Harvey, Richard C.

Abstract Introduction Ph-like B-ALL is a poor-risk B-ALL subtype defined by gene expression signatures that resemble the BCR::ABL1-associated transcriptional program in the absence of the BCR-ABL1 oncoprotein. Recent studies have demonstrated that up to 80% of Ph-like B-ALLs have recurrent gene fusions involving cytokine receptors or tyrosine kinases that can be identified via cytogenetics, fluorescence in situ hybridization (FISH) or RNA sequencing. However, the inability to rapidly and accurately identify these alterations in the clinical setting is a major impediment to developing therapeutic strategies that may have efficacy in this B-ALL subtype. Here we used 88 patient (pt) samples to validate a rapid, streamlined clinical WGS assay (ChromoSeq) for B-ALL and assessed the diagnostic yield for Ph-like-associated SVs in 136 pts enrolled in the Alliance A041501 clinical trial. Methods ChromoSeq is a clinical WGS assay for hematologic malignancies that uses rapid laboratory workflows and focused analysis methods to identify clinically relevant SVs, copy number alterations and gene-level mutations. We updated the ChromoSeq pipeline for use in B-ALL pts and validated it using 88 retrospective B-ALL samples (80 adult/young adult and 8 pediatric from Washington University School of Medicine and St. Louis Children's Hospital), 54 of which were analyzed via RNAseq for gene fusions and a 6-gene Ph-like B-ALL signature (CA6, SPATS2L, MUC4, JCHAIN, BMPR1B, ADGRF1, NRXN3 and CRLF2). The “ChromoSeqV2” assay was then used to analyze 136 pretreatment blood or bone marrow samples from the Alliance A041501 (trial NCT03150693). These results were compared to data from RNAseq obtained for research purposes (N=35), clinical cytogenetics (N=69) and Ph-like classification via low-density microarray (LDA) card analysis (all pts). Results ChromoSeqV2 was validated in a CLIA-licensed setting using cohort of 88 retrospective B-ALL samples, 45 of which had ICC and WHO class-defining SVs based on G-banded karyotyping, FISH or RNAseq. ChromoSeqV2 detected 100% of the non-Ph-like SVs (37/37), including BCR::ABL1 (N=20), KMT2Ar (N=9), ETV6::RUNX1 (N=3), TCF3::PBX1 (N=1), and rearrangements involving MYC (N=2) or MEF2D (N=2). Fifteen patients met criteria for Ph-like B-ALL via cytogenetics or RNAseq either due to rearrangements of CRLF2 (N=5), JAK2 (N=2) or ABL2 (N=1) or high expression of a 6-gene Ph-like signature (N=7). ChromoSeqV2 detected a Ph-like SV in 93% of these cases (14/15) with 100% specificity in samples negative by RNAseq (N=23). ChromoSeqV2 was then used to profile 136 samples from the Alliance A041501 trial, where it identified ICC and WHO class-defining SVs in 87 pts (64%; 95% CI: 55-72%), including Ph-like SVs (56/136, 41%), KMT2A rearrangements (N=5), TCF3::PBX1 (N=3) and SVs involving MYC (N=3), MEF2D (N=2), DUX4 (N=2), and ZNF384 (N=1). Ph-like SVs were dominated by CRLF2 rearrangements (N=45) and included SVs involving EPOR (N=4), JAK2 (N=3), ABL1/ABL2 (N=2) and PDGFRB (N=1). IGH was the most common CRLF2 partner (N=32), followed by P2RY8::CRLF2 (N=7) and other genes (N=5). Multiple CRLF2 SVs were detected in 4 pts, and 33% (15/45) of pts with a CRLF2 rearrangement had a co-occurring CRLF2 gene mutation. The yield of ChromoSeqV2 for SVs in pts with the Ph-like expression signature via LDA card analysis was 66% (54/82; 95% CI 55%-76%) compared to 24% (11/45; 95% CI 13%-40%) by cytogenetics when these studies were successful and 70% (12/17; 95% CI 44%-90%) vs RNAseq in pts with available data. The sensitivity of ChromoSeqV2 for Ph-like SVs identified by either cytogenetics, FISH or RNAseq was 100% (21/21; 95% CI 84%-100%) and the positive predictive value of Ph-like SVs for the Ph-like expression signature by the LDA card assay was 96% (54/56; 95% CI 88%-99%). Conclusions Genomic assessment of 136 B-ALL pts from the Alliance A041501 trial using the ChromoSeqV2 rapid clinical WGS assay was 100% sensitive for Ph-like SVs identified by other molecular methods and had a 96% PPV for the Ph-like expression signature via LDA card analysis. The diagnostic yield of SV pts with the Ph-like signature was 66% using ChromoSeqV2, which was similar to RNAseq and superior to cytogenetics. These results demonstrate that ChromoSeqV2 is an effective approach for identifying potentially targetable rearrangements in B-ALL pts suspected of having the Ph-like phenotype. Support: U10CA180821, U10CA180882; . Servier; Pfizer.

Introduction: Inotuzumab ozogamicin (INO) is an antibody targeting CD22 conjugated with a cytotoxic antitumor antibiotic (calicheamicin) approved for treatment of relapsed/refractory CD22 positive B-cell acute lymphoblastic leukemia (ALL) (Kantarjian et al. NEJM 2017). CD22 is expressed on the surface of lymphoblasts in ALL (~95%). Young adult patients (pts) 18-39 years (yrs) treated on the pediatric regimen CALGB 10403 resulted in a 3-yr event-free survival (EFS) of 59% (95% CI: 52-67%) and an estimated 3-yr overall survival (OS) of 73% (95% CI: 68-78%) (Stock et al. Blood 2019). Alliance A041501(NCT03150693), a phase 3 NCTN sponsored cooperative group trial was conducted to determine if the addition of INO to the CALGB 10403 pediatric regimen would significantly improve EFS. Methods: Eligibility included pts 18-39 years with newly diagnosed CD22 positive ALL, defined as baseline expression in > 20% of lymphoblasts by local institution. Pts with Burkitt-type ALL, BCR::ABL1 positive ALL, or Down syndrome were excluded. Eligible pts received the CALGB 10403 regimen modified to omit extended induction, include dexamethasone as opposed to prednisone as steroid backbone, cap the pegaspargase dose to 3750 units, and adding rituximab for pts with CD20 expression (> 20%). An amendment added blinatumomab for minimal residual disease (MRD) positivity. Pts achieving a complete remission (CR/CRi) or partial remission (PR) were eligible for randomization. Following a 6 pt safety run-in with INO, pts were randomized 1:1 to receive INO or continue CALGB 10403 backbone. Two cycles of INO (1.5 mg/m2/cycle) were administered following induction in the experimental arm. Pts were stratified by age, disease status post induction (M0/M1 vs M2), CD20 status, and LDA Card, which tests for the Ph-like status. The primary endpoint was to determine if the addition of INO would improve the EFS of the pediatric regimen CALGB 10403 without censoring for stem cell transplant (SCT). Key secondary endpoints included the impact of INO on disease-free survival (DFS), OS, and MRD. The Alliance Data and Safety Monitoring Board halted enrollment after 273 out of a planned 341 pts were registered because of increased grade (gr) 5 events in the INO arm compared with the control arm. Results: 273 pts were enrolled between 6/15/2018, and 5/24/2022. Median age was 27.0 yrs, 65.2% were White, 30.4% were Hispanic, and 63.4% were male. Baseline CSF analysis revealed 14% with CNS-2/3 disease. The overall CR rate was 86.8% (82.8-90.8%). 46 pts were not randomized due to death (5), withdrawal (6), ineligibility (3), toxicity (5), receipt of non-protocol therapy (8), progression (5), and other (14). 227 eligible pts were randomized 1:1 to receive INO (N=111) or not (N=116)). For randomized pts, 92.5% achieved M0/M1 marrow status, 48.9% had a positive LDA Card defining Ph-like ALL, 50.7% were CD20 positive. Only 36 pts (13%) received a SCT. With a median follow up of 28.3 months for randomized pts, 3-yr EFS was 69.0% (59.1-80.5%) for the INO arm and 66.7% (57.1-78.1%) for the control (HR=0.97; 0.58-1.63). Similarly, the 3-yr OS was 79.4% (71.0-88.7%) for the INO arm and 80.3% (71.9-89.6%) for the control (HR=1.05; 0.55-2.01). The MRD undetectable rate at Course II Day 56 was 80.6% in the INO arm and 74.2% in the control arm. Univariate analysis suggests improved EFS with INO in pts with a positive LDA card (Ph-like ALL) and of Hispanic ethnicity. There were 22 gr 5 events, 7 occurred prior to randomization. Of the 15 gr 5 events on the randomized cohort, 12 were reported in the INO arm and 3 in the control arm. Of the 12 gr 5 events in the INO arm, all occurred during intensive consolidation courses complicated by prolonged pancytopenia infection/sepsis (8), hepato-biliary in setting of infection (2), multi-organ failure (1), or post-surgical complication (1). These events occurred after INO during Course II (3), Course III (5), or Course IV (4). Conclusions: Although this trial did not meet the primary EFS endpoint for the addition of INO to the pediatric regimen CALGB 10403, these data provide compelling evidence for continued use of pediatric regimens in young adults with ALL as the EFS and OS compares favorably with prior published results. INO may still be efficacious if late toxicity can be mitigated. A pilot study is planned that will decrease INO dose, add 2 cycles of blinatumomab and strict infectious prophylaxis guidelines. Support: U10CA180821, U10CA180882

PURPOSE Although cure rates for childhood acute lymphoblastic leukemia (ALL) exceed 90%, ALL remains a leading cause of cancer death in children. Half of relapses arise in children initially classified with standard-risk (SR) disease. MATERIALS AND METHODS To identify genomic determinants of relapse in children with SR ALL, we performed genome and transcriptome sequencing of diagnostic and remission samples of children with SR (n = 1,381) or high-risk B-ALL with favorable cytogenetic features (n = 115) enrolled on Children's Oncology Group trials. We used a case-control study design analyzing 439 patients who relapsed and 1,057 who remained in complete remission for at least 5 years. RESULTS Genomic subtype was associated with relapse, which occurred in approximately 50% of cases of PAX5 -altered ALL (odds ratio [OR], 3.31 [95% CI, 2.17 to 5.03]; P = 3.18 × 10 –8 ). Within high-hyperdiploid ALL, gain of chromosome 10 with disomy of chromosome 7 was associated with favorable outcome (OR, 0.27 [95% CI, 0.17 to 0.42]; P = 8.02 × 10 –10 ; St Jude Children's Research Hospital validation cohort: OR, 0.22 [95% CI, 0.05 to 0.80]; P = .009), and disomy of chromosomes 10 and 17 with gain of chromosome 6 was associated with relapse (OR, 7.16 [95% CI, 2.63 to 21.51]; P = 2.19 × 10 –5 ; validation cohort: OR, 21.32 [95% CI, 3.62 to 119.30]; P = .0004). Genomic alterations were associated with relapse in a subtype-dependent manner, including alterations of INO80 in ETV6::RUNX1 ALL, IKZF1 , and CREBBP in high-hyperdiploid ALL and FHIT in BCR::ABL1 -like ALL. Genomic alterations were also associated with the presence of minimal residual disease, including NRAS and CREBBP in high-hyperdiploid ALL. CONCLUSION Genetic subtype, patterns of aneuploidy, and secondary genomic alterations determine risk of relapse in childhood ALL. Comprehensive genomic analysis is required for optimal risk stratification.

Background: Approximately 2-3% of B-ALL patients have Philadelphia chromosome like (Ph-like) B-ALL with an ABL-class fusion ( ABL1, ABL2, PDGFRB, or CSF1R fusions), but lacking BCR::ABL1. These patients are predicted to be sensitive to ABL-class tyrosine kinase inhibitors, such as imatinib or dasatinib. Ph-like B-ALL is associated with male sex, older age, higher initial white blood cell (WBC) count, elevated end of induction (EOI) minimal residual disease (MRD), and poor outcome. The AALL1131 Dasatinib arm was designed to evaluate response to therapy following induction of patients with ABL-class fusion B-ALL, when given dasatinib continuously on a modified Berlin-Frankfurt-Münster (MBFM) backbone. Methods: Between February 2012 and March 2019, AALL1131 enrolled patients 1-30 years with newly diagnosed high risk (HR) B-ALL. AALL1131 was amended in August 2016, to include the Dasatinib arm for patients with ABL-class fusions involving ABL1, ABL2, PDGFRB, and CSF1R. Patients with Down Syndrome were not eligible for the Dasatinib arm. ABL-class fusion B-ALL patients with a predicted TKI-sensitive mutation were screened by low density array (LDA) PCR and confirmed by additional molecular testing. Following 4-drug induction, patients with HR B-ALL and ABL-class fusions received MBFM with dasatinib (60 mg/m 2, maximum 140 mg) daily from start of consolidation through end of maintenance. Dasatinib was held only for toxicity. Results: Twenty-two evaluable patients with HR B-ALL were non-randomly assigned to the Dasatinib arm. ABL-class 3' partners included ABL1 (n=4), ABL2 (n=4), PDGFRB (n=12), and CSF1R (n=2). Compared to all patients on AALL1131, patients treated on the Dasatinib arm were older (median age at diagnosis 14 versus 10 years, p=0.008), more often male (77% versus 56%, p=0.046), and had a trend towards an increased initial WBC (median WBC at diagnosis 44,000/µL versus 19,000/µL, p=0.086). Patients with ABL-class fusions had EOI MRD > 0.01% in 20 of 22 patients and available end of consolidation MRD >0.01% in 6 of 10 patients. Only 5 of 22 (22.7%) patients completed prescribed protocol therapy. Reasons for therapy discontinuation included induction failure (n=2), relapse (n=1), alternate therapy (n=1), determined to be in the patient's best interest (n=10), death (n=1), unknown (n=2). Compared to all patients on AALL1131, four-year disease-free survival was 52.5+18.1% versus 86.8+0.7% (p<0.0001) and overall survival 79.4+13.6% versus 89.2+0.4% (p<0.0001). Dasatinib was well tolerated with no unexpected treatment related toxicities. Conclusion: Patients with ABL-class fusions were more likely male, EOI MRD+, and had poorer outcomes. Seventy-seven percent of patients enrolled on the Dasatinib arm did not complete prescribed therapy. While dasatinib was well tolerated, treatment failures occurred early, indicating alternate strategies are needed.

PURPOSE Patients with Down syndrome (DS) and B-ALL experience increased rates of relapse, toxicity, and death. We report results for patients with DS B-ALL enrolled on Children's Oncology Group trials between 2003 and 2019. METHODS We analyzed data for DS (n = 743) and non-DS (n = 20,067) patients age 1-30 years on four B-ALL standard-risk (SR) and high-risk trials. RESULTS Patients with DS exhibited more frequent minimal residual disease (MRD) ≥0.01% at end induction (30.8% v 21.5%; P < .001). This difference persisted at end consolidation only in National Cancer Institute (NCI) high-risk patients (34.0% v 11.7%; P < .0001). Five-year event-free survival (EFS) and overall survival (OS) were significantly poorer for DS versus non-DS patients overall (EFS, 79.2% ± 1.6% v 87.5% ± 0.3%; P < .0001; OS, 86.8% ± 1.4% v 93.6% ± 0.2%; P < .0001), and within NCI SR and high-risk subgroups. Multivariable Cox regression analysis of the DS cohort for risk factors associated with inferior EFS identified age >10 years, white blood count >50 × 103/μL, and end-induction MRD ≥0.01%, but not cytogenetics or CRLF2 overexpression. Patients with DS demonstrated higher 5-year cumulative incidence of relapse (11.5% ± 1.2% v 9.1% ± 0.2%; P = .0008), death in remission (4.9% ± 0.8% v 1.7% ± 0.1%; P < .0001), and induction death (3.4% v 0.8%; P < .0001). Mucositis, infections, and hyperglycemia were significantly more frequent in all patients with DS, while seizures were more frequent in patients with DS on high-risk trials (4.1% v 1.8%; P = .005). CONCLUSION Patients with DS-ALL exhibit an increased rate of relapse and particularly of treatment-related mortality. Novel, less-toxic therapeutic strategies are needed to improve outcomes.

Abstract Genomic classification has improved risk assignment of pediatric, but not adult B-lineage acute lymphoblastic leukemia (B-ALL). The international UKALLXII/ECOG-ACRIN E2993 (#NCT00002514) trial accrued 1229 adolescent/adult patients with BCR-ABL1− B-ALL (aged 14 to 65 years). Although 93% of patients achieved remission, 41% relapsed at a median of 13 months (range, 28 days to 12 years). Five-year overall survival (OS) was 42% (95% confidence interval, 39, 44). Transcriptome sequencing, gene expression profiling, cytogenetics, and fusion polymerase chain reaction enabled genomic subtyping of 282 patient samples, of which 264 were eligible for trial, accounting for 64.5% of E2993 patients. Among patients with outcome data, 29.5% with favorable outcomes (5-year OS 65% to 80%) were deemed standard risk (DUX4-rearranged [9.2%], ETV6-RUNX1/-like [2.3%], TCF3-PBX1 [6.9%], PAX5 P80R [4.1%], high-hyperdiploid [6.9%]); 50.2% had high-risk genotypes with 5-year OS of 0% to 27% (Ph-like [21.2%], KMT2A-AFF1 [12%], low-hypodiploid/near-haploid [14.3%], BCL2/MYC-rearranged [2.8%]); 20.3% had intermediate-risk genotypes with 5-year OS of 33% to 45% (PAX5alt [12.4%], ZNF384/-like [5.1%], MEF2D-rearranged [2.8%]). IKZF1 alterations occurred in 86% of Ph-like, and TP53 mutations in patients who were low-hypodiploid (54%) and BCL2/MYC-rearranged (33%) but were not independently associated with outcome. Of patients considered high risk based on presenting age and white blood cell count, 40% harbored subtype-defining genetic alterations associated with standard- or intermediate-risk outcomes. We identified distinct immunophenotypic features for DUX4-rearranged, PAX5 P80R, ZNF384-R/-like, and Ph-like genotypes. These data in a large adult B-ALL cohort treated with a non–risk-adapted approach on a single trial show the prognostic importance of genomic analyses, which may translate into future therapeutic benefits.

Abstract The dic(9;12)(p12;p11.2) has been described as a rare cytogenetic abnormality in pediatric precursor B-cell ALL. Initial studies suggested that the rearrangement is associated with a favorable outcome, and recent studies demonstrated the presence of a PAX5-ETV6 fusion gene was associated with this cytogenetic abnormality. Twenty cases with a cytogenetic dic(9;12) were identified in the Children’s Oncology Group (COG) cytogenetics databases. FISH analysis with the ETV6-RUNX1 (TEL-AML1) probes was done on 12 of these samples. Five cases were positive for fusion, indicating a cryptic t(12;21)(p13;q22), and also had loss of the ETV6 probe from the chromosome 12 not involved in the t(12;21). Seven cases were negative for fusion and had loss of an ETV6 signal, although one of the latter had a diminished ETV6 signal identified. To determine whether both PAX5-ETV6 and ETV6-RUNX1 rearrangements occurred in some patients, a diagnostic sample from each patient was analyzed by RT-PCR for the PAX5-ETV6 and ETV6-RUNX1 fusion genes. Primers from exon 3 of PAX5 and exon 3 of ETV6 were used for the PAX5-ETV6 analysis and from exon 5 of ETV6 and exon 4 of RUNX1 for the ETV6-RUNX1 analysis. Of the 20 cases, only 8 were RT-PCR positive for the PAX5-ETV6 fusion with the above primers; however, an additional 2 were RT-PCR positive with alternate primers, and all 10 of these were negative for the ETV6-RUNX1 fusion by RT-PCR. Of the remaining 10 patients, 9 were RT-PCR positive for the ETV6-RUNX1 fusion, including all of the ETV6-RUNX1 cases positive by FISH. The gene rearrangement associated with the dic(9;12) in these cases is not known. One patient was negative for both fusions by RT-PCR, negative by FISH for ETV6-RUNX1 rearrangement, yet had loss of an ETV6 signal. No cytogenetic differences could be seen between the 2 groups, either in the appearance of the dic(9;12) or in the other abnormalities identified. These results demonstrate the presence of two mutually exclusive dic(9;12) rearrangements in pediatric ALL; one associated with ETV6-RUNX1 rearrangement and one resulting in PAX5-ETV6 fusion. Both PAX5-ETV6 and ETV6-RUNX1 rearrangements are associated with a favorable prognosis. However, molecular analysis of the dic(9;12) patients must be performed to determine whether the dicentric chromosome results in PAX5-ETV6 fusion or whether the case has ETV6-RUNX1 fusion.

Abstract Early response to therapy, including assessment of MRD is a powerful prognostic factor in childhood ALL. However, there are many other known prognostic factors, and the precise relationship among these and MRD has been incompletely explored. In COG protocol P9900, patients were assigned to one of 3 risk-directed therapies based on NCI risk group, as well as TEL-AML1 translocations (TEL) and simultaneous trisomies of chromosomes 4 and 10 (DT). Infants and Ph+ patients were excluded. Good risk patients (9904) comprised NCI SR patients with either TEL or DT without CNS disease. Poor risk patients (9906) included a subset of NCI HR patients with particularly unfavorable risk factors based largely on age and white count, while 9905 had both NCI SR and HR patients not eligible for 9904 or 9906, including NCI HR patients with TEL or DT. MRD was satisfactorily measured with at least .01% sensitivity by 4-color flow cytometry in the marrow at end of induction (D29) or in blood at Day 8 (D8). D29 MRD was associated with poor outcome in all studies, and in both HR and SR patients on 9905 as shown: Study 4 y EFS ± SE (n) p value MRD <.01% MRD >.01% 9904 Overall 94±1%(668) 75±6%(105) <.0001 TEL-AML1 94±2%(367) 68±12%(38) <.0001 DT 95±1%(316) 80±7%(69) <.0001 9905 NCI-Standard Risk 89±2%(462) 63±6%(119) <.0001 9905 NCI-High Risk 83±4%(292) 49±9%(73) <.0001 9906 74±6%(156) 39±8%(84) <.0001 The proportion of D29 MRD positive DT(17.9%) patients was higher than that of TEL patients (9.4%) but MRD was also prognostic when each group was considered separately; similar findings were seen in HR TEL and DT patients. TEL or DT was associated with a significantly better prognosis in both HR and SR patients who were MRD negative, but were not favorable factors in MRD positive patients. D8 blood MRD was also prognostic in all studies, with higher MRD levels generally associated with poorer outcome. Patients who were both D29 and D8 MRD negative had a good outcome overall (93% 4 y EFS); combining all favorable risk factors, including TEL, DT, NCI risk group, D8 and D29 MRD identified a group of patients (about 13% of B-precursor ALL patients) with 98± 1% 4 y EFS. In multivariate analysis, D29 MRD was the most important prognostic factor. NCI Risk group, DT and D8 blood were also significant, but TEL and day 8 morphologic assessment of marrow were not. We conclude that MRD is a major prognostic factor in childhood ALL even accounting for other risk factors. The prognostic significance of TEL and DT depends on MRD status. The combination of good risk clinical and genetic factors, and absence of MRD in both D8 blood and D29 marrow identifies a group of patients with outstanding outcome on limited therapy.

Abstract Background: Retrospective analyses have demonstrated significantly improved survival for AYA ALL patients (pts) aged 16-21 years (yrs) when treated on pediatric versus adult U.S. NCI Cooperative group regimens where 2-yr event-free survivals (EFS) have been only 35-40%. The purpose of C10403, a large prospective US intergroup trial, was to evaluate the feasibility and effectiveness [with EFS as a primary endpoint), of treating AYA ALL pts (ages 16-39 yrs) using the standard arm of the successful Children's Oncology Group regimen (COG AALL0232) . Methods: Newly diagnosed AYA patients with B-precursor (B-ALL) or T-precursor (T-ALL) ALL were eligible to enroll on C10403. Burkitt type and Ph+ ALL were excluded. The regimen was identical to the Capizzi methotrexate arm of COG AALL0232 (Larsen E. JCO 2011; 29 suppl:3) and consisted of four intensive courses: remission induction, remission consolidation, interim maintenance, delayed intensification, and prolonged maintenance therapy. Pts with M2 marrow response (>5% but < 25% lymphoblasts) after remission induction received an extended remission induction course of therapy. Events were defined as induction failure (M3 [³25% blasts] day 29 of induction or M2 day 43 of extended induction), death, relapse, or second malignancy. Key correlative science studies in a subset of the total accrued population included assessment of Minimal Residual Disease (MRD) using quantitative real-time PCR of clonal IgH or TCR gene rearrangements as well as Low Density Microarray (LDA) assays designed to detect a previously validated gene expression profile (Harvey, R; ASH 2013, abstract 826) which can prospectively identify ALL pts with Ph-like (BCR-ABL1-like) ALL. Results: 318 pts were enrolled on C10403 from 11/2007 to 8/2012; 22 withdrew prior to therapy. Of 296 evaluable pts, the median age at diagnosis was 24 yrs (range: 17 to 39): 25% were 17-20 yrs, 53% were 21-29 yrs, and 22% were 30-39 yrs. The majority had B-ALL (76%) and were male ( 61%). Approximately 25% were non-Caucasian and 15% were Hispanic or Latino. 32% of pts were obese (BMI³30). There were 5 (2%) treatment-related deaths during protocol therapy: liver failure (n=2, both during induction), infection (1 in induction, 1 in consolidation), and ventricular arrhythmia (1 in induction). Overall, treatment toxicities were similar to those reported in the standard arm of COG AALL0232, with an increased thrombosis and early hyperbilirubinemia for C10403 pts, as reported previously (Advani A, ASH 2013, abstract 303). To date, 70 deaths have been reported and 87 pts remain on protocol therapy. With a median follow-up of 28 months for surviving pts, 105 events have been observed. The median EFS overall is 59.4 months (95% CI: 38.4 to NR) and the 2-yr EFS rate overall is 66% (95% CI: 60 – 72%) [Fig 1a] with similar 2-yr EFS rates for B and T- ALL pts (65%, and 68%). The 2-yr OS rate is 78% (95% CI: 72 – 83%)[Fig 1b], which is similar for B (78%, 95% CI: 72 – 84%) and T-ALL, (80%, 95% CI: 70 – 91%). These results allow rejection of the null hypothesis of this Phase II trial that the true median EFS is, at most, 32 months. In multivariable analysis of presenting clinical features, age > 20 years and initial WBC count ³ 30k/microliter were significantly associated with worse EFS and OS. Presence of MRD at day 28 following initiation of induction therapy and presence of a Ph-like gene expression signature were significantly associated with both worse EFS and OS. Notably, absence of detectable MRD noted in 22/58 [38%] evaluable pts at day 28 of induction was associated with 100% EFS (p=0.0006). The Ph-like like signature was detected in 28% of pts tested on C10403 and the 2 yr EFS for these patients was only 52%, compared to 81% for those without Ph-like disease (p = 0.04). Conclusions: This large prospective US adult intergroup trial (C10403) for pts 16-39 years old employing an intensive pediatric regimen demonstrates a significant improvement (compared to historical controls) in AYA EFS and OS and validates this approach for treatment of AYA with ALL by adult hematologists. The improved clinical outcomes and the predictive value of the correlative studies in this trial lay the foundation for the design of future trials, where incorporation of novel agents to eradicate MRD, and/or use of tyrosine kinase inhibitors to target the frequently detected Ph-like ALL in AYA pts may further improve survival for young adults with ALL. Figure 1a Figure 1a. Figure 1b Figure 1b. Disclosures Stock: Sigma-Tau: Membership on an entity's Board of Directors or advisory committees, Research Funding. Advani:Sigma Tau: Membership on an entity's Board of Directors or advisory committees; Jazz: Membership on an entity's Board of Directors or advisory committees. Liedtke:Onyx: Membership on an entity's Board of Directors or advisory committees. Larson:Novartis: Consultancy, Research Funding.