Citations

DNA double-strand breaks (DSBs) that occur during mitosis are primarily repaired by Polθ-mediated microhomology-mediated end joining (MMEJ). The CIP2A–TOPBP1 complex has been shown to tether broken chromatin at mitotic DSBs, but whether it coordinates with or functions independently of Polθ remains unknown. Here, we show that the CIP2A–TOPBP1 complex is recruited to mitotic DSB sites, where it directly interacts with Polθ and corecruits Polθ to chromatin. CIP2A sustains Polθ phosphorylation by inhibiting PP2A, thereby prolonging Polθ chromatin retention and enabling efficient repair. Upon repair completion, the CIP2A–TOPBP1 complex dissociates, PP2A dephosphorylates Polθ, and Polθ is released from chromatin. Loss of CIP2A impairs tumor growth, while disruption of CIP2A–Polθ binding leads to persistent DNA damage, micronucleus formation, and synthetic lethality in BRCA1/2-deficient cells. These findings uncover a cooperative mechanism by which CIP2A–TOPBP1 dynamically regulates Polθ in mitotic DSB repair and provide insights into the synthetic lethal interaction of CIP2A with BRCA1/2 under radiotherapy.

BMT CTN 1506 ("MORPHO") was a phase 3 study of post-hematopoietic cell transplantation (HCT) maintenance with gilteritinib versus placebo for patients with FLT3-ITD-mutated acute myeloid leukemia (AML) in first remission. Subgroup analysis indicated a significant benefit of post-HCT gilteritinib for participants in North America, but no benefit for those in Europe or Asia. We conducted a post-hoc analysis of the data focusing on days from AML diagnosis to HCT, pre-HCT FLT3 inhibitor use, and FLT3-ITD measurable residual disease (MRD). Participants transplanted < 120 days from AML diagnosis and/or those treated with FLT3 inhibition pre-HCT were more likely to have improved survival from post-HCT gilteritinib. Pre-HCT MRD levels were higher (P = 0.001) in participants transplanted within 120 days from diagnosis and in those treated with a FLT3 inhibitor pre-HCT and transplanted within 120 days (P = 0.008). Pre-HCT MRD was dependent on both FLT3 inhibitor use and time to HCT, as participants treated with successive courses of chemotherapy + FLT3 inhibition had successively lower MRD by the time of HCT. Time from AML diagnosis to HCT and pre-HCT FLT3 inhibitor use both appeared to impact MRD levels immediately prior to HCT, and geographic differences in these two practice patterns likely accounted for the observed regional differences in benefit from post-HCT gilteritinib. Increasing the number of courses of treatment pre-HCT may lower MRD sufficiently to eliminate the need for post-HCT inhibition, but with a presumed risk of some patients experiencing early progression. This trial was registered at www.clinicaltrials.gov as #NCT02997202.

Abstract Cholesterol has long been viewed as a structural component of cellular membranes, yet its role in DNA damage response remains poorly defined. Here, we show that ionizing radiation (IR) induces broad transcriptional upregulation of cholesterol biosynthesis, transport, and storage pathways, leading to sustained intracellular accumulation of cholesterol. BODIPY-cholesterol imaging, Filipin III staining, and quantitative subcellular fractionation confirmed selective nuclear enrichment of cholesterol following IR, coinciding with extensive chromatin remodeling. Proteomic profiling of cholesterol-interacting proteins revealed a strong enrichment of chromatin-associated factors, suggesting a previously unrecognized lipid-chromatin interface in irradiated cells. Functionally, cholesterol accumulation promoted chromatin compaction and repressive histone modification patterns, impairing DNA damage sensing and checkpoint activation despite increased underlying DNA lesions. These alterations facilitated aberrant mitotic entry, formation of cytoplasmic chromatin fragments (CCFs), and activation of cGAS-STING-NF-κB signaling. Cholesterol exposure ultimately diverted damaged cells toward a senescent fate, marked by Lamin B1 loss, p21 induction, and a robust senescence-associated secretory phenotype (SASP) enriched for IL-1 and TNF family cytokines. In vivo, dietary cholesterol exacerbated radiation-induced inflammation and weakened systemic anti-tumor immunity. Transcriptomic analyses of immunotherapy-treated patients revealed that tumors enriched for cholesterol import and senescence signatures were associated with poor response to PD-L1 blockade and worse survival. Together, these findings identify a cholesterol-chromatin-senescence axis that links metabolic remodeling to defective DNA damage signaling and immune suppression after radiation, highlighting cholesterol metabolism as a potential therapeutic vulnerability in cancer therapy. Citation Format: Yiqun Han, Yaobin Ouyang, Shouhai Zhu, Hangcheng Xu, Bin Chen, Ping Yin, Qin Zhou, Jinzhou Huang, Kuntian Luo, Zheming Wu, Huaping Xiao, Xinyi Tu, Jake A. Kloeber, Jiajun Jing, Xiaofeng Huang, Meng Xu Welliver, Zhenkun Lou, Robert Mutter. Cholesterol triggers chromatin stress to drive senescence and inflammation [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2026; Part 1 (Regular Abstracts); 2026 Apr 17-22; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2026;86(7 Suppl):Abstract nr 539.

Abstract Background Acute graft-versus-host disease (GVHD) is a major cause of non-relapse mortality (NRM) after allogeneic hematopoietic cell transplantation (HCT). High-dose steroids are standard first-line therapy for grade II–IV acute GVHD, whereas systemic treatment (tx) is generally not recommended for grade I. However, in practice many patients (pts) with grade I GVHD receive systemic steroids. A prior GITMO randomized trial (n=173) of grade I GVHD to either systemic steroid tx or “watch and wait” found that preemptive steroid tx reduced progression to grade II but not grade III/IV GVHD, increased serious infections, and resulted in similar chronic GVHD, NRM and survival (Bacigalupo, Haematologica 2017). In this study we analyzed real world evidence for early systemic steroid use and the potential impact of serum biomarkers in grade I GVHD. Methods We analyzed clinical data and serum samples from pts with grade I acute GVHD at 24 Mount Sinai Acute GVHD International Consortium (MAGIC) centers between 2014 and 2022 who were treated according to physician discretion. Pts were divided into a preemptive steroid tx group or a watch-and-wait group (systemic steroids administered only if progression to grade II–IV GVHD). Preemptive steroid use was treated as a time-dependent covariate and a frailty proportional hazards model with random effects was used to adjust for center effects to account for possible heterogeneity in clinical practices across transplant centers. Serum samples collected at the diagnosis of grade I GVHD were analyzed for ST2 and REG3α to calculate validated Ann Arbor (AA) scores (1, 2, 3). Results Grade I GVHD was diagnosed in 1143 pts; 591 (52%) received preemptive tx and 552 (48%) were treated by a watch-and-wait strategy. In the preemptive tx group, steroids were initiated at a median of 0 days and within 7 days for >90%. The median initial dose of steroids was 1 mg/kg of prednisone or its equivalent. In the watch and wait group, only 184 pts (33%) required systemic steroids for progression to grade II-IV GVHD at a median of 14 days from grade I diagnosis. Preemptive steroid tx reduced the risk of grade II–IV acute GVHD (HR, 0.71; 95% CI, 0.56–0.89; P=0.003), but not the risk of grade III/IV acute GVHD (HR, 1.03; 95% CI, 0.69–1.52; P=0.899) or chronic GVHD (HR, 1.03; 95% CI, 0.69–1.52; P=0.899), consistent with the GITMO trial. The 12-month incidence of NRM was higher for preemptive tx vs. watch and wait (13% vs 7%, P=0.002). In multivariate analysis preemptive steroid use independently predicted an increased risk of NRM (HR, 1.63; 95% CI, 1.06–2.50; P=0.026) as did several other known risk factors (older recipient age, umbilical cord blood donor, HCT-CI ≥3, and myeloablative conditioning). Greater NRM in the preemptive tx group was driven primarily by 3-fold more infectious deaths; deaths due to uncontrolled GVHD were similar for both tx groups. The risk for relapse was unexpectedly lower in the preemptive tx group (HR 0.64; 95% CI 0.47-0.88; P=0.006) and overall survival was therefore not different between groups, but risk factors for relapse such as minimal residual disease status were not available precluding further analysis of this finding. Serum was collected in 871 (76%) pts at onset of grade I GVHD for retrospective biomarker analysis. AA scores were AA1 (80%), AA2 (15%), and AA3 (5%). AA scores were highly predictive of progression to grade III/IV GVHD (AA1 vs AA2 vs AA3: 9% vs 14% vs 44%, all P<0.001) and the risk of 12-month NRM (8% vs 16% vs 39%, all P<0.001); this pattern was observed in both tx groups. The negative effect of preemptive steroid tx was most pronounced in pts with grade I/AA1 GVHD who experienced 5-fold more infectious related deaths compared to pts managed with a watch and wait approach. Conclusion Treatment of grade I GVHD with systemic steroids did not reduce the incidence of grade III/IV GVHD or deaths due to uncontrolled GVHD and instead increased the risk of NRM from infections compared to pts who were treated only after GVHD progressed. Importantly, 2/3 of the watch and wait pts never needed systemic steroid tx. These findings remained robust after adjusting for multiple confounders, including center effects, and were consistent with the GITMO trial. MAGIC biomarkers at the onset of grade I GVHD predicted outcomes and a watch and wait strategy may be best for the 80% of pts with AA1 GVHD. Better treatment options are needed for the 20% of pts with grade I and AA2/3 GVHD.

Abstract INTRODUCTION Allogeneic hematopoietic cell transplantation (alloHCT) is indicated in patients (pts) with FLT3-ITD mutated AML. The randomized BMT CTN 1506 trial (Levis et al. JCO) demonstrated that maintenance with FLT3 inhibitor gilteritinib (gilt) significantly improved relapse-free survival (RFS) among pts with detectable peri-alloHCT minimal residual disease (MRD) but was also associated with a greater degree of myelosuppression and infections. In older pts, aged >60 years, increasing post-HCT toxicity may adversely impact outcomes. On this basis, we performed a post-hoc analysis of pts aged > 60 years enrolled onto BMT CTN 1506 to examine the impact of gilteritinib maintenance in older pts. METHODS Pts ≥60 years randomized on BMT CTN 1506 (gilt=47, placebo=57; N=104) were included. The primary endpoint of this post-hoc analysis was RFS. We additionally assessed overall survival (OS), incidence of relapse, non-relapse mortality (NRM) in all pts and in pts with detectable MRD. RESULTS Baseline characteristics were balanced. Age was similar (65.2 vs 64.7 years; p = 0.12), as was prior TKI exposure, and NPM1 mutation status. Myeloablative conditioning (MAC) was used in 8 (17%) pts randomized to gilt and 18 (32%) pts randomized to placebo (p=0.08). Median f/u of survivors was 43.8 months (range:1-61 mo.). Estimated RFS and OS at 48 months were not different between groups (RFS: gilt: 57.0%, 95%CI 44.1-73.7%, placebo: 57.1%, 95%CI 45.4-71.8%; OS: gilt: 56.9%, 95%CI 42.9-46.7%, placebo: 58.4%, 95%CI 46.7-73.1%). While gilt assignment did not affect survival, several predictors of poorer survival were identified including use of reduced intensity conditioning (RIC) (HR = 3.46; p = 0.014), use of calcineurin inhibitor/MTX for graft-vs-host disease (GVHD) prophylaxis (HR = 2.29; p = 0.041), high-risk cytogenetics (HR = 2.64; p = 0.021), and MRD (+) pre-HCT (HR = 2.29; p = 0.018). Finally, relative to gilt assignment, opposing rates of relapse and NRM were observed. The incidence of relapse was lower with gilt (16%, 95%CI 6.8-28% vs 32%, 95%CI 20-45%, p=0.046) but NRM was higher (27%, 95%CI 15-41% vs 11%, 95% CI 4.3-21%, p=0.033). We next analyzed the 49 pts (gilt=22, placebo=27) with detectable peri-HCT MRD. RFS and OS again were not different (RFS: gilt: 44.4%, 95%CI 27.1-72.7%, placebo: 43.8%, 95%CI 28.4-67.5%, OS: gilt: 49.2%,95%CI, 31.3-77.4%, placebo: 55.6%, 95%CI 39.4-77.8%). The incidence of relapse trended lower in gilt pts (25%, 95%CI, 5.3-44.7% vs 45% (95%CI, 25-63%), p=0.2) while NRM trended higher (31%, 95%CI 12-52% vs 11%, 95%CI, 2.7-26%, p=0.12). Seventeen (36%) patients completed planned 2 year maintenance with gilt compared to 29 (51%) completing therapy with placebo. Median time on gilt was 13.2 months. The most common reason for discontinuation was adverse events (n=19, 40%), of which cytopenias (n=8) and infections (n=4) were most frequent. Non-relapse causes of death among gilt treated pts included infections (n=8), intracranial hemorrhage related to thrombocytopenia (n=1), second cancer (n=1), and Guillain-Barre syndrome (n=1). Most infections (n=5) were attributed to GVHD as an underlying cause. CONCLUSION Among pts aged ≥60 years, gilt maintenance did not improve RFS or OS. Gilt use was associated with reduced relapse regardless of peri-HCT MRD status demonstrating disease effect; however, higher NRM limited overall benefit. In older FLT3 mutated pts, employing strategies to mitigate HCT related toxicity, e.g. alternative GVHD prophylaxis strategies, may better accommodate use of maintenance therapy including gilt. Lower doses of gilt (particularly with azole co-use) may be worth exploring to mitigate drug AEs, improve compliance, thus further improving benefit.

Abstract Aims BMT CTN 1506 (“MORPHO”) was a global phase 3 study of post-hematopoietic cell transplantation (HCT) maintenance with gilteritinib versus placebo for patients with FLT3-ITD-mutated AML in CR1. The study did not meet its primary endpoint of improved relapse-free survival (RFS) for post-HCT gilteritinib, but subgroup analysis indicated a benefit for participants with pre-HCT measurable residual disease (MRD). Subgroup analysis also indicated a statistically significant benefit of post-HCT gilteritinib for participants in North America, but no benefit for those in Europe or Asia. RFS for the control arms in Europe and Asia was higher than anticipated, suggesting that participants with different disease biology may have accrued to the study in these different geographic regions. In the primary analysis of the study, pre-HCT FLT3 inhibitor use and MRD across the entire study population were both found to have impacted outcomes. Time from diagnosis to HCT, a reflection of local practice patterns, is also known to impact outcomes for FLT3-ITD AML. We hypothesized that local practice patterns of pre-HCT FLT3 inhibitor use and time from AML diagnosis to HCT could have influenced the disease biology of study pts at the time of enrollment. This would be predicted to result in pre-HCT MRD levels and could provide an explanation for the regional differences observed in the study outcome. Methods We conducted a post-hoc analysis of the data focusing on days from AML diagnosis to HCT, pre-HCT FLT3 inhibitor use, and FLT3-ITD MRD assessed by a high-sensitivity assay. Eligibility requirements included FLT3-ITD-mutated AML in first remission after intensive chemotherapy and HCT occurring within 12 months of achieving remission. Patients refractory to induction therapy, or those with a history of relapse, were ineligible. Results Accrual took place in 16 different countries, with 5 countries accounting for 79.7% of the total accrual: USA 42.7%; Japan 15.7%; Korea 8.4%; UK 6.7%; Germany 6.2%; other countries 20.2%. In two countries, USA and Germany (48.9% of total enrollment), participants underwent HCT a median of 119 days after AML diagnosis, and 90.2% were treated with a FLT3 inhibitor pre-HCT. In contrast, in Japan, Korea, the UK and the other 11 countries all combined, participants underwent HCT a median of 152.5 days after AML diagnosis, and only 30.8% received any FLT3 inhibitor pre-HCT. Amongst all participants, those transplanted < 120 days from AML diagnosis and/or those treated with FLT3 inhibition pre-HCT were more likely to have improved RFS from post-HCT gilteritinib. RFS was improved with post-HCT gilteritinib in the US and Germany (HR 0.397; CI 0.220-0.718), whereas no benefit was evident in all other countries combined (HR 1.184; CI 0.685-2.048). Pre-HCT MRD levels were significantly higher (P = 0.011) in participants transplanted within 120 days from diagnosis as well as in those treated with a FLT3 inhibitor pre-HCT and also transplanted within 120 days (P = 0.019). Pre-HCT MRD was dependent on both FLT3 inhibitor use and time to HCT, as participants treated with successive courses of chemotherapy + FLT3 inhibition had successively lower MRD by the time of HCT. Conclusions The time from AML diagnosis to HCT and FLT3 inhibitor use pre-HCT both appeared to impact MRD levels immediately prior to HCT, and geographic differences in these two practice patterns likely accounted for the regional differences in benefit from post-HCT gilteritinib observed in BMT CTN 1506. Successive courses of chemotherapy without FLT3 inhibition appears to have selected a more favorable risk (e.g., MRD-lower) population for enrollment. Successive courses of chemotherapy combined with FLT3 inhibition progressively eradicated MRD, such that a majority of participants undergoing HCT after 3 or 4 courses were MRD negative and therefore unlikely to benefit from post-HCT gilteritinib. These findings have implications for clinical practice. Increasing the number of courses of chemotherapy combined with FLT3 inhibition before HCT may lower MRD sufficiently to eliminate the need for post-HCT inhibition for some patients but, alternatively, the additional delay could increase the risk of pre-HCT relapse, preventing patients from receiving HCT in first remission.

Abstract Overall response (OR) that combines complete (CR) and partial responses (PR) is the conventional end point for acute graft-versus-host disease (GVHD) trials. Because PR includes heterogeneous clinical presentations, reclassifying PR could produce a better end point. Patients in the primary treatment cohort from the Japanese Society for Transplantation and Cellular Therapy (JSTCT) were randomly divided into training and validation sets. In the training set, a classification and regression tree algorithm generated day 28 refined response (RR) criteria based on symptoms at treatment and day 28. We then evaluated RR for primary and second-line treatments, using the area under the receiver operating characteristic curve (AUC) and negative predictive value (NPV) for 6-month nonrelapse mortality as performance measures. RR considered patients with grade 0/1 at day 28 without additional treatment as responders. RR for primary treatment produced higher AUCs than OR with small improvement of NPVs in both validation sets: JSTCT (AUC, 0.73 vs 0.69 [P < .001]; NPV, 92.0% vs 89.6% [P < .001]) and the Mount Sinai Acute GVHD International Consortium (MAGIC; AUC, 0.71 vs 0.68 [P = .032]; NPV, 90.9% vs 89.8% [P = .009]). RR for second-line treatment produced similar AUCs but much higher NPVs than OR in both validation sets of JSTCT (AUC, 0.64 vs 0.63 [P = .775]; NPV, 74.5% vs 66.0% [P < .001]) and MAGIC (AUC, 0.67 vs 0.64 [P = .105]; NPV, 86.8% vs 76.1% [P = .004]). Classifying persistent but mild skin symptoms as responses and residual lower gastrointestinal GVHD as nonresponses were major drivers in improving the prognostic performance of RR. Our externally validated day 28 RR would serve as a better end point than conventional criteria in future first- and second-line treatment trials.

Abstract We conducted a post hoc analysis of data from Blood and Marrow Transplant Clinical Trials Network 1506 (MORPHO), a randomized trial of gilteritinib vs placebo as posttransplantation maintenance for patients with FLT3-ITD–mutated acute myeloid leukemia (AML) undergoing allogeneic hematopoietic cell transplantation (HCT), focusing the interactions between conditioning regimen intensity, measurable residual disease (MRD), and NPM1 comutation status reported from diagnosis. Comparing FLT3-ITD MRD before and after conditioning, there was no difference between myeloablative conditioning (MAC) and reduced-intensity conditioning (RIC) in eradication or reduction of FLT3-ITD MRD. For participants who were FLT3-ITD MRD negative before HCT, there was no difference in the cumulative incidence of relapse during follow-up between those receiving MAC vs RIC. NPM1 comutation was associated with the largest magnitude of relapse-free survival benefit from post-HCT gilteritinib, and in these participants, post-HCT gilteritinib in the setting of RIC appeared to be as effective as MAC at preventing relapse. MAC appeared superior to RIC in preventing relapse only in participants who were NPM1 wild type at diagnosis and FLT3-ITD MRD positive before HCT. Our findings suggest that only a subset of patients with FLT3-ITD AML undergoing HCT may benefit from MAC and that, similar to AML therapy before HCT, the intensity of the HCT regimen should be adapted according to the molecular features of the disease. This trial was registered at www.clinicaltrials.gov as #NCT02997202.

Abstract Poly ADP ribose polymerase inhibitors (PARPi) are being investigated in combination with photon and proton radiotherapy in clinical trials of pediatric and adult malignancies. The precise mechanisms of PARPi radiosensitization, and whether differences in photon and proton-mediated relative efficacy exist, have not been fully elucidated. To study mechanisms of PARPi radiosensitization we investigated the effects of PARPi in combination with photons and two different ionizing densities of protons delivered at the entrance (ENT) or the Bragg peak (BP) of the profile (dose-averaged LET [LETd] 2.2 and 7.0 keV/µm, respectively) of a 76.8 MeV proton beam after observing an extreme tumor and normal tissue response in an 18-year-old female patient with high grade glioma treated veliparib and proton therapy in a Children’s Oncology Group clinical trial. BRCA1/2 wild-type hTERT RPE-1, U2OS, and MDA-MB-231 cells were hypersensitive to the combination of veliparib and proton BP, with enhanced relative biological effectiveness (RBE) at 2 Gy values of 1.7, 1.4, and 1.3, respectively. Similar findings were observed with talazoparib and olaparib, suggesting that PARP trapping efficiency was not a major influence on the proton BP RBE. Further, we did not observe differences in transcription replication conflict between the different proton ionizing densities. Unexpectedly, DNA fiber assays revealed more elongated replication fork tracks in PARPi treated cells 60 minutes after proton BP compared with proton ENT, indicative of accelerated replication fork progression. To assess gap formation in the vicinity of nascent DNA we treated cells with the ssDNA-specific S1 nuclease and found that the lengths of CldU-labeled tracks were significantly reduced in cells treated with the PARPi/proton BP combination, suggestive of greater gap formation at replication forks. We postulated that more ssDNA gaps were being converted to DSBs during replication as we further observed that PARPi/proton BP resulted in increased γH2AX foci at 4- and 24-hours after treatment. Consistent with increased DSB formation, a higher proportion of cells arrested in the G2/M phase of the cell cycle at 24 hours following PARPi/proton BP. Despite being arrested in G2/M when homologous recombination is active, there was a significant increase in 53BP1 and a decrease in RAD51 recruitment, indicative of upregulated repair by more error-prone non-homologous end-joining (NHEJ) repair pathway. The enhanced proton BP RBE in PARPi treated cells was abrogated upon knockdown of XRCC4, a critical component of NHEJ repair pathway, suggesting that toxic NHEJ may be contributing to the enhanced proton BP RBE. In conclusion, PARPi renders cells hypersensitive to high LET BP proton irradiation. Enhancing the LET in combination with PARPi warrants further investigation to overcome therapeutic resistance. Citation Format: Yiqun Han, Qin Zhou, Anna Olson, Cameron M. Callaghan, Bin Chen, Nicholas B. Remmes, Meng Xu Welliver, Zheming Wu, Daniel K. Ebner, Jake A. Kloeber, Zhenkun Lou, Robert W. Mutter. Poly ADP ribose polymerase inhibitors potentiate proton therapy end-of-range relative biological effective dose by increasing replication stress [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 4689.

Abstract BMT CTN (Blood and Marrow Transplant Clinical Trials Network) 1506 (“MORPHO”) was a randomized study of gilteritinib compared with placebo as maintenance therapy after hematopoietic cell transplantation (HCT) for patients with FLT3-ITD–mutated acute myeloid leukemia (AML). A key secondary end point was to determine the impact on survival of before and/or after HCT measurable residual disease (MRD), as determined using a highly sensitive assay for FLT3-ITD mutations. Generally, gilteritinib maintenance therapy was associated with improved relapse-free survival (RFS) for participants with detectable peri-HCT MRD, whereas no benefit was evident for those lacking detectable MRD. We conducted a post hoc analysis of the data and found that the level of MRD detected with this approach correlated remarkably with RFS and relapse risk, and that MRD detectable at any level negatively affected RFS. In the placebo arm, 42.2% of participants with detectable FLT3-ITD MRD relapsed compared with 13.4% of those without detectable MRD. We found that 14.8% of participants had multiple FLT3-ITD clones detected as MRD and had worse survival irrespective of treatment arm. Finally, we examined the kinetics of FLT3-ITD clonal relapse or eradication and found that participants on the placebo arm with detectable MRD relapsed rapidly after HCT, often within a few weeks. MRD-positive participants on the gilteritinib arm relapsed either with FLT3 wild-type clones (assessed by capillary electrophoresis), after cessation of gilteritinib with persistent MRD, or on progression of multiclonal disease. These data demonstrate the potential of FLT3-ITD MRD to guide therapy with gilteritinib for this subtype of AML. This trial was registered at www.clinicaltrials.gov as #NCT02997202.