no significant differences between the two groups. Patients with FLT3-ITD AML had significantly higher median white blood cell counts (44.5 x 10⁹/L, IQR 12.0-110.1) compared to those with wild-type FLT3 AML (23.5 x 10⁹/L, IQR 7.1-62.1) (p=0.002). The median bone marrow blast percentage was also higher in the FLT3-ITD group (85%, IQR 68.7-90.0) compared than in the wild-type FLT3 group (80%, IQR 50.0-90.0) (p=0.011). Normal cytogenetics was more prevalent in the FLT3-ITD group (69.3%) than in the wild-type FLT3 group (52.1%) (p=0.003). There were significant differences in the distribution of certain mutations between the two groups. The FLT3-ITD group had a higher prevalence of NPM1 mutations (45.6% vs. 12.3%, p<0.001) and a lower incidence of biallelic CEBPA mutations (0 vs. 8.5%, p=0.043) ( Table 1 ). There were two types of NPM1 mutations: type A (c.863_864insTCTG) was found in 71.7% and 65.6% of FLT3-ITD and wild-type FLT3 while type B (c.863_864insCATG) was found in 28.3% of FLT3-ITD and 34.4% of wild-type FLT3 AML.

Treatment intensity was guided by physician discretion, largely based on age and performance status. Patients receiving high-intensity therapy were significantly younger (median age: 44 years; IQR 32–54) than those receiving low-intensity therapy (median age: 65 years; IQR 59–70) (p < 0.001). The proportion of patients with ECOG performance status 0–2 was higher in the high-intensity group (98.9%) compared to the low-intensity group (90.9%) (p = 0.001). Among FLT3-ITD patients, 69.3% received high-intensity induction chemotherapy, resulting in a complete remission (CR) rate of 55.7%. In the wild-type FLT3 group, 73.8% received high-intensity therapy, with a CR rate of 66.5%. These differences were not statistically significant (p = 0.397 and p = 0.109, respectively). Primary refractory disease occurred in 27.1% of FLT3-ITD patients and 16.7% of wild-type patients (p = 0.061). Among those receiving low-intensity regimens, non-response was common: 74.2% in FLT3-ITD and 60.3% in wild-type FLT3 (p = 0.180). In this study consisted of 45 patients who underwent allogeneic stem cell transplantation in the real-world data setting in Thailand. Of these, 26 patients (57.8%) received upfront allogeneic stem cell transplantation after first complete remission (CR1) while 19 patients (42.2%) underwent transplantation after achieving second complete remission (CR2) salvage therapy for relapse or refractory disease. Among those transplanted in CR1, there were 5 patients with FLT3-ITD AML and 21 with wild-type FLT3 AML. For those transplanted in CR2, 9 patients had FLT3-ITD AML and 10 had wild-type FLT3 AML.

Median follow-up was shorter in FLT3-ITD patients (8.1 months, IQR 3.4–14.8) than in wild-type FLT3 patients (11.4 months, IQR 4.6–21.5) (p = 0.006). Overall survival (OS) was significantly lower in FLT3-ITD patients (median 8.8 months) compared to wild-type FLT3 (13.2 months, log-rank test p < 0.001) ( Table 2 , Figure 1A ). When stratified by treatment intensity, the median OS in the high-intensity treatment group was 10.8 months for FLT3-ITD and 15.5 months for wild-type FLT3 patients (p = 0.002). In the low-intensity group, the median OS was 4.1 months for FLT3-ITD and 5.9 months for wild-type FLT3 patients (p = 0.169). In both mutational groups, high-intensity therapy resulted in significantly longer OS than low-intensity treatment (p < 0.001 for each comparison) ( Figure 1B ). When analyzed by age, a significant OS difference was observed among patients aged 30–60 years, with median OS of 13.9 months in wild-type FLT3 compared to 8.1 months in FLT3-ITD (p = 0.001) ( Figure 1C ). Among patients who underwent allogeneic stem cell transplantation, OS was longer in the wild-type FLT3 group than in the FLT3-ITD group (21.5 vs. 14.7 months, p < 0.001). Transplantation was associated with significantly improved OS in both subgroups: in FLT3-ITD patients, median OS was 14.7 months with transplantation versus 7.8 months without (p < 0.001); in wild-type FLT3 patients, the corresponding OS was 21.5 vs. 12.0 months (p < 0.001) ( Figure 1D ).

Relapse occurred in 117 patients (32.5%): 35.6% in FLT3-ITD and 31.3% in wild-type FLT3 (p = 0.132). Median relapse-free survival (RFS) was comparable between the two groups: 7.3 months for FLT3-ITD and 7.8 months for wild-type FLT3 (log-rank test, p = 0.704) ( Figure 2A ). When stratified by treatment intensity, RFS was 7.4 months in FLT3-ITD and 7.6 months in wild-type FLT3 among patients receiving high-intensity therapy (p = 0.764), and 5.2 months versus 7.8 months, respectively, among those receiving low-intensity treatment (p = 0.717). No significant differences in RFS were observed within each intensity group ( Figure 2B ). In the subgroup of patients aged over 60 years, FLT3-ITD AML was associated with significantly shorter RFS compared to wild-type FLT3 (5.2 vs. 7.8 months, p = 0.033) ( Figure 2C ). Among patients who underwent allogeneic stem cell transplantation, wild-type FLT3 patients had a significantly longer median RFS than those with FLT3-ITD (10.3 vs. 5.6 months, p = 0.013). However, when assessed within each mutational subgroup, the impact of transplantation on RFS did not reach statistical significance ( Figure 2D ).

Subgroup analyses showed that FLT3-ITD conferred a significantly higher risk of death across all age groups ( Figure 3A ). ECOG 3–4 was associated with a worse prognosis (HR 2.71, 95% CI: 1.25–5.87), as was secondary AML (HR 1.59, 95% CI: 1.17–2.18) and 11q23 rearrangement (HR 1.97, 95% CI: 0.97–4.02). Favorable outcomes were observed in patients with co-mutated NPM1 (HR 0.69, 95% CI: 0.53–0.90), while TP53 mutations trended toward poorer OS (HR 1.97, 95% CI: 0.87–4.46). For RFS, complex cytogenetics (HR 2.77, 95% CI: 1.37–3.59) and adverse ELN risk (HR 2.01, 95% CI: 1.23–3.28) were associated with increased relapse risk ( Figure 3B ). Multivariable analysis was only performed for OS because the p-value for RFS did not meet the criteria (p-value <0.1) for all parameters. Multivariable analysis confirmed worse OS with FLT3-ITD (HR 1.51), ECOG 3–4 (HR 2.47), and age >60 years (HR 1.89), while better OS with age <30 (HR 0.45), age 30–60 (HR 0.56), and ELN favorable-risk classification (HR 0.66).

Two patients with newly diagnosed FLT3-ITD AML received midostaurin in combination with intensive chemotherapy as frontline therapy. Both were classified as intermediate-risk AML with normal cytogenetics and concurrent type A NPM1 mutations. The first patient, a 27-year-old woman, was treated with a 7 + 3 induction regimen plus midostaurin, followed by four cycles of high-dose cytarabine (HiDAC) combined with midostaurin. She remained in complete remission on midostaurin maintenance after 11.1 months of follow-up. The second patient, a 52-year-old man, also received 7 + 3 plus midostaurin and achieved CR. He proceeded to consolidation with a single cycle of HiDAC and underwent allogeneic transplantation from a matched unrelated donor. Midostaurin maintenance was not continued post-transplant due to financial constraints. At 13.6 months of follow-up, he remained in remission. These two cases represent the only instances in this cohort where FLT3-targeted therapy was incorporated into first-line treatment.

Among 232 patients (64.4%) with relapsed or refractory AML, 77.2% of FLT3-ITD and 59.5% of wild-type FLT3 patients had relapsed or failed initial therapy. FLT3-ITD mutations were redetected at relapse in all previously mutated patients and newly emerged in 58.2% of initially wild-type cases. Only 21.5% of relapsed/refractory patients received salvage chemotherapy. MEC was administered to 13 FLT3-ITD and 25 wild-type patients, yielding CR rates of 23.1% and 32.0%, respectively (p = 0.425). FLAG-Idarubicin achieved CR in 1/5 FLT3-ITD (20.0%) and 3/7 wild-type FLT3 (42.9%) (p = 0.092). Notably, FLT3 inhibitors were not administered in the relapsed/refractory setting.