Litzow, Mark R.

Abstract Cytokine receptor–like factor 2 rearrangement (CRLF2r), an aberration causing a Philadelphia chromosome–like gene expression profile and a poor prognostic marker in B-cell acute lymphoblastic leukemia (B-ALL), endows relative chemotherapeutic resistance. Extramedullary disease (EMD), including both central nervous system (CNS) and non-CNS involvement, can also be associated with worse outcomes. The relationship between CRLF2r and EMD is unknown. Based on an initial observation of patients with relapsed/refractory (R/R) CRLF2r B-ALL and EMD, a single-center retrospective review was conducted to evaluate the incidence of EMD in patients with CRLF2r B-ALL. Across 177 children, adolescents, and young adults with R/R B-ALL, 21 (11.9%) harbored CRLF2r, of whom 19 (90.5%) had EMD at some point during their treatment course. In contrast, only 78 of the 156 patients (50%) without CRLF2r ever had EMD (P = .0003). In the CRLF2r cohort, 8 (38.1%) presented with EMD at diagnosis: 7 with CNS and 1 with non-CNS EMD. At relapse, 17 (80.9%) had EMD: 4 (19%) had CNS EMD, 9 (42.9%) had non-CNS EMD, and 4 (19%) had both. Isolated EMD was observed in 2 patients (11.8%) at first relapse and in 3 (17.6%) with multiple relapses. Given these findings, further study to evaluate this potential association between EMD and CRLF2r in R/R B-ALL is indicated.

Abstract TP53 and PPM1D are key regulators of DNA damage response and repair, and somatic mutations in these genes often co-occur in hematopoietic cells, expanding under genotoxic stress. Unlike TP53 mutations, where mechanisms of progression are defined, pathways underlying clonal fitness and transformation in PPM1D mutant cells remain unclear. In collaboration with 5 academic institutions, we analyzed the clinical and molecular landscape of 337 patients with clonal hematopoiesis (CH) and clonal cytopenia of undetermined significance (CCUS) across 4 genotypes: PPM1Dmt/TP53wt (n = 170 [50%]), PPM1Dmt/TP53mt (n = 25 [7%]), TP53mt/PPM1Dwt (n = 17 [5%]), and TP53wt/PPM1Dwt (n = 125 [38%]). All PPM1D variants were truncating, located in exon 6 of the gene, with a median variant allele frequency (VAF) of 6% (range, 0.3%-64%). The PPM1Dmt/TP53mt genotype was most frequently encountered in therapy-related CH/CCUS (t-CH/t-CCUS; 80%, 66.5%, 76.5%, and 19%; P ≤ .001) and had a shorter time interval to detection from last genotoxic exposure (6.2, 5.9, 11.25, and 24.5 months; P ≤ .001) compared with PPM1Dmt/TP53wt, TP53mt/PPM1Dwt, and TP53wt/PPM1Dwt genotypes, respectively. Acknowledging the short follow-up duration, rates of malignant transformation were lower in the PPM1Dmt/TP53wt (2%) and PPM1Dmt/TP53mt (4%) groups compared with PPM1Dwt/TP53wt (12%) and PPM1Dwt/TP53mt (17%) groups (P ≤ .001), respectively. In summary, PPM1D mutations are frequently observed in t-CH/t-CCUS, with low median VAFs, and are associated with low rates of progression, even when comutated with TP53.

Abstract The comparative value of liposomal cytarabine/daunorubicin (CPX-351) versus venetoclax plus a hypomethylating agent (Ven-HMA) in the frontline treatment of older adults with primary ( de novo ) or secondary acute myeloid leukemia (AML) remains uncertain. In the current study, we retrospectively examined outcomes of 600 patients with newly diagnosed AML treated with CPX-351 (N = 112) or Ven-HMA (N = 488). AML subtypes included de novo (46%), post-myelodysplastic syndrome (MDS) (19%), post-myeloproliferative neoplasm (MPN) (12%), post-MDS/MPN (6%), therapy-related (17%) and AML with myelodysplasia-related genetic abnormalities (AML-MR; 46%). Patients receiving CPX-351 were younger (median 65 vs. 73 years; p < 0.01), predominantly female (50% vs. 38%; p = 0.02), more likely to have secondary AML (68% vs. 51%; p < 0.01), and less likely to harbor NPM1 MUT (5% vs. 12%; p = 0.02). Rates of complete response with or without count recovery (CR/CRi) were comparable between CPX-351 and Ven-HMA (55% vs. 60%; p = 0.30), including in AML-MR (60% vs. 63%; p = 0.70). Ven-HMA use was associated with fewer infectious complications (62% vs. 83%; p < 0.01) and yielded higher CR/CRi rates in males (60% vs. 45%; p = 0.04), de novo AML (68% vs. 50%; p = 0.03), and in the presence of STAG2 MUT (86% vs. 44%; p = 0.02), or CEBPA MUT (88% vs. 50%; p = 0.03). Overall survival censored for transplant, was similar (median 10 vs. 13 months; p = 0.90), with Ven-HMA being superior in post-MDS AML (median 12 vs. 7 months; p = 0.02) and CPX-351 in the presence of SF3B1 MUT (not reached vs. 14 months; p < 0.01). Our findings suggest that Ven-HMA is as effective and less toxic than CPX-351 in newly diagnosed AML, including AML-MR, despite selection of younger, fitter patients for CPX-351.

ABSTRACT Background IDH mutations are found in 15%–20% of acute myeloid leukemia (AML). Recent evidence suggests that IDH mutation subtypes may respond differently to intensive chemotherapy. We evaluated blast clearance patterns, remission outcomes, and overall survival (OS) in AML patients with IDH2 R140, IDH2 R172, and IDH1 R132 mutations to assess differences in treatment response. Methods We retrospectively reviewed AML patients diagnosed at Mayo Clinic, Rochester (2016–2023) with NGS data and treated with intensive chemotherapy (7+3 or CPX‐351). Bone marrow blasts were assessed at diagnosis, mid‐induction, and end‐of‐cycle; blast clearance was defined as < 5%. Composite remission (CRc) included CR/CRi per ELN 2022. IDH2 responders were classified as early (after Cycle 1) or late (≥ 2 cycles). Blast reduction was calculated as log 10 (diagnosis blasts/end‐induction blasts) and normalized per day. OS was measured from diagnosis. Results Among 381 patients, 31 had IDH2 mutations (23 R140, 8 R172) and eight had IDH1 R132. Baseline blasts were similar. Mid‐cycle blasts were lower in R140 versus R172 (4% vs. 10%), with higher clearance (68% vs. 38%). End‐induction blasts were lower in R140 versus R172 (2% vs. 4%) with higher clearance (100% vs. 75%). IDH1 and IDH2 showed similar clearance patterns. Log 10 analyses showed deeper and faster blast reduction in R140 versus R172, with comparable kinetics between IDH1 and IDH2 . OS did not differ across subtypes. Early CRc in IDH2 ‐mutated patients was associated with numerically longer OS. Conclusion IDH2 R140 demonstrated faster blast clearance than R172, while remission and survival were similar across IDH subtypes. Trial Registration : The authors have confirmed clinical trial registration is not needed for this submission.

Abstract Introduction Management of acute leukemia (AL) during pregnancy remains challenging. In the first trimester, chemotherapy is toxic to the fetus, while delaying treatment may endanger maternal health, often prompting recommendations for pregnancy termination. In later trimesters, although the risk of congenital malformations decreases, complications such as preterm labor remain prevalent. Delivery prior to chemotherapy may be considered in advanced gestation. This study aimed to describe maternal and fetal outcomes of patients diagnosed with AL during pregnancy. Methods Following institutional review board approval, we retrospectively identified pregnant patients diagnosed with AL between 1995 and 2025 across Mayo Clinic sites (Minnesota, Arizona, Florida). We recorded leukemia subtype, treatment course, maternal and fetal outcomes. Results We identified 18 patients diagnosed with AL during pregnancy, including 11 with acute myeloid leukemia (AML) and 7 with acute lymphoblastic leukemia (ALL). Ten were diagnosed in the first trimester, 3 in the second, and 5 in the third. In the AML group (n=11; median age 30 years, range 18-42), one patient had acute promyelocytic leukemia (APL). ELN 2022 risk stratification was favorable in 5 (45%), intermediate in 4 (36%), and adverse in 2 (18%). In the ALL group (n=7; median age 23 years, range 19-34), 5 had B-ALL (one Philadelphia chromosome-positive) and 2 had T-ALL. All ALL cases were diagnosed in the first trimester. Among first-trimester AMLs, 2 of 3 had core-binding factor (CBF) AML. All eight patients diagnosed in the second and third trimesters had AML (1 APL, 2 CBF AML, 1 KMT2A-rearranged, 1 with DEK::NUP214 fusion, 1 complex karyotype including t(8;21), 2 with normal karyotype). Overall, 15 (83%) patients achieved complete remission (CR) or CR with incomplete count recovery (CRi) after initial induction. One patient had refractory disease and achieved partial remission after salvage, another had refractory disease and achieved CR after multiple lines of therapy, and a third achieved CR after FLAG-idarubicin and revumenib. Five patients received chemotherapy during pregnancy (3 in the first trimester, 1 in the second, 1 in the third); two of these resulted in live births. Among the 10 patients diagnosed in the first trimester, all underwent therapeutic or spontaneous abortion. Of the 3 second-trimester diagnoses, 2 underwent spontaneous or therapeutic abortion at 15 weeks. The third received 7+3 induction at 24 weeks for KMT2A-rearranged AML, followed by preterm delivery at 26 weeks and re-induction with FLAG-idarubicin plus revumenib, achieving CR. Among the 5 third trimester diagnoses, 4 delivered preterm infants (median gestational age 33 weeks) prior to chemotherapy. One patient received 7+3 at 29 weeks and delivered a viable preterm infant at 36 weeks. At a median follow-up of 6.5 years, 5 of 11 patients with AML (45%) and 3 of 7 patients with ALL (43%) died, mostly due to disease progression. Median overall survival was not reached in either group. Causes of death were as follows: 1 of AML, 1 of ALL, 3 of acute stem cell transplant (SCT) complications, 1 of chronic SCT complications, 1 of Hodgkin lymphoma, and 1 of pneumonia. Among patients diagnosed in the second and third trimesters (n=8, all with AML), 6 (75%) resulted in live births: 5 of 5 (100%) third-trimester diagnoses and 1 of 3 (33%) second-trimester diagnoses. All received intensive induction: 7+3 (n=5), 7+3 + ATRA (n=1), 7+3 + gilteritinib (n=1), and 7+3 + nilotinib (n=1). Of the second-trimester group, only one received induction prior to delivery; she later achieved CR with FLAG-ida and revumenib. Among the third-trimester group, one patient received chemotherapy prior to delivery and achieved CR followed by SCT. All but one of the 8 AML patients achieved CR after initial therapy. Conclusions Successful pregnancy outcomes were achieved in 75% of patients diagnosed with AML during the late second or third trimester. Notably, 5 (28%) of patients received chemotherapy during pregnancy. Larger, multi-institutional cohorts are warranted to further characterize the incidence and outcomes of AL in pregnancy.

Abstract Background: MyeloMATCH is an NCI-sponsored initiative for acute myeloid leukemia (AML) and myelodysplastic syndrome (MDS) employing a Master Screening and Reassessment Protocol (MSRP) to assign patients (pts) to a pt and disease biology-specific clinical trial. Several trials evaluating initial therapies are currently open, while subsequent trials dedicated to eradicating measurable residual disease during consolidation and including stem cell transplant are being developed. A pt enrolled at diagnosis may be followed longitudinally and be eligible for trials in sequential tiers throughout the treatment course. We report key data concerning the first cohort of pts enrolled on the MSRP. Methods: After pts with suspected AML or MDS consent for the MSRP, blood and marrow are sent to the myeloMATCH Molecular Diagnostics Network (MDNet) of central CLIA labs operating under a single Investigational Device Exemption to rapidly define molecular, cytogenetic, and immunophenotypic characteristics. These data are catalogued by a bioinformatics team (MATCHBox) and reviewed daily to assign participants to an available trial based on pt and disease features. A Tier Advancement Pathway (TAP) allows standard of care therapy with potential for assignment to subsequent myeloMATCH trials. Since activation in May 2024, 550 patients age≥18 were enrolled on the MSRP from 76 institutions: 48 Academic, 14 NCORP, 11 community, 3 VA. There are currently 4 open randomized AML trials (≥age 60 or unfit with mutant FLT3, ≥age 60 IDH2 mutant AML, fit age&lt;60 ELN 2017 intermediate-risk AML, fit age&lt;60 ELN 2017 adverse risk) and 1 MDS trial(IDH2 mutant). Patients not eligible for an open protocol were assigned to TAP. Results: Of the 550 pts consented, 491 completed screening assays; 49 had no or incomplete samples; 10 withdrew before completed analysis. Median cytogenetic turnaround time (TAT) was 69 hours (91% within 72 hours), and median Next Generation Sequencing (NGS) TAT from receipt was 49 hours (95% within 72 hours). Seventy-six pts (of 491 with assay data) were not assigned due to non-AML or non-MDS diagnoses, the most common being: B-ALL [n=11], MPN [9], benign marrow [9], APML [7], and MPAL [6]. The AML/MDS verified cohort was 415 pts, 366 (89.2%) patients with AML (45% age &lt;60) and 49 (11.8%) with MDS. The median age at screening was 63 years (range:18-95) and 186 (45%) were female. Eighty-two percent identified as White, 7.5% Black, 3% Asian, 7% unknown, and 9% as Hispanic. The most frequent mutations in the AML pts were NPM1 (24.0%), DNMT3A (22.7%), TET2 (19.9%), NRAS (18.0%), FLT3 (18.0% ITD, TKD 7.1%), TP53 (14.5%), and CEBPA (8.7%); IDH1/2 mutation rates were 8.2% and 13.7%, respectively. Co-mutations include FLT3/NPM1 (9.8%), NPM1/IDH2 (4.4%), IDH1/2 and any RAS (3.8%). Karyotypes were normal in 40.4%, complex 20.8%, inv(16) 6.0%, MLL/KMT2A 4.6% and t(8;21) 1.9%. 29% had favorable risk disease, 29% intermediate, and 42% adverse (ELN 2017). In MDS, mutations included: TP53 (36.7%), RUNX1 (20.4%) ASXL1 (20.4%), TET2 (18.4%), spliceosome mutations (SRSF2, SF3B1, U2AF1 and ZRSR2, 28.6%) andIDH1/2 in 4.1% and 6.1%, respectively. Karyotypes were normal in 24.5%; complex in 40.8%. By IPSS-R, 2.4% were low, 73.8% intermediate, 2.4% high, and 21.4% very high risk. 82/415 (20%) pts were assigned to initial therapy protocol, with an increase in assignment rate to 44% in the most recent two months. 71/415 pts (16%) were enrolled in one of the MyeloMATCH studies. Three-hundred forty-four pts (80%) were assigned and enrolled to TAP (296 AML, 48 MDS) for potential assignment to subsequent tier trials. In the TAP AML pts, 99 (33%) have completed initial treatment, including intensive chemotherapy (IC) in 62% of pts and hypomethylating agents/venetoclax (HMA/VEN) in 38%. In pts &lt;60 years of age, 87% received IC v. 13% with HMA/VEN, in &gt;60 34% IC v. 66% HMA/VEN and in age 60-75 42% IC v. 58% HMA/Ven. Conclusion: MyeloMATCH has screened over 500 pts from academic and community sites in the US and Canada in 14 months, meeting the TAT goal of sample acquisition to results of &lt;72 hours. Assignment to treatment protocols has substantially increased recently. As additional trials open (12 in development) we expect the percentage of pts enrolled on MSRP who go on to therapeutic trials will markedly increase, thereby allowing a personalized medicine approach for a broad group of US and Canadian adult pts with AML and MDS.

Abstract Introduction: Clinical outcomes for patients (pts) with Philadelphia chromosome positive (Ph+) B-cell precursor Acute Lymphoblastic Leukemia (B-ALL) have significantly improved with the incorporation of tyrosine kinase inhibitors (TKI) and immunotherapy. Although the incidence of central nervous system (CNS) relapse in Ph+ B-ALL is rare, it has become an emerging challenge with chemotherapy-free approaches. While IKZF1, CDKN2A/B and emergence of T315I kinase domain mutations in ABL1 have been associated with worse outcomes (Foà R, JCO, 2024),further characterization of patients with CNS relapse could prove useful in risk stratification and optimizing treatment intensification. Currently, high white blood cell count (WBC) is being assessed as a marker to identify pts who may benefit from addition of CNS penetrant chemotherapy (ex. cytarabine or high-dose methotrexate (HD-MTX)) to TKI and immunotherapy protocols (Short NJ, J Hematol Oncol, 2025). Methods This is a multicenter retrospective study of relapsed/refractory Ph+ B-ALL pts under the COMMAND consortium. Age, gender, induction regimen and TKI of choice during induction were descriptively reported for the entire cohort. Categorical variables were compared, using Fisher's exact test, between pts with CNS relapse and pts with systemic relapse. Variables of interest were the presence of IKZF1 or CDKN2A/B alterations, emergence of T3151 mutation, CNS disease at diagnosis (dx), WBC &gt;70K/microliter at dx, use of high-dose methotrexate (HD-MTX) during induction or consolidation, and use of TKI as part of the induction regimen. Odds ratio (OR) and 95% confidence intervals (CI) were reported for each variable. Results A total of 654 Ph+ B-ALL pts were initially identified across multiple centers in the United States, of whom 20 (3%) experienced a CNS relapse and 157 (24%) experienced a systemic relapse on median follow up of 29 months (range, 0-207). A total of 15 pts with CNS relapse and 114 pts with systemic relapse were used for this analysis after exclusion of pts without molecular data. The median age for the 129 pt cohort was 55 years (range 22-85), of whom 65 pts (50%) were male. Induction regimens used were intensive chemotherapy (IC)+TKI for 79 pts (61%), low-intensity chemotherapy or steroids (LDC-S)+TKI for 40 pts (31%), IC without TKI during induction for 5 pts (4%) and blinatumomab+TKI for 1 pt (1%). TKI of choice during induction included second-generation TKIs (dasatinib, nilotinib) for 77 pts (60%), imatinib for 30 pts (23%), ponatinib for 15 pts (12%) and none during induction for 5 pts (4%). CNS disease at dx was found in 6/15 pts (40%) with CNS relapse and 9/114 pts (8%) with systemic relapse, which was a statistically significant difference (p=0.002, OR= 7.57, 95% CI= 1.81 - 31.08). The systemic treatment regimens for the 15 pts with CNS disease at x were IC+TKI for 10 pts (66%) and LDC-S+TKI for 5 pts (33%), 9 of the pts (60%) received HD-MTX during induction. Intrathecal (IT) chemotherapy administration data at dx was available for 8 pts (53%) with CNS disease at dx, of whom 2 pts received &lt;9 doses, 4 pts received 9-12 doses and 2 pts received &gt;12 doses of IT chemotherapy. Although not statistically significant, pts with CNS relapse were more likely to have IKZF1 or CDKN2A/B alterations (p = 0.648, OR= 1.44, 95% CI= 0.14-7.78), WBC &gt;70K/mcl (p = 0.472, OR= 1.73, 95% CI= 0.34-7.41), emergence of T3151 mutations (p = 0.123, OR= 2.54, 95% CI= 0.72-8.84) and use of HD-MTX during induction or consolidation (p = 0.262, OR= 2.15, 95% CI= 0.61-8.61); while they were less likely to have received a TKI during induction (p = 0.106, OR= 0.18, 95% CI= 0.02-2.34). Conclusion This data confirms that the presence of CNS disease at dx is associated with CNS relapse. Despite recent incorporation into clinical trials, WBC≥70K/mcl and omission of HD-MTX were not seen more frequently in pts with CNS relapse in this cohort. However, this analysis is limited by the small number of pts who experienced CNS relapse. With the rising use of chemotherapy-free regimens, prospectively trialing treatment intensification, such as with additional IT chemotherapy or HD-MTX, could be prospectively trialed in pts with CNS disease at dx to potentially improve outcomes for this subset of pts. The impact of increasing IT chemotherapy doses or additional cycles of systemic chemotherapy in this pt population is yet to be elucidated.

Abstract Venetoclax (Ven) in combination with hypomethylating agents (HMA) is widely used as frontline treatment in older or unfit patients with acute myeloid leukemia (AML). Liposomal cytarabine and daunorubicin (CPX-351) is FDA-approved for the treatment of secondary AML, including therapy-related (t-AML) and AML with myelodysplasia-related changes (AML-MR). The current study aimed to provide a comprehensive comparison between the two treatment strategies to better inform clinical decisions. Methods The current retrospective analysis was performed under an institutional review board approved minimal risk protocol at Mayo Clinic (MN, AZ, FL). AML-MR gene mutations or cytogenetic abnormalities were categorized according to the International Consensus Classification (Arber et al. Blood 2022;140:1200). Treatment response was assessed according to the 2022 European LeukemiaNet (ELN) criteria (Dohner et al. Blood 2022;140:1345). Overall survival (OS) analysis was censored for allogeneic stem cell transplant (ASCT). Statistical analyses were performed using JMP Pro (Version 18.0.0). Results A total of 600 patients with newly diagnosed AML (ND-AML) treated with CPX-351 (N-112, 19%), or Ven-HMA (N=488, 81%) were included. AML subtypes included de novo (N=277, 46%), post-myelodysplastic syndrome (post-MDS, N=114,19%), post-myeloproliferative neoplasm (post-MPN, N=70, 12%), post-MDS/MPN (N=36, 6%), t-AML (N=103, 17%) and AML-MR (N=274, 46%). Compared with those treated with Ven-HMA, patients receiving CPX-351 were younger (median age 65 vs 73 years; p&lt;0.01), more likely to be female (50% vs 38%; p=0.02), more frequently diagnosed withsecondaryAML (68% vs 51%; p&lt;0.01), and less likely to have NPM1MUT (5% vs 12%; p=0.02) whereas ELN 2022 cytogenetic risk distribution was similar between the two (adverse risk; 43% vs 40%; p=0.5). Comparison of treatment response and survival Complete response rates with (CR) or without (CRi) count recovery were similar between CPX-351 and Ven-HMA overall (55% vs 60%) as well as specifically in patients with AML-MR (60% vs 63%), adverse karyotype (44% vs 44%), NPM1MUT (100% vs 89%), TP53MUT(32% vs 45%), IDH1MUT (60% vs 76%), IDH2MUT (63% vs 77%), SF3B1MUT(71% vs 45%), and CBLMUT (33% vs 69%) [p&gt;0.05 in all instances]. Compared to those with CPX-351, CR/CRi rates with Ven-HMA were superior in males (60% vs. 45%; p=0.04) and in patients with de novo AML (68% vs. 50%; p=0.03), STAG2MUT (86% vs. 44%; p=0.02), or CEBPAMUT (88% vs. 50%; p=0.03); infectious complications were significantly more frequent with CPX-351 (83% vs 62%, p&lt;0.01). At a median follow-up of 12 months (range; 1-88), 416 (69%) deaths, 179 relapses (44% in CPX-351 and 52% in Ven-HMA responders) and 149 ASCTs (53% in CPX-351 and 18% in Ven-HMA) were documented. OS rates were similar between CPX-351 and Ven-HMA, in general (median 10 vs 13 months), as well as in patients with adverse karyotype, TP53MUT, IDH1MUT, and IDH2MUT (p&gt;0.05 in all instances). By contrast, OS was superior in Ven-HMA-treated patients with post-MDS AML (median 12 vs. 7 months; age-adjusted p=0.02) and in CPX-351-treated patients harboring SF3B1MUT(median not reached vs 14 months; age-adjusted p&lt;0.01). In addition, a borderline-significant OS advantage for CPX-351 was apparent in patients with PTPN11MUT (13.5 vs 8 months; p=0.08). Comparison in ICC defined AML-myelodysplasia-related CR/CRi and OS rates were comparable between patients treated with CPX-351 (N=57) or Ven-HMA (N=217), with response rates of 60% vs 63% (p=0.68) and median OS of 10 vs 14 months (p=0.61), respectively. However, OS was superior with Ven-HMA in patients with post-MDS AML (15 vs 8 months; age-adjusted p=0.02) and with CPX-351 in those with SF3B1MUT (NR vs 14 months; age-adjusted p=0.02). Conclusions: The current study suggests that Ven-HMA was as effective and possibly less toxic than CPX-351 for the treatment of ND-AML, including AML-MR, despite the bias for younger and fitter patients treated with the latter regimen. Observed differences involving patients with SF3B1MUT or post-MDS AML require validation in prospective studies and provide parameters for developing treatment-specific predictive models that will be presented at the meeting.

Abstract Introduction:A comprehensive integration of significantly mutated genes and pathways with molecular subgroups is lacking in adult B-ALL. Furthermore, the genomic drivers underlying each subgroup remain to be identified.We aimed to perform genomic analysis on a large cohort of patients with adult B-ALL, and to correlate genomic markers with achievement of MRD negativity enabling blinatumomab randomization, and with subsequent response to blinatumomab. Methods:For genomic analysis, we studied 569 adults with newly diagnosed B-ALL registered for initial screening on the ECOG-ACRIN-led E1910 trial (NCT02003222), which evaluated the addition of blinatumomab to standard consolidation chemotherapy. The median age was 52 yrs (range 30 to 71 yrs), with 52% males. Analysis was performed on tumor and matched-normal samples using whole transcriptome sequencing (RNA-seq; tumor only; n=569), whole exome sequencing (n=490), whole genome sequencing (n=131), and single nucleotide polymorphism array (n=445). B-ALL cases were classified into 22 molecular groups. Outcome analysis was limited to patients enrolled and treated on E1910 (n=319). Results: Driver genes (n=268) were identified by the mutation-significance detection tool dNdScv or by the presence of pathogenic variants in known cancer genes, with NUP188 identified as a novel driver gene. Recurrently mutated pathways included: B-cell development (46%), cell cycle (44%), epigenetic regulation (30%), other transcriptional regulation (27%), Ras signaling (25%), RNA machinery (17%) and JAK-STAT signaling (8%). A high frequency of high-risk subtypes was observed including BCR::ABL1 (20%), BCR::ABL1-like (18%), low hypodiploid (14%) and KMT2A (12%). Using tSNE analysis, we identified a new cluster of cases (n=20, 3.5%) lacking a known subgroup driver, with overexpression of CEBPA (n=13) or CEBPB (n=7), distinct from CEBPE/ZEB2, termed “CEBP-altered” ALL (CEBPalt). Five of 13 cases with high CEBPA expression harbored an IGH::CEBPA rearrangement and one harbored a RXRA::CEBPA enhancer hijacking alteration. Of the 7 cases with high CEBPB expression, 5 harbored IGH::CEBPB, and two of these had concomitant clonal BCR::ABL1 fusions. To identify additional mechanisms of CEBP deregulation, in situ Hi-C coupled to H3K27 acetylation immunoprecipitation (HiChIP) was performed on 5 cases. Four cases showed evidence of de novo CEBPA enhancer activity. In two cases, we identified novel insertions (12 and 34nt) ~2kb downstream of CEBPA. A novel translocation and enhancer hijacking event between LINC00426 and the 5' UTR of CEBPB was identified in the remaining case. Overall, we confirmed genomic alterations of CEBPA or CEBPB in 16 of 20 cases with available material. Thus, we have identified a new molecular subgroup of adult B-ALL characterized by genomic alterations that drive enhancer hijacking and oncogenic deregulation of CEBPA/CEBPB. Several subgroups were enriched in patients that failed induction chemotherapy (n=62) or were MRD-positive (n=63) compared to those that achieved MRD-negative status (n=194): BCR::ABL1-like (30 vs 14%, p&lt;0.001), KMT2A (18 vs 9%, p=0.03) and BCL2/MYC (5 vs 1%, p=0.06). Conversely, the following subgroups were enriched in patients that achieved MRD-negativity: PAX5alt (6 vs 18%, p=0.002), TCF3::PBX1 (0 vs 5%, p=0.01) and ZNF384 (2 vs 6%, p=0.08) Within each molecular subgroup we compared the survival of patients who achieved MRD-negative status after induction and were randomized to receive blinatumomab plus chemotherapy (n=93) or chemotherapy only (n=91). Although numbers were low, blinatumomab improved relapse-free survival for patients with hyperdiploid, PAX5alt, BCR::ABL1-like and KMT2A ALL compared to chemotherapy alone. Clonal hematopoiesis of indeterminate potential (CHIP)-related gene mutations were identified in 121 of 417 cases analyzed (29% total: somatic 74%, remission 31%, both 5%). TP53 mutations were most frequent (n=65 patients), with the majority identified in patients with low hypodiploid (n=52). Interestingly, patients with CRLF2 rearrangements collectively harbored the highest number of other CHIP gene mutations (n=13), including DNMT3A (n=4), TET2 (n=3) and ASXL1 (n=3). Conclusions:We provide a comprehensive landscape of genomic alterations in adult B-ALL and identify a new group characterized by deregulation of CEBPA/CEBPB (CEBPalt). We also provide insights into the efficacy of blinatumomab in different molecular subgroups of adult B-ALL.