Binding Factor Acute Myeloid Leukemia Research Articles

Hypomethylating agent monotherapy in core binding factor acute myeloid leukemia: a French multicentric retrospective study

Very few data are available about hypomethylating agent (HMA) efficiency in core binding factor acute myeloid leukemias (CBF-AML). Our main objective was to evaluate the efficacy and safety of HMA in the specific subset of CBF-AML. Here, we report the results of a multicenter retrospective French study about efficacy of HMA monotherapy, used frontline or for R/R CBF-AML. Forty-nine patients were included, and received a median of 5 courses of azacitidine (n = 46) or decitabine (n = 3). ORR was 49% for the whole cohort with a median time to response of 112 days. After a median follow-up of 72.3 months, median OS for the total cohort was 10.6 months. In multivariate analysis, hematological relapse of CBF-AML at HMA initiation was significantly associated with a poorer OS (HR: 2.13; 95%CI: 1.04–4.36; p = 0.038). Responders had a significantly improved OS (1-year OS: 75%) compared to non-responders (1-year OS: 15.3%; p < 0.0001). Hematological improvement occurred for respectively 28%, 33% and 48% for patients who were red blood cell or platelet transfusion-dependent, or who experienced grade 3/4 neutropenia at HMA initiation. Adverse events were consistent with the known safety profile of HMA. Our study highlights that HMA is a well-tolerated therapeutic option with moderate clinical activity for R/R CBF-AML and for patients who cannot handle intensive chemotherapy.

Prevalence and Prognosis of Secondary Genetic Aberrations Among Patients With Core Binding Factor Acute Myeloid Leukemia: A Mitelman Database Analysis.

Core binding factor acute myeloid leukemia (CBF-AML) comprises t(8;21) and inv(16) and usually has a favorable prognosis. However, a wide spectrum of secondary genetic aberrations has been shown to be associated with worse outcomes with respect to overall survival (OS) and relapse. We aimed to identify secondary molecular and chromosomal aberrations within each group of CBF-AML, i.e., t(8;21) and inv(16), and to evaluate their prognosis with OS. Using the Mitelman Database of Chromosome Aberrations and Gene Fusions in Cancer, we analyzed 193 cases of CBF-AML reported between 2011 and 2021. We conducted a survival analysis to determine the 5-year OS, and we conducted univariate and multivariate Cox regression to identify independent genetic factors related to OS. Among the 193 cases with CBF-AML, structural and numerical chromosome rearrangements were 25.9% and 40.9%, respectively, and secondary genetic mutations were 54.9%. The 5-year OS for the presence of del(7) and trisomy 22 was significantly worse. NRAS mutations had a worse 5-year OS in the t(8;21) group in the univariate analysis but showed no significant difference in the multivariate analysis. CBF-AML has heterogeneous cytogenetic characteristics but no difference in the 5-year OS between the inv(16) and t(8;21) groups. Finally, the presence of del(7), trisomy 22 and NRAS mutations showed a potential prognostic impact in CBF-AML patients. Secondary genetic findings may need to be identified to determine its association to a worse prognosis, and in the future develop better targeted therapies in patients with CBF-AML.

Clinical characteristics and prognostic factors analysis of core binding factor acute myeloid leukemia in real world.

Chromosomal translocations involving core binding factor (CBF) genes account for 15% of adult acute myeloid leukemia (AML) cases in China. Despite being classified as favorable-risk by European Leukemia Net (ELN), CBF-AML patients have a 40% relapse rate. This study aims to analyze clinical characteristics and prognosis of CBF-AML, compare its subtypes (inv(16) and t(8;21)), and validate prognostic factors. Retrospective analysis of 149 AML patients (75 CBF-AML, 74 non-CBF) at Peking University First Hospital (March 2012-March 2022). CBF-AML patients have significantly lower disease-free survival (DFS) (p = 0.005) and higher non-relapse mortality (NRM) (p = 0.028) compared to non-CBF AML. inv (16) and t(8;21) show distinct co-occurring gene mutation patterns, with inv(16) being prone to central nervous system (CNS) leukemia. Multivariate analysis identifies age as a risk factor for overall survival (OS) and disease free survival (DFS), kinase mutation as a risk factor for DFS and Recurrence, while WT1 mutation as a risk factor for OS and non relapse mortality (NRM) risk in t(8;21) AML. Allogeneic hematopoietic stem cell transplantation (allo-HSCT) improves prognosis in low-risk t(8;21). Prognosis of CBF-AML is poorer than ELN guidelines suggest. inv(16) and (8;21) are separate entities with relatively poor prognoses, requiring rational risk stratification strategies. Allo-HSCT may benefit low-risk t(8;21), but further research is needed for conclusive evidence.

Residual Mast Cells Can Explain Persistent Molecular Positivity in Difference from Normal Flow Cytometric-Defined MRD Negative Core Binding Factor AML

Introduction: Core binding factor acute myeloid leukemia (CBF-AML) accounts for 30% of pediatric and 15% adult AMLs and is defined by fusions involving RUNX1 or CBFB. RT-PCR is commonly used to monitor measurable residual disease (MRD) in patients with CBF-AML. However, it has been reported that these fusions can be detected in patients during complete remission (CR) or after hematopoietic cell transplant (HCT). This raises the question of if these patients should be considered MRD positive, given they appear otherwise disease free. We utilized flow cytometric cell sorting and fluorescent in situ hybridization (FISH) to determine the source of persistent CBF fusions. Methods: Flow cytometry was used to isolate mast cells (CD117 bright/CD34 negative) from 13 patients with CBF-AML fusions (8 RUNX1:: RUNX1T1 and 5 CBFB:: MYH11) alongside progenitor cells (CD34+/CD117 heterogeneous, 12 patients) and T cells (CD3+, 11 patients) as available for FISH analysis. These patients were fusion positive by RT-PCR but had no evidence of MRD by difference from normal multidimensional flow cytometry (ΔN), the gold standard for determination of residual disease in Children's Oncology Group-sponsored clinical trials for AML. Cells were sorted from 6 additional patients with a history of RUNX1:: RUNX1T1 CBF-AML who were MRD negative by ΔN but without RT-PCR results available. Results: In 11/13 patients, the mast cell fraction was positive for the CBF fusion but all other sorted cell fractions tested were negative. In the remaining two specimens, all cell fractions were negative, likely due to FISH sensitivity compared to RT-PCR. Both CBF fusions exhibited the same pattern, with fusions detected only in the mast cell fractions (7 RUNX1:: RUNX1T1 and 4 CBFB:: MYH11). The additional 6 patients who were MRD negative by ΔN but without RT-PCR data followed the same pattern, with RUNX1:: RUNX1T1 detected by FISH in the mast cells (6/6 patients) and not in other sorted populations (5/6 patients sorted for progenitor and T cells). Two patients had a clinical history of CBF-AML and systemic mastocytosis (SM). ΔN revealed no evidence of residual AML but showed abnormal mast cells with expression of CD2 and CD25, consistent with abnormalities associated with SM. FISH analysis of sorted mast cells revealed the presence of the RUNX1:: RUNX1T1 fusion, while progenitor and T cells were both negative. In all other patients the mast cells showed no phenotypic abnormalities, demonstrating that CBF fusions can be detected in both phenotypically normal and abnormal mast cells in patients who are free of residual AML. Two patients with CBFB:: MYH11 fusions had specimens evaluated by FISH on sorted cells over a month apart where the fusion persisted only in the mast cells. Two patients with RUNX1:: RUNX1T1 fusions had serial specimens analyzed at 4 different timepoints. One patient had fusion positive mast cells for over 8 months after residual disease was last detected by ΔN. The other patient, who had previously undergone HCT, harbored fusion positive mast cells for 13 months. Both patients remained MRD negative by ΔN over the course of testing. Discussion: These data demonstrate that in CBF-AML, fusions can be detected exclusively in the mast cells of otherwise leukemia-free patients, resulting in positive RT-PCR results in the absence of any other disease pathology. These mast cells can be normal or abnormal and can persist after successful HCT. Given that these patients are free of disease by other measures, these fusion positive mast cells do not appear to contribute to AML pathogenesis. Additionally, this post-HCT fusion positive persistence demonstrates a potential clinical implication: if patients such as reported here are assessed pre-transplant using RT-PCR on unsorted specimens alone, they may not be considered candidates for HCT even though the fusion is confined to terminally differentiated cells and successful transplant can be achieved. For these reasons, while RT-PCR is a specific and accurate assay, caution is required for CBF-AML patients. Flow cytometry and cell sorting in combination with genetic testing, in this case FISH, protect against these mast cell driven positive results and provide an accurate assessment of disease status. These data highlight the importance of considering AML biology and combining multiple testing methods to monitor AML patients comprehensively and accurately.

KIT exon 17 mutations are predictive of inferior outcome in pediatric acute myeloid leukemia with RUNX1::RUNX1T1.

Pediatric core binding factor acute myeloid leukemia (CBF-AML), although considered a favorable risk subtype, exhibits variable outcomes primarily driven by additional genetic abnormalities, such as KIT mutations. In this study, we examined the prognostic impact of KIT mutations in 130 pediatric patients with CBF-AML, treated uniformly at a single center over 4years (2017-2021). KIT mutations were detected via next-generation sequencing using a myeloid panel comprising 52 genes for most patients. Our findings revealed that KIT mutations were present in 31% of CBF-AML cases. Exon 17 KIT mutation was most commonly (72%) seen with notable occurrences at the D816 and N822 residue in 48% and 39% of cases, respectively. The 3-year cumulative incidence of relapse (CIR) and overall survival (OS) for patients with exon 17 KIT mutation were 36% and 40%, respectively, and was significantly worse in comparison to other site KIT mutations (3-year CIR: 11%; OS: 64%) and without KIT mutation (3-year CIR: 13%; OS:71%). Notably, the prognostic impact of KIT mutations was prominent in patients with RUNX1::RUNX1T1, but not in those with CBFB::MYH11 fusion. Additionally, a high KIT variant-allele frequency (VAF) (>33%) predicted for a higher disease relapse; 3-year CIR of 40% for VAF greater than 33% versus 7% for VAF less than 33%. When adjusted for site of KIT mutation and end-of-induction measurable residual disease, VAF greater than 33% correlated with poor OS (hazard ratio [HR]: 4.4 [95% CI: 1.2-17.2], p=.034). Exon 17 KIT mutations serve as an important predictor of relapse in RUNX1::RUNX1T1 pediatric AML. In addition, a high KIT VAF may predict poor outcomes in these patients. These results emphasize the need to incorporate KIT mutational analysis into risk stratification for pediatric CBF-AML.

[Clinical features and prognosis of core binding factor acute myeloid leukemia children in South China: a multicenter study].

Objective: To analyze the clinical features, efficacy and prognosis factors of core binding factor (CBF) acute myeloid leukemia (AML) children in South China. Methods: This was a retrospective cohort study. Clinical data of 584 AML patients from 9 hospitals between January 2015 to December 2020 was collected. According to fusion gene results, all patients were divided into two groups: CBF-AML group (189 cases) and non-CBF-AML group (395 cases). CBF-AML group were divided into AML1-ETO subgroup (154 cases) and CBFβ-MYH11 subgroup (35 cases). Patients in CBF-AML group chosen different induction scheme were divided into group A (fludarabine, cytarabine, granulocyte colony stimulating factor and idarubicin (FLAG-IDA) scheme, 134 cases) and group B (daunorubicin, cytarabine and etoposide (DAE) scheme, 55 cases). Age, gender, response rate, recurrence rate, mortality, molecular genetic characteristics and other clinical data were compared between groups. Kaplan-Meier method was used for survival analysis and survival curve was drawn. Cox regression model was used to analyze prognostic factors. Results: A total of 584 AML children were diagnosed, including 346 males and 238 females. And a total of 189 children with CBF-AML were included, including 117 males and 72 females. The age of diagnosis was 7.3 (4.5,10.0)years, and the white blood cell count at initial diagnosis was 21.4 (9.7, 47.7)×109/L.The complete remission rate of the first course (CR1) of induction therapy, relapse rate, and mortality of children with CBF-AML were significantly different from those in the non-CBF-AML group (91.0% (172/189) vs. 78.0% (308/395); 10.1% (19/189) vs. 18.7% (74/395); 13.2% (25/189) vs. 25.6% (101/395), all P<0.05). In children with CBF-AML, the CBFβ-MYH11 subgroup had higher initial white blood cells and lower proportion of extramedullary invasion than the AML1-ETO subgroup, with statistical significance (65.7% (23/35) vs. 14.9% (23/154), 2.9% (1/35) vs. 16.9% (26/154), both P<0.05). AML1-ETO subgroup had more additional chromosome abnormalities (75/154), especially sex chromosome loss (53/154). Compared with group B, group A had more additional chromosome abnormalities and a higher proportion of tumor reduction regimen, with statistical significance (50.0% (67/134) vs. 29.1% (16/55), 34.3% (46/134) vs. 18.2% (10/55), both P<0.05). Significant differences were found in 5-years event free survival (EFS) rate and 5-year overall survival (OS) rate between CBF-AML group and non-CBF-AML group ((77.0±6.4)%vs. (61.9±6.7)%,(83.7±9.0)%vs. (67.3±7.2)%, both P<0.05).EFS and OS rates of AML1-ETO subgroup and CBFβ-MYH11 subgroup in children with CBF-AML were not significantly different (both P>0.05). Multivariate analysis showed in the AML1-ETO subgroup, CR1 rate and high white blood cell count (≥50×109/L) were independent risk factors for EFS (HR=0.24, 95%CI 0.07-0.85,HR=1.01, 95%CI 1.00-1.02, both P<0.05) and OS (HR=0.24, 95%CI 0.06-0.87; HR=1.01, 95%CI 1.00-1.02; both P<0.05). Conclusions: In CBF-AML, AML1-ETO is more common which has a higher extramedullary involvement and additional chromosome abnormalities, especially sex chromosome loss. The prognosis of AML1-ETO was similar to that of CBFβ-MYH11. The selection of induction regimen group FLAG-IDA for high white blood cell count and additional chromosome abnormality can improve the prognosis.

POSTER: AML-316 Clinical Outcomes of Adults With Core Binding Factor Acute Myeloid Leukemia (CBF-AML): A Single Center Experience

POSTER: AML-316 Clinical Outcomes of Adults With Core Binding Factor Acute Myeloid Leukemia (CBF-AML): A Single Center Experience

AML-316 Clinical Outcomes of Adults With Core Binding Factor Acute Myeloid Leukemia (CBF-AML): A Single Center Experience

AML-316 Clinical Outcomes of Adults With Core Binding Factor Acute Myeloid Leukemia (CBF-AML): A Single Center Experience

Comparison of efficacy between homoharringtonine, aclarubicin, cytarabine (HAA) and idarubicin, cytarabine (IA) regimens as induction therapy in patients with de novo core binding factor acute myeloid leukemia.

To compare efficacy between homoharringtonine combined with cytarabine and aclarubicin (HAA) and idarubicin and cytarabine (IA) regimens as first induction chemotherapy in patients with core binding factor acute myeloid leukemia (CBF-AML). Cox regression model and propensity score matching (PSM) were used to identify the regimen associated with a better remission rate and outcomes. In total, 374 patients with CBF-AML (243 with RUNX1::RUXN1T1 and 131 with CBFB::MYH11) were included in this study. The patients received the HAA or IA regimen (187 each) as the first induction therapy. For patients with RUNX1::RUXN1T1, multivariate analyses showed that the HAA regimen was significantly associated with a higher CR/CRi rate after the first induction (hazard ratio [HR] = 5.3 [95% CI 2.3, 12.2]; p < 0.001) and more favorable relapse-free survival (RFS) (HR = 0.5 [0.3, 0.8], p = 0.01). In PSM analysis, the HAA regimen also had a higher CR/CRi rate (96% vs. 77%, p < 0.001), especially for those harboring wild-type KIT (KITWT) (96% vs. 83%, p = 0.02) or non-D816 KIT mutation (100% vs. 63%, p = 0.002), as well as more favorable RFS (p = 0.01), compared with the IA regimen. However, there was no difference in the remission rate or outcomes between the two regimens for patients with CBFB::MYH11. The HAA regimen as first induction chemotherapy resulted in a higher CR/CRi rate in AML patients with RUNX1::RUNX1T1, especially those harboring KITWT and non-D816 KIT mutation, and a more favorable RFS compared with the IA regimen. The efficacy between the two regimens did not differ in those with CBFB::MYH11.

Treatment phase stratified outcomes of core binding factor acute myeloid leukemia.

e19055 Background: Mutations in core binding factor (CBF) are associated with a favorable prognosis in acute myeloid leukemia (AML). However, between 30-40% of patients with CBF-AML relapse, and relative outcomes with each subsequent line of therapy remain unclear. Additionally, the overall survival of CBF-AML compared to other favorable risk molecular aberrations — such as NPM1mut and CEBPA — is unknown in light of the addition of monoallelic CEBPA in ELN 2022. Therefore, the purpose of this study was to clarify the outcomes of CBF-AML relative to other favorable risk aberrations and to determine the relative overall survival associated with each subsequent relapse. Methods: We retrospectively analyzed 46 consecutive patients with CBF-AML treated from January 2013 to January 2022 at VCU Massey Cancer Center that underwent intensive chemotherapy (IC) with or without gemtuzumab ozogamicin. During the same study period, we analyzed a comparison cohort of 272 consecutive patients: 103 ELN 2017 intermediate-risk patients, 111 adverse-risk patients, eight patients with mono- or biallelic mutations in CEBPA, and 50 with ELN 2017 favorable-risk NPM1mut. All patients were treated with front-line IC. We analyzed survival by the Kaplan-Meier method and compared groups with the log-rank test. Results: We analyzed 46 patients with CBF-AML across 136 treatment phases. Patients with CBF-AML had superior overall survival compared to patients with NPM1mut (median overall survival not reached at a median follow-up time of 5.0 years versus 21.0 m., p = 0.028). There were no differences in survival between CBF-AML and AML with monoallelic or biallelic mutations in CEBPA at a median follow-up time of 3.7 years (not reached, p = 0.976). Expectedly, the overall survival for CBF-AML was superior to ELN 2017 intermediate (30.1 m., p = 0.011) and adverse (10.9 m., p &lt; 0.0001) risk disease. Next, we analyzed survival trends in the relapsed or refractory setting for CBF-AML by lines of therapy, using ELN 2017 intermediate and adverse risk cohorts as a comparison. During the first relapse, CBF-AML was associated with a significantly superior overall survival compared to the adverse cohort (19.1 m. versus 10.0 m., p = 0.024) but not the intermediate cohort (14.5 m., p = 0.734). The absence of KITmut was not associated with improved survival compared to the ELN 2017 intermediate category at the first relapse ( p = 0.610). At the second relapse, the survival disparity disappeared between the CBF-AML and adverse risk groups (7.7 m. vs 4.0 m., p = 0.964). Conclusions: CBF-AML was associated with similar survival to mono- or biallelic mutations in CEBPA, and significantly prolonged overall survival compared to NPM1mut. Relative to a matched cohort of adverse-risk AML at the time of the first relapse, outcomes of relapsed CBF-AML remain favorable. The relative overall survival benefit of CBF-AML disappeared at the time of the second relapse.

Clinical outcomes of core binding factor acute myeloid leukemia in the modern era.

e19054 Background: Acute myeloid leukemia (AML) with alterations in core binding factor (CBF) has a favorable prognosis. The impact of complex cytogenetics or ELN 2022 adverse genetic risk markers — such as ASXL1, RUNX1, EZH2, SRSF2, (and the rest of the secondary-type mutations [STMs]) and TP53 — in CBF-AML is unclear. Additionally, treatment outcomes in CBF-AML using front-line novel approaches, such as a hypomethylating agent (HMA; decitabine or azacitidine) with venetoclax, are unknown. This study analyzed outcomes of CBF-AML with respect to higher-risk molecular and cytogenetic cohorts and treatment approaches. Methods: We identified 58 consecutive patients with CBF-AML treated at VCU Massey Cancer Center from January 1, 2013 to January 1, 2022. We used Fisher’s exact test for between-group comparisons. We analyzed survival by the Kaplan-Meier method and compared groups with the log-rank test. The date of death was used to calculate overall survival; patients were censored at the date of the last contact. Measurable residual disease (MRD) was assessed using PCR-based methods or multiparameter flow cytometry with a minimum sensitivity of 10-3. Results: We analyzed 58 patients with inv(16) or t(8;21) AML treated in the front-line setting. Seven of these patients had concomitant genetic or molecular abnormalities typically considered high risk, including complex cytogenetics or TP53mut. Forty-nine (84.5%) patients received intensive chemotherapy (IC) with FLAG, CPX-351, or conventional 7+3 with or without gemtuzumab ozogamicin; nine patients (15.5%) received lower-intensity therapies with HMAs with or without venetoclax. No differences in overall survival were seen between the patients with CBF-AML with or without complex cytogenetics or TP53mut (not reached for either cohort, median follow-up time of 6.1 y. and 5.0 y., respectively, p = 0.969). There was no difference in the rates of MRD negativity in CBF-AML with or without complex cytogenetics or TP53mut ( p = 0.544). The presence of secondary-type mutations also did not appear to significantly impact survival in CBF-AML ( p = 0.654). There was no difference in the rates of MRD negativity in CBF-AML with STMs and those without STMs ( p = 0.500). Patients that were ineligible for IC and were treated with venetoclax + HMA or HMA monotherapy had significantly reduced composite complete remission rates (CRR; CR + CRi; 25% vs 91.3%, p = 0.007) and median overall survival (3.7 m. versus not reached, p = 0.038). Conclusions: Our data confirm the superior outcomes in induction candidates of CBF-AML treated with IC. The presence of complex cytogenetics, TP53mut, or secondary-type mutations did not appear to influence the rates of MRD negativity or overall survival in CBF-AML.

CAG (cytarabine, aclarubicin and granulocyte colony-stimulating factor) regimen for core binding factor acute myeloid leukaemia with measurable residual disease.

Acute myeloid leukaemia (AML) with t (8;21) or inv (16), called core binding factor (CBF) AML, has a favourable prognosis. However, some CBF-AML patients have persistent measurable residual disease (MRD) and are more likely to relapse after standard chemotherapy treatment. The CAG regimen, composed of cytarabine, aclarubicin and granulocyte colony-stimulating factor, has been proven to be effective and safe in treating refractory AML patients. We performed a retrospective study to evaluate the efficacy of the CAG regimen to eliminate MRD detected by RUNX1::RUNX1T1 and CBFβ::MYH11 transcript levels by quantitative polymerase chain reaction (Q-PCR) among 23 patients. Molecular response was defined as the ratio of fusion transcript after treatment to that before treatment less than or equal to 0.5. The molecular response rate and median decrease ratio of fusion transcripts at the molecular level of the CAG regimen were 52% and 0.53, respectively. The median fusion transcripts before CAG treatment was 0.25% whereas after CAG was 0.11%. Among the 15 patients who had a poor molecular response to the high/intermediate-dose cytarabine regimen, the median decrease ratios of transcripts at the molecular level of high/intermediate-dose cytarabine and CAG were 1.55 and 0.53 (P = 0.028), respectively, and 6 of 15 patients achieved a molecular response to CAG (40%). The median disease-free survival was 18months, and the overall survival rate at 3years among all patients was 72.7% ± 10.7%. The common grades 3-4 adverse events were nausea (100%), thrombocytopenia (39%) and neutropenia (37.5%). The CAG regimen may have activity in CBF-AML patients and could provide a new option for patients who have a poor molecular response to high/intermediate-dose cytarabine.

Therapy-related core binding factor acute myeloid leukemia.

Therapy-related acute myeloid leukemia (t-AML) usually stems from exposure of the bone marrow to cytotoxic chemotherapy and/or radiation therapy. t-AML is usually associated with poor overall survival, but occasionally t-AML can involve favorable-risk cytogenetics, including core binding factor AML (CBF-AML), which shows a recurrent chromosomal rearrangement with t(8;21) (q22;22) and 'inv(16) (p13.1;q22)/t(16;16)(p13.1;q22)', leading to 'RUNX1::RUNX1T1 and CBFB::MYH11' fusion genes, respectively. Therapy-related CBF-AML (t-CBF-AML) accounts for 5-15% of CBF-AML cases and tends to have better outcomes than t-AML with unfavorable cytogenetics. Although CBF-AML is sensitive to high-dose cytarabine, t-CBF-AML has worse overall survival than de novo CBF- AML. The objective of this review is to discuss the available data on the pathogenesis, mutations, and therapeutic options in patients with t-CBF-AML.

Drivers of Deep Molecular Response and Outcomes in Patients with Core Binding Factor Acute Myeloid Leukemia

Introduction: Core-binding factor acute myeloid leukemia (CBF-AML), including t (8;21) and Inv (16), constitutes 15% of all AML cases and generally carries a favorable prognosis. However, relapse rate is ≈ 30% and predictors are not well understood. Although CBF-AML responds to induction chemotherapy, post-remission treatment can be further optimized, particularly with current next generation sequencing (NGS) and measurable residual disease (MRD) detection techniques. Impact of baseline somatic mutations on outcomes remains unclear, as does role of allogeneic stem cell transplant (allo-SCT). In this study, we investigated the potential drivers of treatment response and overall outcomes in CBF-AML. Methods: In this single center retrospective study, clinical, demographic, and molecular data were collected from adult pts with CBF-AML who were treated at Moffitt Cancer Center. We included pts with MRD by polymerase chain reaction (PCR) for CBF abnormality (CBF-MRD) results available from time of induction and consolidation. All statistical analyses were performed in SPSS. Results: Our study included 68 patients (pts), including 26 (38%) t (8;21) AML. The median age at diagnosis was 48 years, and 54% pts were male. Pts with inv (16) AML had significantly more leukocytosis than t (8;21) (10x109/L vs. 23x109/L; p=0.001). Only 5% of pts (n=3) in our cohort had extramedullary disease on presentation. Common mutations identified on baseline NGS (n=60) were KIT (35%), NRAS (27%), KRAS (15%), FLT3-ITD and FLT3-TKD (12% each; 2 pts had both types). Mutation in KIT was more common in t (8;21) AML (50% vs. 25%; p=0.04), whereas inv (16) cases were enriched in NRAS mutations (36% vs. 13%; p=0.04). Overall, 80% of CBF-AML pts had at least one kinase mutation (KIT/RAS/FLT3). Majority of pts were treated with "7+3" (44%) and "7+3+ gemtuzumab ozagamicin (GO)" (40%) as induction regimens (Table 1). Daunorubicin was the predominant anthracycline, used in 80% of pts treated with "7+3" and 48% received dose of 90 mg/m2. Overall, 31 (46%) pts received GO as part of induction treatment, with equal distribution of "day 1 only" and "day 1,4,7" schedules at 3mg/m2. Median number of consolidation cycles was 3, and GO was incorporated in consolidation (commonly with high dose cytarabine) for 29 (43%) pts. After induction, 16% pts experienced CBF-MRD negativity which increased to 73% following consolidation, with no significant difference between t (8;21) and inv (16) AML. Use of GO during induction or consolidation was associated with significantly higher CBF-MRD negativity rate at completion of induction and consolidation (83% vs. 50%; p= 0.021). However, we did not find any significant correlation between groups based on presence of baseline kinase mutation/s and CBF-MRD negativity at end of induction or consolidation. In FLT3-positive cases, 100% of pts (5/5 evaluated;4 ITD and 1 TKD) achieved FLT3-MRD negativity by PCR (sensitivity of 5X10-5) following consolidation. Overall, 35% of pts (n=24) underwent allo-SCT in our cohort, including 15 in first remission (CR1). Kinase mutations were present at baseline in majority of these pts (75%; 87% in CR1 group). Notably, 9 pts (7 in CR1 group) in the allo-SCT cohort had positive CBF-MRD at the end of consolidation. Seven pre-transplant CBF-MRD positive cases turned MRD negative following allo-SCT. Relapse rate was low (n=10; 15%) in our CBF-AML pt population. Among pts with relapse, 6 were CBF-MRD positive post-induction and 3 had MRD even after consolidation. Use of GO in induction was associated with significantly lower relapse rate (0% vs. 28%; p= 0.001). Presence of kinase (KIT/RAS/FLT3) mutation at diagnosis was associated with shorter relapse free survival (RFS) in these pts (median RFS- 7.7 vs. 12.9 months (mo); p= 0.014; Figure 1). After a median follow up of 33.4 mo, median OS was 94.1 mo in our pt cohort. There was no significant OS difference between subgroups based on CBF-AML subtype, baseline mutations, or receipt of GO during treatment. Conclusions: CBF-AML continues to be a favorable risk disease, with a median OS >7 years in our study population. Post-treatment CBF-MRD negativity rate was 73% and was predicted by the incorporation of GO in induction or consolidation. Rate of relapse rate was low at 15%, and all occurred in pts who did not receive GO during induction or consolidation. Baseline kinase mutations (KIT/RAS/FLT3) on NGS was associated with a shorter RFS in our cohort. Figure 1View largeDownload PPTFigure 1View largeDownload PPT Close modal

Identification and in silico analysis of noval alteration Arg420Gly in KIT proto oncogene among acute myeloid leukemia patients

A number of studies have reported frequent incidence of c-kit gene mutations in association with core binding factor acute myeloid leukemia (CBF-AML). These genetic changes have become important prognostic predictors in patients with abnormal karyotype. Aim of this study was the detection of nucleotide alterations in newly diagnosed acute myeloid leukemia patients for three exons of c-kit gene, including cytogenetically normal patients. Thirty-one de novo AML patients were screened for any possible variations in exon 8, 11 and 17 sequences of c-kit proto-oncogene leading to amino acid substitutions or frame shift. Sanger sequencing method was employed followed by sequence analysis. Mutation data was then correlated with clinical and hematological parameters of patients and prognostic significance of genetic changes was assessed as well. The computational tools were then used to further understand the extent of damage caused by these mutations to c-kit protein. Fifteen (48.4%) mutant patients were observed with single, double or multiple mutations in one, two or all three exons studied. The analysis revealed eight new alterations which were not reported previously. Significant variation among mutant and non-mutant group of patients was observed with respect to FAB subtypes (x2 = 12.524, p = 0.029), Spleen size (x2 = 4.288, p = 0.038) and Red blood cell count (x2 = 8.447, p = 0.007). The survival analysis indicates poor overall and event free survival outcomes in mutant individuals. Furthermore, the in silico analysis suggests that changes in nucleotide sequences can possibly damage the protein structure and effect it’s function. This study emphasizes the need to consider screening of c-kit gene alterations not only in CBF-AML but in cytogenetically normal AML patients as well. In current investigation the effect of mutation Arg420Gly on structure and function of c-kit protein was investigated, as this was the most observed substitution in present cohort. Various bioinformatics tools and techniques were employed, which determined that Arg420Gly is possibly non-pathogenic mutation.

AML-488 Impact of Somatic Mutations on Treatment Response and Outcomes in Patients With Core Binding Factor Acute Myeloid Leukemia

Prognostic significance of somatic mutations remains unclear in patients with core binding factor acute myeloid leukemia (CBF-AML), especially with advanced next generation sequencing (NGS) and measurable residual disease (MRD) detection techniques. To estimate the distribution of mutations and to assess their impact on outcomes in CBF-AML. Single-center retrospective study Patients: Adults with newly diagnosed CBF-AML Main Outcome Measures: MRD negativity, relapse free survival, overall survival Results: Our study includes 59 patients (mean age- 48 years) with CBF-AML [t(8;21), n=21 and Inv(16), n=38], with available NGS and CBF-MRD results during primary treatment. Most common mutations at diagnosis included KIT (31%), NRAS (26%), KRAS (15%), FLT3-TKD (11%), and FLT3-ITD (9%). Mutations in NRAS were enriched (32%) in Inv(16) AML, whereas KIT mutations were common (45%) in association with t(8;21). No pathogenic mutation was noted in 17% of patients. Most common induction regimen was "7+3" (48%), followed by "7+3+GO" (37%), with 36% receiving gemtuzumab ozogamicin (GO) in consolidation (median- 3 cycles). CBF-MRD negativity was 15% at the end of induction, which increased to 70% after consolidation, with no significant difference between patients with or without common kinase mutations (KIT, RAS, or FLT3). In the t(8;21) AML, CBF-MRD negativity rate was lower in KIT-mutant vs. wild type (38% vs. 75%) patients, although it was not statistically significant (p = 0.31). Overall, 23 (39%; 14 on CR1) patients underwent allogeneic stem cell transplant (allo-SCT), with no difference in respect to baseline mutations. The rate of relapse (n = 10; 17%) was also similar with or without ≥ 1 of KIT, RAS, or FLT3 mutations. The presence of any of these 3 mutations was associated with worse relapse free survival (7.7 vs. 12.9 months; p= 0.01), with no significant difference in overall survival (median OS- 94.1 months vs. not reached, p=0.44). Overall, patients with CBF-AML did well independent of induction/consolidation regimen, inclusion of GO, achievement of MRD negativity, or allo-SCT status, with a 2-year OS of > 80%. Mutations in KIT, RAS, and FLT3 are enriched in CBF-AML and contribute to earlier relapse although OS remains favorable across molecular and treatment subgroups.

P503: MRD MONITORING DURING INTENSIVE CHEMOTHERAPY IN PEDIATRIC AML- DATA OF THE AML-BFM GROUP

Background: During the past decades, minimal residual disease (MRD) has been established as a diagnostic tool, providing critical prognostic information in pediatric acute myeloid leukemia (AML). To measure initial treatment response, immunophenotyping was used by most cooperative study groups. However, known limitation of sensitivity and specificity supported the continuous evaluation of qPCR-based MRD detection in pediatric AML. Aims: To determine the prognostic role of MRD monitoring by RT-qPCR in the pediatric AML. Methods: A total of 238 pediatric AML patients were monitored for MRD by reverse-transcriptase quantitative PCR (RT-qPCR) assay from September 2012 to December 2020. Since the inclusion to this study is based on the presence of quantifiable genetic markers, the patient group is strongly biased. The treatment was conducted according to the AML-BFM study 2004 and 2012 as well as the register 12 and 17. All measurements were performed in bone marrow samples or in peripheral blood at initial diagnosis. MRD monitoring included the following aberrations: t(8;21), inv(16), inv(11), NPM1, FLT3-ITD, t(15;17), t(5;11), t(9;11), t(6;9), WT1, t(1;11), t(11;11), t(1;22), t(11;12), t(17;19), t(3;5), t(4;10), t(11;19), t(2;11), t(6;11), t(X;11), t(6;8), t(8;16) and t(8;22). Results: The patients had a mean age at diagnosis of 9.2 years (range 10 days to 18.6 years) and 51 % were females. They were distributed to the following stratification groups: standard risk (56 %), intermediate risk (27 %) and high risk (17 %). The event free survival was 71 % (±3 %) and the OS reached 90 %(±2 %). In core binding factor acute myeloid leukemia (CBF-AML) (n=91) a positive MRD level persists in the majority of cases. Following the 3rd treatment block 64% of cases remained MRD-positive (MRD threshold ≥1x10-5). However, MRD monitoring showed no prognostic relevance as relapses were detected in 18 % (6/33) and 17 % (10/58) of MRD-positive and negative cases, respectively. For patients with NPM1 mutations (n=26) MRD-positivity and -negativity (threshold of ≥1x10-6) showed a similar relapse rate of 10 %. This data are in contrast to reports in adults (Ivey et al. NEJM 2016). In patients with an AML and t(9;11) MRD-positivity after first and second induction indicated a significant higher risk of relapse. After first induction MRD-positive cases (n=19) had a relapse rate of 32 % compared to 13 % for negative cases (n=24). After second induction the relapse rates were 63 % and 22 % for MRD-positive (n=8) and negative (n=27) cases, respectively. Summary/Conclusion: MRD monitoring is a powerful tool to improve risk group stratification in pediatric AML. Despite its high sensitivity and specificity, the prognostic informativeness of MRD monitoring through RT-qPCR varies widely among different genetic subgroups. In CBL-AML or NPM1-positive AML, which are prognostically more favorable, persisting MRD-positivity alone was not associated with an increase in the risk of relapse. In contrast, MRD-positivity in AML with t(9;11) appears to be highly informative. Further studies with larger number of patients are needed to further define AML subgroups and thresholds for MRD-positivity in the pediatric AML.

P575: IMPACT OF MOLECULAR RESPONSE AND CHEMOTHERAPY REGIMEN ON OUTCOMES IN CORE BINDING FACTOR AML

Background: Fludarabine based induction/consolidation regimens result in excellent outcomes in core binding factor acute myeloid leukemia (CBF-AML) Attainment of early polymerase chain reaction (PCR) based optimal minimal residual disease (MRD) responses positively impact long term outcomes and provide early decision timepoints for alternative therapies including stem cell transplantation (SCT). Aims: We studied factors that affected early and late optimal PCR responses (OPR) and survival in patients (pts) of CBF AML who were treated with fludarabine based regiemns (fludarabine, cytarabine and GCSF) with idarubicin (FLAG-IDA) or gemtuzumab (FLAG-GO). Methods: This is a prospective study of pts with N/D CBF-AML treated at our center on FLAG based regimens. Pts received up to 7 cycles of therapy with appropriate dose reductions based on age or toxicity. PCR for the disease defining transcripts (CBFB::MYH11 or RUNX1::RUNX1T1) were monitored after C1, C3 and end of therapy (EOT). Based on our earlier report (Boddu et. al., Leukemia 2018) OPR was defined as PCR transcript <0.1% after C1 and <0.01% for later time points. Results: Between 4/2007 to 12/2019, 174 pts, with a median age of 51 years (range, 19-78) were included. A total of 109 pts (63%) received FLAG-IDA, while the rest got FLAG-GO therapy. This was mostly due to withdrawal of approval of GO in the US for a period of time. Median number of cycles received was 6 (range, 1-7) Baseline parameters are described in Table 1. PCR data is available for 94% pts after C1, 90% after C3 and 92% at EOT. EOT was considered the timepoint at which pt stopped further FLAG based therapy beyond C1. The percent of patients achieving OPR at each time point by regimen are: 68% vs. 41% (p=0.002) after C1, 75% vs. 39% (P< 0.0001) after C3 and 92% vs. 55% (p<0.0001) at EOT for FLAG-GO and FLAG-IDA respectively. On univariate analysis, FLAG-GO regimen favored attainment of post C1 OPR over FLAG-IDA (OR, odds ratio=3.1, 95%CI 1.6-6.2) while age, baseline BM blast, cytogenetic subtype of CBF, ACA and kinase mutations did not. The benefit of FLAG-GO in attaining OPR after C1 was maintained even on a multivariate (MV) model. For EOT OPR, FLAG-GO (OR= 8.5, 95% CI 3.4-26) fared better over FLAG-IDA. Absence of KIT mutation (OR=2.4) and attainment of post C1 OPR (OR= 11.3) were the other relevant factors. On MV analysis, only chemo arm and post C1 OPR remained significant. At a median follow up of 92 months (mos), the RFS was 124 mos and OS not reached (NR) for the whole cohort (RFS 68 mos and OS 102 mos for FLAG-IDA treated pts vs. both NR for FLAG-GO treated pts, p=0.004 and 0.04 respectively). Across the 2 groups there was no difference in RFS or OS between pts who attained early or late OPR. However, on stratifying serial PCR responses with therapy arms, even in pts with early OPR (after C1), RFS was better (NR) in FLAG-GO arm vs 101 mos for FLAG-IDA arm (p= 0.03), though OS was similar, likely reflecting efficacy of salvage therapies in this subset of AML. In a Cox proportional hazards model that included age, therapy arm, kinase mutations, cumulative therapy cycles, post C1 and EOT PCR responses; only younger age and EOT OPR favorably affected RFS; however FLAG-GO treated pts had lower hazards for RFS at any level of PCR response compared to FLAG-IDA treated pts (Fig. 1). Image:Summary/Conclusion: In CBF AML, FLAG-GO regimen leads to higher rate of earlier and end of therapy OPR than FLAG-Ida and substantially better RFS. At any combination of PCR response, FLAG-GO treated patients had lower hazards for relapse than FLAG-IDA treated pts.

PB1812: CORE BINDING FACTOR ACUTE MYELOID LEUKEMIA IN PEDIATRIC POPULATION: THE RESULTS OF A MONOCENTRIC EXPERIENCE

Background: The core binding factor acute myeloid leukemia (CBF-AML) is characterized by t(8;21) and inv(16)(p13q22)/t(16;16)(p13;q22) cytogenetic abnormalities. It is associated with a good prognosis. Aims: In this study, we aimed to assess the treatment outcome of the pediatric CBF- AML in comparison with non CBF-AML treated in our center. Methods: We retrospectively reviewed data of patients under the age of 20 diagnosed with de novo AML in our center during january 2005 and december 2020. The treatment protocol includes: a course of induction (Cytarabine 200mg/m2/day associated with Daunorubicine (DNR) 60 mg/m2/day or Novantrone 12mg/m2/day). If a complete remission (CR) is achieved the chemotherapy is followed by: a cure of ADE (Cytarabin, DNR, Etoposide) associated with 2 cures of high dose of Cytarabine (12g/m2) before 2011 and a cure of ADE associated with 3 cures of high dose of cytarabine (18g/m2) after January 2011. Allogeneic stem cell transplantation (ASCT) from matched sibling donors was limited to patients who are in CR1, having an HLA-identical family donor before January 2011 and for patients who are in CR2 after January 2011. Endpoints were complete remission (CR), overall survival(OS), event free survival (EFS) and relapse rate. Survival statistical analysis performed with Kaplan Meyer method. Results: A total of 52 patients were included, of whom 16 (30%) presented CBF genes. The median age was 10years. The median white blood cells count at diagnostic was 28G/L. Distribution according to the FAB classification was as followed: 1(6%)M1, 8(50%) M2, 6(38%) M4 and 1(6%) M6.the most frequent subgroup was M2 (vs M1 in non CMF-AML, p=0.001). Cytogenetic analysis showed the Inv 16 (p13;q22) in 3 cases (18%) and t(8;21) (q22;q22) were observed in 11 cases (68%). Two patients had both CBFB–MYH11and AML-ETO rearrangement. Six cases (38%) had additional cytogenetic abnormalities. The correlation between cases with and without additional cytogenetic abnormalities did not conclude to any significent difference in terms of CR rate, OS and EFS. We observed a comparatively higher CR rate (87% vs 51% p=0.018) and also a better OS rate (83% vs 35%, p=0.02) at 5 years between CBF-AML and non CBF-AML. In contrast, there was no statisticly significent difference in terms of the EFS (67%vs 62%, p=0.4) and the relapse rate (31% vs 43%, p=0.3) between the 2 groups. Relapse occurred in 5 cases (31%) at a median of 13 months. A second remission was obtained in 2/5 patients. ASCT was performed in only 4 cases (3 after RC1 and 1 after relapse). Summary/Conclusion: The frequency of core binding AML in our study is higher than what has been reported in the literature (30 vs 15%) with predominance of The cytogenetic t(8,21) (68%). The additional cytogenetic abnormalities has no prognostic value. Long term survival in our series compared favorably with results reported by cooperative groups. It can be concluded that ASCT in CR1 for pediatric CBF-AML is no longer indicated.

PB1807: OUTCOME OF CORE BINDING FACTOR ACUTE MYELOID LEUKEMIA IN CHILDREN AND ADOLESCENTS: A SINGLE CENTER EXPERIENCE

Background: Core binding factor acute myeloid leukemia (CBF-AML) is a subgroup of AML, mainly defined by two gene rearrangements affecting CBF;t (8; 21)/RUNX1-RUNX1T1 and inv (16)/CBFB-MYH11. CBF-AML is considered as a favorable cytogenetic group. However, one-third of these patients relapse succeeding treatment. Aims: The main of this study is to evaluate the clinical characteristics and the outcome of this group of patients in our center. Methods: This retrospective study included all CBF-AML diagnosed between 2002 and 2020 in the hematology department of the University Hospital of Sousse. Patients were aged 20 years or less. The diagnosis was confirmed according to the WHO classification of hematological malignancies based on cytology and immune-phenotyping. An initial karyotype during diagnosis was performed in all the cases to classify the cases according to the prognostic MRC classification. Patients were treated by the standard chemotherapy regimen. Promyelocytic leukemia and secondary leukemia were excluded. Statistical analysis was performed using the Kaplan Meier method. Results: Among the 66 children and adolescents diagnosed with AML 15 had CBF AML (23%). 60% were male. The median age was 9 years (3-16). WBC at diagnosis was<4000 in 5 cases, 4000-10000 in 2 cases, between 10000-50000 in 7 cases, and >50000 in 1 case. Disseminated intravascular coagulation was noted in 2 cases. Twelve patients had t(8,21) and 3 patients had inv(16). 75% achieved complete remission after induction. 2 patients had a refractory disease (12,5%). Treatment-related mortality was 12,5% and meantime to relapse was 6,2 months in 5 patients (45%). Three patients responded to salvage chemotherapy (60%) and 2 died (40%). Hematopoietic stem cell transplantation (HSCT) was performed in only 2 patients. For the 3 others, HSCT was not feasible because of the absence of compatible matched related donors. The 5-year overall survival and relapse-free survivals were 55,7% and 58,3% respectively. Summary/Conclusion: Compared to the literature, the frequency of CBF-AML and epidemiological features were very similar. Furthermore, the majority had t (8, 21) in karyotype. Complete remission rate was slightly lower in our study (73% vs 85-96%), Treatment-related mortality was higher (12% vs 3-10%) which may be explained by the absence of protective isolation in the earlier years of the study. Regrettably, PFS was inferior to data from the literature (70-80%). The early use of stem cell transplants could improve our results.