Concomitant inhibition of the thioredoxin system and nonhomologous DNA repair potently sensitizes Philadelphia-positive lymphoid leukemia to tyrosine kinase inhibitors.

Breakpoint cluster region-Abelson (BCR::ABL1) gene fusion is an essential oncogene in both chronic myeloid leukemia (CML) and Philadelphia-positive (Ph+) B-cell acute lymphoblastic leukemia (B-ALL). While tyrosine kinase inhibitors (TKIs) are effective in up to 95% of CML patients, 50% of Ph+ B-ALL cases do not respond to treatment or relapse. This calls for new therapeutic approaches for Ph+ B-ALL. Previous studies have shown that inhibitors of the thioredoxin (TXN) system exert antileukemic activity against B-ALL cells, particularly in combination with other drugs. Here, we present that peroxiredoxin-1 (PRDX1), one of the enzymes of the TXN system, is upregulated in Ph+ lymphoid as compared to Ph+ myeloid cells. PRDX1 knockout negatively affects the viability of Ph+ B-ALL cells and sensitizes them to TKIs. Analysis of global gene expression changes in imatinib-treated, PRDX1-deficient cells revealed that the nonhomologous end-joining (NHEJ) DNA repair is a novel vulnerability of Ph+ B-ALL cells. Accordingly, PRDX1-deficient Ph+ B-ALL cells were susceptible to NHEJ inhibitors. Finally, we demonstrated the potent efficacy of a novel combination of TKIs, TXN inhibitors, and NHEJ inhibitors against Ph+ B-ALL cell lines and primary cells, which can be further investigated as a potential therapeutic approach for the treatment of Ph+ B-ALL.

Telomere loss is accompanied by decreased pool of shelterin proteins TRF2 and RAP1, elevated levels of TERRA and enhanced glycolysis in imatinib-resistant CML cells.

Telomere length may be maintained by telomerase nucleoprotein complex and shelterin complex, namely TRF1, TRF2, TIN2, TPP1, POT1 and RAP1 proteins and modulated by TERRA expression. Telomere loss is observed during progression of chronic myeloid leukemia (CML) from the chronic phase (CML-CP) to the blastic phase (CML-BP). The introduction of tyrosine kinase inhibitors (TKIs), such as imatinib (IM), has changed outcome for majority of patients, however, a number of patients treated with TKIs may develop drug resistance. The molecular mechanisms underlying this phenomenon are not fully understood and require further investigation. In the present study, we demonstrate that IM-resistant BCR::ABL1 gene-positive CML K-562 and MEG-A2 cells are characterized by decreased telomere length, lowered protein levels of TRF2 and RAP1 and increased expression of TERRA in comparison to corresponding IM-sensitive CML cells and BCR::ABL1 gene-negative HL-60 cells. Furthermore, enhanced activity of glycolytic pathway was observed in IM-resistant CML cells. A negative correlation between a telomere length and advanced glycation end products (AGE) was also revealed in CD34+ cells isolated from CML patients. In conclusion, we suggest that affected expression of shelterin complex proteins, namely TRF2 and RAP1, TERRA levels, and glucose consumption rate may promote telomere dysfunction in IM-resistant CML cells.

The interplay between telomeric complex members and BCR::ABL1 oncogenic tyrosine kinase in the maintenance of telomere length in chronic myeloid leukemia.

PURPOSE: Chronic myeloid leukemia (CML) is a myeloproliferative neoplasm characterized by recurrent genetic aberration in leukemic stem cells, namely Philadelphia chromosome caused by reciprocal translocation t(9;22)(q34;q11). In our study, we analyzed the telomeric complex expression and function in the molecular pathogenesis of CML. METHODS: We employed CD34+ primary leukemic cells, comprising both leukemic stem and progenitor cell populations, isolated from peripheral blood or bone marrow of CML patients in chronic and blastic phase to analyze the telomere length and telomeric-associated proteins. RESULTS: The reduction in telomere length during disease progression was correlated with increased expression of BCR::ABL1 transcript and the dynamic changes were neither associated with the enzymatic activity of telomerase nor with gene copy number and expression of telomerase subunits. Increased expression of BCR::ABL1 was positively correlated with expression of TRF2, RAP1, TPP1, DKC1, TNKS1, and TNKS2 genes. CONCLUSIONS: The dynamics of telomere length changes in CD34+ CML cells is dependent on the expression level of BCR::ABL, which promotes the expression of certain shelterins including RAP1 and TRF2, as well as TNKS, and TNKS2, and results in telomere shortening regardless of telomerase activity. Our results may allow better understanding of the mechanisms responsible for the genomic instability of leukemic cells and CML progression.

HRAS mutation positive multiple myeloma in the type 2 CALR mutation positive essential thrombocythemia: A case report.

Out of BCR-ABL negative myeloproliferative neoplasm (MPNPh- ) patients, 3%-14% display a concomitant monoclonal gammopathy of unknown significance (MGUS). In most cases, the diagnosis of plasma cell dyscrasia is either synchronous with that of MPNPh- or occurs later on. We present a 50-year-old patient with type 2 CALR Lys385Asnfs*47 mutation positive essential thrombocythemia (ET) who developed symptomatic multiple myeloma (MM) 13 years after the diagnosis of ET during PEG-INF2α treatment. The NGS study performed at the time of the MM diagnosis revealed the HRAS Val14Gly/c.41T〉G mutation and the wild type CALR, JAK2 and MPL gene sequence. In the presented case, the complete molecular remission of ET was achieved after 16 months of PEG-INF2α treatment. The origin of MM cells in MPNPh- patients remains unknown. Published data suggests that type 2 CALRins5 up-regulate the ATF6 chaperone targets in hematopoietic cells and activate the inositol-requiring enzyme 1α-X-box-binding protein 1 pathway of the unfolded protein response (UPR) system to drive malignancy. It cannot be excluded that endoplasmic reticulum stress induced by the increased ATF6 resulted in an abnormal redox homeostasis and proteostasis, which are factors linked to MM. The presented case history and the proposed mechanism of mutant CALR interaction with UPR and/or ATF6 should initiate the discussion about the possible impact of the mutant CALR protein on the function and genomic stability of different types of myeloid cells, including progenitor cells.

SARS-CoV-2 Infection in Patients Treated with Azacitidine and Venetoclax for Acute Leukemia: A Report of a Case Series Treated in a Single Institution.

INTRODUCTION: Venetoclax combined with azacitidine (AZA-VEN) constitutes an option for the treatment of acute myeloid leukemia. There are, however, no data on the COVID-19 incidence and outcome in patients treated with AZA-VEN. METHODS: Patients with acute leukemia treated with AZA-VEN at a single institution were included in this prospective observational study. RESULTS: Thirteen patients were enrolled, 46% with treatment-naïve, and 56% with relapsed/refractory disease. Fifty-four percent of patients were males; the median age was 69 years. Six patients (46%) developed COVID-19 during the observation time. The median time to COVID-19 was 24 days from the initiation of AZA-VEN. The 2-month cumulative incidence of COVID-19 was 46.2%. Two patients (33%) succumbed to COVID-19. The 100-day COVID-19-free survival from AZA-VEN initiation was 61%. The median follow-up time was 4.3 months. DISCUSSION/CONCLUSION: COVID-19 constitutes a frequent complication of AZA-VEN treatment in the era of the COVID-19 pandemic, leading to death in a significant proportion of patients.

FGFR2 point mutation in 2 cases of pleomorphic adenoma progressing to myoepithelial carcinoma.

Introduction: Salivary gland tumours are rare neoplasms. Pleomorphic adenoma (PA) is the most frequent benign lesion. Myoepithelial carcinoma (MECA) is rarely recognized malignancy, but the prognosis is unfavourable. The aim of this study was to identify genetic rearrangements that might be responsible for dynamic MECA progression in patients with primary radical PA excision. Material and methods: Next-generation sequencing (NGS) of 1500 gene coding sequences was performed in primary and recurrent tumour tissue collected from 2 patients, in whom PA was initially diagnosed and within one year multifocal MECA was detected. Formalin-fixed paraffin-embedded blocks with tumour tissues were subject to NGS analysis, involving small-scale mutations, as well as focal and chromosomal arm-level copy number changes. Results: This study showed mutations in the FGFR2 gene in PA and MECA tissues, obtained from both patients. One of them, pathogenic mutation p.Pro253Arg, was associated with sensitivity to registered drug inhibitors. Additionally, FGFR1, EGFR, and CDK4/CDK6 amplification, as well as CDKN2A/B deletion, were detected in one case. Furthermore, mutations in suppressor gene APC2 and PIK3C2A were detected, but only in MECA tissue. The analysis also identified the following chromosomal copy alterations: 4q12-q13.3, 9p21.3, 5q23.1-q34, del8p23.3-p12, and del13q21.31-q31.1. Conclusions: Rearrangement of the FGFR2 gene, identified in primary PA and MECA ex PA samples of both our patients, may be responsible for the malignant transformation and the disease progression. Further studies are encouraged to confirm the relevance of the findings. The therapy option with FGFR2 inhibitors may be considered in advanced or metastatic MECA ex PA with confirmed FGFR2 mutations.

Targeting integrated stress response with ISRIB combined with imatinib treatment attenuates RAS/RAF/MAPK and STAT5 signaling and eradicates chronic myeloid leukemia cells.

The integrated stress response (ISR) facilitates cellular adaptation to unfavorable conditions by reprogramming the cellular response. ISR activation was reported in neurological disorders and solid tumors; however, the function of ISR and its role as a possible therapeutic target in hematological malignancies still remain largely unexplored. Previously, we showed that the ISR is activated in chronic myeloid leukemia (CML) cells and correlates with blastic transformation and tyrosine kinase inhibitor (TKI) resistance. Moreover, the ISR was additionally activated in response to imatinib as a type of protective internal signaling. Here, we show that ISR inhibition combined with imatinib treatment sensitized and more effectively eradicated leukemic cells both in vitro and in vivo compared to treatment with single agents. The combined treatment specifically inhibited the STAT5 and RAS/RAF/MEK/ERK pathways, which are recognized as drivers of resistance. Mechanistically, this drug combination attenuated both interacting signaling networks, leading to BCR-ABL1- and ISR-dependent STAT5 activation. Consequently, leukemia engraftment in patient-derived xenograft mice bearing CD34+ TKI-resistant CML blasts carrying PTPN11 mutation responsible for hyperactivation of the RAS/RAF/MAPK and JAK/STAT5 pathways was decreased upon double treatment. This correlated with the downregulation of genes related to the RAS/RAF/MAPK, JAK/STAT5 and stress response pathways and was associated with lower expression of STAT5-target genes regulating proliferation, viability and the stress response. Collectively, these findings highlight the effect of imatinib plus ISRIB in the eradication of leukemic cells resistant to TKIs and suggest potential clinical benefits for leukemia patients with TKI resistance related to RAS/RAF/MAPK or STAT5 signaling. We propose that personalized treatment based on the genetic selection of patients carrying mutations that cause overactivation of the targeted pathways and therefore make their sensitivity to such treatment probable should be considered as a possible future direction in leukemia treatment.

Tracking Clonal Evolution of Multiple Myeloma Using Targeted Next-Generation DNA Sequencing.

Clonal evolution drives treatment failure in multiple myeloma (MM). Here, we used a custom 372-gene panel to track genetic changes occurring during MM progression at different stages of the disease. A tumor-only targeted next-generation DNA sequencing was performed on 69 samples sequentially collected from 30 MM patients. The MAPK/ERK pathway was mostly affected with KRAS mutated in 47% of patients. Acquisition and loss of mutations were observed in 63% and 37% of patients, respectively. Four different patterns of mutation evolution were found: branching-, mutation acquisition-, mutation loss- and a stable mutational pathway. Better response to anti-myeloma therapy was more frequently observed in patients who followed the mutation loss-compared to the mutation acquisition pathway. More than two-thirds of patients had druggable genes mutated (including cases of heavily pre-treated disease). Only 7% of patients had a stable copy number variants profile. Consequently, a redistribution in stages according to R-ISS between the first and paired samples (R-ISS″) was seen. The higher the R-ISS″, the higher the risk of MM progression and death. We provided new insights into the genetics of MM evolution, especially in heavily pre-treated patients. Additionally, we confirmed that redefining R-ISS at MM relapse is of high clinical value.

Analysis of Mutational Profile of Hypopharyngeal and Laryngeal Head and Neck Squamous Cell Carcinomas Identifies KMT2C as a Potential Tumor Suppressor.

Hypopharyngeal cancer is a poorly characterized type of head and neck squamous cell carcinoma (HNSCC) with bleak prognosis and only few studies focusing specifically on the genomic profile of this type of cancer. We performed molecular profiling of 48 HPV (Human Papilloma Virus)-negative tumor samples including 23 originating from the hypopharynx and 25 from the larynx using a targeted next-generation sequencing approach. Among genes previously described as significantly mutated, TP53, FAT1, NOTCH1, KMT2C, and CDKN2A were found to be most frequently mutated. We also found that more than three-quarters of our patients harbored candidate actionable or prognostic alterations in genes belonging to RTK/ERK/PI3K, cell-cycle, and DNA-damage repair pathways. Using previously published data we compared 67 hypopharyngeal cancers to 595 HNSCC from other sites and found no prominent differences in mutational frequency except for CASP8 and HRAS genes. Since we observed relatively frequent mutations of KTM2C (MLL3) in our dataset, we analyzed their role, in vitro, by generating a KMT2C-mutant hypopharyngeal cancer cell line FaDu with CRISPR-Cas9. We demonstrated that KMT2C loss-of-function mutations resulted in increased colony formation and proliferation, in concordance with previously published results. In summary, our results show that the mutational profile of hypopharyngeal cancers might be similar to the one observed for other head and neck cancers with respect to minor differences and includes multiple candidate actionable and prognostic genetic alterations. We also demonstrated, for the first time, that the KMT2C gene may play a role of tumor suppressor in HNSCC, which opens new possibilities in the search for new targeted treatment approaches.

The Clinical Tumor Lysis Syndrome in a Patient with Mixed Phenotype Acute Leukemia Undergoing Induction with Venetoclax and Azacitidine: A Case Report.

A combination of azacitidine and venetoclax (AZA-VEN) has been approved for the treatment of adult treatment-naïve acute myeloid leukemia (AML) patients, ineligible for intensive chemotherapy. The protocol may also constitute an alternative for the treatment of patients with mixed phenotype acute leukemia (MPAL), for which no established treatment guidelines exist. It may be anticipated, that alike in AML or chronic lymphocytic leukemia, the treatment of MPAL may be complicated by the tumor lysis syndrome (TLS). No case of TLS in MPAL after VEN has been however reported so far. Here, we present a case of a patient with MPAL, who received AZA-VEN. The patient had a substantial bulk of disease with generalized lymphadenopathy and increased white blood cell count. Despite preventive measures, the patient developed the clinical TLS, which was successfully treated. Based on the current case and other published cases, the incidence of TLS after AZA-VEN was established at 17%.

Epithelial Cells of Deep Infiltrating Endometriosis Harbor Mutations in Cancer Driver Genes.

Endometriosis is an inflammatory condition manifested by the presence of endometrial-like tissue outside of the uterine cavity. The most common clinical presentations of endometriosis are dysmenorrhea, infertility, and severe pelvic pain. Few hypotheses attempt to explain the pathogenesis of endometriosis; however, none of the theories have been fully confirmed or considered universal. We examined somatic mutations in eutopic endometrium samples, deep endometriotic nodules and peripheral blood from 13 women with deep endometriosis of the rectovaginal space. Somatic variants were identified in laser microdissected samples using next-generation sequencing. A custom panel of 1296 cancer-related genes was employed, and selected genes representing cancer drivers and non-drivers for endometrial and ovarian cancer were thoroughly investigated. All 59 detected somatic variants were of low mutated allele frequency (<10%). In deep ectopic lesions, detected variants were significantly more often located in cancer driver genes, whereas in eutopic endometrium, there was no such distribution. Our results converge with other reports, where cancer-related mutations were found in endometriosis without cancer, particularly recurrent KRAS mutations. Genetic alterations located in ectopic endometriotic nodules could contribute to their formation; nevertheless, to better understand the pathogenesis of this disease, more research in this area must be performed.

Co-occurrence of unclassified myeloproliferative neoplasm and giant cell arteritis in a patient treated with allogeneic hematopoietic stem cell transplantation: a case report and literature review.

Myeloproliferative neoplasms (MPNs) are a group of hematologic disorders characterized by clonal proliferation of myeloid lineage cells. The diagnostic criteria are based on morphological features of bone marrow and peripheral blood cells but also include specific genomic mutations. In some patients, co-occurrence of hematologic and rheumatic diseases could be observed. To date, most of the reported cases concerned patients with myelodysplastic syndrome (MDS) or essential thrombocythemia (ET). In this paper, we present a case of a patient with a complicated diagnostic process leading to the diagnosis of unclassified MPN and giant cell arteritis (GCA). Routine tests did not reveal any mutations typical for MPNs such as JAK-2, CALR, MPL or BCR-ABL. Targeted next-generation sequencing (NGS) helped to confirm the diagnosis by demonstrating the presence of heterozygous ASXL1, TET2, SRSF2, and CBL mutations. The second important issue was the overlapping of symptoms of MPN and seronegative rheumatic disease, which finally was diagnosed as GCA. Leukocytosis and musculoskeletal pain, which were present at the time of diagnosis, resolved after allogeneic hematopoietic stem cell transplantation but recurred after a few months along with decreasing donor cell chimerism. Differentiation of the causes of recurrence of the symptoms was an important issue. This case shows the diagnostic challenge posed by co-incidence of MPN and rheumatic disease, especially its atypical variants.

In vivo, ex vivo and in vitro dasatinib activity in chronic lymphocytic leukemia.

Dasatinib inhibits the breakpoint cluster region-Abelson murine leukemia 1 (BCR-ABL1) gene along with other kinases known to be overexpressed and abnormally active in patients with chronic lymphocytic leukemia (CLL). The current study used primary leukemic cells obtained from 53 patients with CLL that were treated with dasatinib. A 2,3-bis-(2-methoxy-4-nitro-5-sulfophenyl)-2H-tetrazolium-5-carboxanilide (XTT) assay and Annexin V staining was performed to assess the cytotoxic effects of dasatinib treatment. The XTT assay revealed that the median cytotoxicity of dasatinib was 8.30% (range, 0.00-77.89%). Due to high dispersion of dasatinib activity, patients were divided into sensitive (n=27; 50.94%; median cytotoxicity, 22.81%) and resistant groups (n=26; 49.06%; median cytotoxicity, 0.00%). A median cytotoxicity of 8.30% was selected as a cut off value. Using Annexin V staining and flow cytometry on exemplary sensitive and resistant CLL samples, it was revealed that 17.71 and 1.84% of cells were apoptotic, respectively. The current study presented a case of a patient with concomitant occurrence of CLL and chronic myeloid leukemia (CML) with a major molecular response after dasatinib treatment. A simultaneous reduction of circulating CLL cells indicated in vivo anti-CLL activity induced by dasatinib. After an in vitro culture of the patient's mononuclear cells with subsequent dasatinib treatment, a higher percentage of CLL cells undergoing apoptosis was obsevered when compared with untreated samples (38.19 vs. 21.99%, respectively). Similarly, the percentage of CLL apoptotic cells (ΔΨmlow) measured by chloromethyl-X-rosamine was higher after incubation with dasatinib (7.28%) than in the negative control (2.86%). In conclusion, dasatinib induced antileukemic effects against CML and CLL cells. The results of the current study indicated that dasatinib may induce apoptosis ex vivo, in vitro and in vivo in CLL.

Predictive significance of selected gene mutations in relapsed and refractory chronic lymphocytic leukemia patients treated with ibrutinib.

BACKGROUND: Ibrutinib, an inhibitor of the Bruton's kinase (BTK), is characterized by high efficacy in the therapy of patients with relapsed and refractory chronic lymphocytic leukemia (RR-CLL). AIMS: To analyze the potential significance of the mutational status of selected 30 genes on the disease outcome in 45 patients with RR-CLL using custom-made gene panel and sequencing on Illumina MiSeq FGx platform. RESULTS: The highest rate of mutations was observed in TP53 (n = 18; 40.0%), NOTCH1 (n = 13; 28.8%), SF3B1 (n = 11; 24.4%), ATM (n = 7; 15.6%), MED12 (n = 6, 13.3%), CHD2 (n = 5; 11.1%), XPO1 (n = 5; 11.1%), NFKBIE (n = 5; 11.1%), BIRC3 (n = 4; 8.9%), SPEN (n = 4; 8.9%), POT1 (n = 4; 8.9%), EGR2 (n = 3; 6.7%), and RPS15 (n = 3; 6.7%). With a median observation time of 45.9 months, the median progression-free survival (PFS) and overall survival (OS) were not reached. The 36-month estimated rate of PFS and OS were 64% and 68.2%, respectively. The overall response rate was noted in 23 patients (51.1%), while twenty (44.4%) patients achieved stability. Progression was noted in 2 (4.5%) cases. Analyzed molecular factors had no impact on PFS and OS. CONCLUSION: Despite accumulation of several poor prognostic factors in our real-life cohort of heavily pretreated patients with CLL, ibrutinib treatment showed long-term clinical benefit.

Whole-exome sequencing in patients with protein aggregate myopathies reveals causative mutations associated with novel atypical phenotypes.

BACKGROUND: Myofibrillar myopathies (MFM) are a subgroup of protein aggregate myopathies (PAM) characterized by a common histological picture of myofibrillar dissolution, Z-disk disintegration, and accumulation of degradation products into inclusions. Mutations in genes encoding components of the Z-disk or Z-disk-associated proteins occur in some patients whereas in most of the cases, the causative gene defect is still unknown. We aimed to search for pathogenic mutations in genes not previously associated with MFM phenotype. METHODS: We performed whole-exome sequencing in four patients from three unrelated families who were diagnosed with PAM without aberrations in causative genes for MFM. RESULTS: In the first patient and her affected daughter, we identified a heterozygous p.(Arg89Cys) missense mutation in LMNA gene which has not been linked with PAM pathology before. In the second patient, a heterozygous p.(Asn4807Phe) mutation in RYR1 not previously described in PAM represents a novel, candidate gene with a possible causative role in the disease. Finally, in the third patient and his symptomatic daughter, we found a previously reported heterozygous p.(Cys30071Arg) mutation in TTN gene that was clinically associated with cardiac involvement. CONCLUSIONS: Our study identifies a new genetic background in PAM pathology and expands the clinical phenotype of known pathogenic mutations.

Differential Regulation of Telomeric Complex by BCR-ABL1 Kinase in Human Cellular Models of Chronic Myeloid Leukemia-From Single Cell Analysis to Next-Generation Sequencing.

Telomeres are specialized nucleoprotein complexes, localized at the physical ends of chromosomes, that contribute to the maintenance of genome stability. One of the features of chronic myeloid leukemia (CML) cells is a reduction in telomere length which may result in increased genomic instability and progression of the disease. Aberrant telomere maintenance in CML is not fully understood and other mechanisms such as the alternative lengthening of telomeres (ALT) are involved. In this work, we employed five BCR-ABL1-positive cell lines, namely K562, KU-812, LAMA-84, MEG-A2, and MOLM-1, commonly used in the laboratories to study the link between mutation, copy number, and expression of telomere maintenance genes with the expression, copy number, and activity of BCR-ABL1. Our results demonstrated that the copy number and expression of BCR-ABL1 are crucial for telomere lengthening. We observed a correlation between BCR-ABL1 expression and telomere length as well as shelterins upregulation. Next-generation sequencing revealed pathogenic variants and copy number alterations in major tumor suppressors, such as TP53 and CDKN2A, but not in telomere-associated genes. Taken together, we showed that BCR-ABL1 kinase expression and activity play a crucial role in the maintenance of telomeres in CML cell lines. Our results may help to validate and properly interpret results obtained by many laboratories employing these in vitro models of CML.

Germline missense NF1 mutation in an elderly patient with a blastic plasmacytoid dendritic cell neoplasm.

Neurofibromatosis type 1 is an autosomal dominantly inherited tumor predisposition syndrome, in which inactivating mutations in the neurofibromatosis type 1 gene (NF1) lead to a prolonged activation of the signaling via the RAS/RAF/MAPK pathway leading to loss of growth control and increased cellular proliferation. We report a case of a 78-year-old man, a carrier of the germline NF1 Ala1224Gly/c.3671 C>G mutation, with ASXL1, ZRSR2 and TET2 mutation-positive blastic plasmacytoid dendritic cell neoplasm (BPDCN). Consistent with previously reported data on the role of the NF1 mutations in the pathogenesis of dendritic cell neoplasms, we suggest that the NF1 germline mutation may also increase the risk of BPDCN.

Tyrosine kinase inhibitor-induced defects in DNA repair sensitize FLT3(ITD)-positive leukemia cells to PARP1 inhibitors.

Mutations in FMS-like tyrosine kinase 3 (FLT3), such as internal tandem duplications (ITDs), can be found in up to 23% of patients with acute myeloid leukemia (AML) and confer a poor prognosis. Current treatment options for FLT3(ITD)-positive AMLs include genotoxic therapy and FLT3 inhibitors (FLT3i's), which are rarely curative. PARP1 inhibitors (PARP1i's) have been successfully applied to induce synthetic lethality in tumors harboring BRCA1/2 mutations and displaying homologous recombination (HR) deficiency. We show here that inhibition of FLT3(ITD) activity by the FLT3i AC220 caused downregulation of DNA repair proteins BRCA1, BRCA2, PALB2, RAD51, and LIG4, resulting in inhibition of 2 major DNA double-strand break (DSB) repair pathways, HR, and nonhomologous end-joining. PARP1i, olaparib, and BMN673 caused accumulation of lethal DSBs and cell death in AC220-treated FLT3(ITD)-positive leukemia cells, thus mimicking synthetic lethality. Moreover, the combination of FLT3i and PARP1i eliminated FLT3(ITD)-positive quiescent and proliferating leukemia stem cells, as well as leukemic progenitors, from human and mouse leukemia samples. Notably, the combination of AC220 and BMN673 significantly delayed disease onset and effectively reduced leukemia-initiating cells in an FLT3(ITD)-positive primary AML xenograft mouse model. In conclusion, we postulate that FLT3i-induced deficiencies in DSB repair pathways sensitize FLT3(ITD)-positive AML cells to synthetic lethality triggered by PARP1i's. Therefore, FLT3(ITD) could be used as a precision medicine marker for identifying AML patients that may benefit from a therapeutic regimen combining FLT3 and PARP1i's.