Clearance Of Bone Marrow Blasts Research Articles

Adct-602, a CD22 Targeting Antibody Drug Conjugate Bound to PBD Toxin in Adult Patients with Relapsed or Refractory B-Cell Acute Lymphoblastic Leukemia: A Phase 1 Trial

Introduction: Outcomes of patients (pts) with relapsed or refractory (R/R) B-cell acute lymphoblastic leukemia (B-ALL) remain dismal. CD22 is expressed on lymphoblasts in >90% of pts with B-ALL and is an established therapeutic target. Inotuzumab ozogamicin is an approved CD22 targeting antibody for pts with R/R B-ALL; however, the toxin calicheamicin can lead to veno-occlusive disease (VOD) of the liver, especially after allogeneic SCT (allo-SCT). ADCT-602 is an antibody drug conjugate composed of a humanized monoclonal antibody directed against CD22 and conjugated to SG3199, a pyrrolobenzodiazepine (PBD) dimer cytotoxin. In preclinical studies, ADCT-602 demonstrated potent anti-tumor activity in mouse models of B-cell malignancies. We present here results from an ongoing phase 1/2 trial evaluating ADCT-602 in pts with R/R B-ALL (NCT03698552). Methods: This is an investigator-initiated phase 1/2 trial of ADCT-602 monotherapy in pts with R/R B-ALL. The primary objective of the phase 1 part is to assess the safety and determine the maximum tolerated dose (MTD) and recommended phase 2 dose (RP2D) of ADCT-602. The primary objective of phase 2 is to evaluate efficacy (CR/CRi rate). Eligible pts must be ≥18 years of age with R/R B-ALL with bone marrow blasts ≥5%. CD22 must be expressed in ≥20% blasts. Pts must have adequate organ function (creatinine ≤1.5 mg/dL; ALT and AST ≤2 times upper limit of normal (ULN), ≤5 times ULN if there is liver or bone involvement; total bilirubin ≤1.5 times ULN; LVEF ≥45%). A 3+3 dose-escalation design was used for phase 1. ADCT-602 was initially given IV once every 3 weeks; based on the PK data, the administration schedule was later amended to weekly infusions. Results: From November 2018 to July 2022, 21 pts (11 women, 10 men) with R/R B-ALL were enrolled and received treatment with ADCT-602. The median age was 39 years (range, 21-82) and pts had received a median of 5 (range, 2-9) prior therapies [inotuzumab ozogamicin 12/21 (57%); blinatumomab 18/21 (86%); venetoclax 12/21 (57%)]. A total of 8/21 (38%) had a prior CD19 CAR-T, including 1 pt who had both CD19 and CD22 CAR-T. Ten (10/21, 48%) pts had a prior allo-SCT, including 3 pts with 2 prior allo-SCT. The median pretreatment bone marrow blasts were 70% (range, 16-96). The median CD22 expression on blasts was 97% (range, 33.6-100). A total of 11 pts were treated in the Q3week schedule [30µg/kg, n=3; 60µg/kg, n=4; 90µg/kg, n=4]. As the PK data indicated rapid clearance of the antibody, the trial was amended to allow for weekly dosing. A total of 10 pts were treated at the weekly dose level [30µg/kg, n=3; 40µg/kg, n=4; 50µg/kg, n=3]. One pt (30µg/kg weekly dose level) had grade 4 thrombocytopenia possibly related to ADCT-602. One pt (50µg/kg weekly dose level) had a DLT of prolonged myelosuppression (marrow blast clearance without blood count recovery). No pt had VOD. Notably, all 3 pts treated at the 50µg/kg weekly dose level (a dose level expected to be close to RP2D) had evidence of anti-tumor activity (2 pts achieved MRD negative CR; one pt had bone marrow blast clearance). First pt at this dose level was a 26-yr-old with R/R B-ALL with PAX5-JAK2 fusion with 5 prior therapies including 2 CD19 CAR-T and an allo-SCT who achieved MRD negative CR and is receiving ongoing therapy in Cycle 5. Second pt at this dose level was a 66-yr-old with TP53- and KRAS-mutated B-ALL with 2 prior therapies including modified BFM regimen and blinatumomab who achieved MRD negative CR and is receiving ongoing therapy in Cycle 4. Third pt at this dose level was a 21-yr-old with TP53- and KRAS-mutated B-ALL with 4 prior therapies including inotuzumab and a CD19 CAR-T who had morphologic blast clearance without blood count recovery. Two additional pts treated at lower doses levels (1 each at 30µg/kg Q3week and 30µg/kg weekly schedule) achieved MRD negative CR. All responding pts had CD22 expression noted in >97% of the blasts by flow cytometry. Conclusions: In this phase 1 study in pts with very heavily pretreated R/R B-ALL with a median of 5 prior lines of therapy and high baseline bone marrow tumor burden, single-agent ADCT-602 was well tolerated with one pt with DLT noted at the 50µg/kg weekly dose level. Notably, all 3 pts treated at this dose level had evidence of clinical activity with 2/3 pts achieving MRD negative CR. Due to 1 pt with DLT at this dose level, this cohort is being expanded to treat 3 additional pts. This trial continues to accrue pts and updated data will be presented at the ASH meeting.

Efficacy and safety of venetoclax in combination with azacitidine or decitabine in an outpatient setting in patients with untreated acute myeloid leukemia.

7044 Background: Venetoclax (Ven), a highly selective BCL-2 inhibitor, combined with hypomethylating agents (HMAs) azacitidine (Aza) or decitabine (Dec) is approved for the treatment of newly diagnosed acute myeloid leukemia (ND AML) in patients (pts) who are ineligible to receive intensive chemotherapy. Previous clinical studies initiated Ven + HMA in an inpatient setting due to concerns of tumor lysis syndrome (TLS). This Phase 3b, single-arm, multicenter, open-label study (NCT03941964) evaluated the efficacy and safety of Ven + HMA in a US community-based outpatient setting. Methods: Pts with ND AML who were ineligible to receive intensive chemotherapy, had no evidence of spontaneous TLS at screening, and were deemed an appropriate candidate for outpatient initiation of Ven + HMA by the investigator were eligible. Pts received Ven (400 mg) in combination with Aza (75 mg/m2) or Dec (20 mg/m2) for up to 6 cycles during the study period. Pts could continue receiving commercially acquired Ven after the study period. All pts received TLS prophylaxis. The primary endpoint was the composite complete remission (CR) rate (CR + CR with incomplete hematologic recovery [CRi]) per modified International Working Group criteria. Secondary endpoints included CR or CRi rates and transfusion independence (TI). TLS was assessed per Howard criteria (Howard. N Engl J Med. 2011;364:1844). Results: At the 19 Oct 2021 cutoff date, 60 pts were enrolled and treated (Ven + Aza, n=30; Ven + Dec, n=30). Efficacy outcomes are shown in the Table. The composite CR rate was 58%. CR and CRi rates were 13% and 45%, respectively. Most pts (>50%) maintained TI, and 41% and 57% of pts dependent on red blood cells or platelets, respectively, converted to TI. Bone marrow blast clearance was achieved in 42 pts (70%) at a median 26 days after treatment initiation. The most common (≥50%) AEs were anemia (75%), neutrophil count decrease (55%), white blood cell count decrease (52%), and nausea (50%). Serious AEs occurred in 67% of pts, most commonly (≥15%) febrile neutropenia (28%) and sepsis (15%). Two pts (3%) had TLS; neither event led to treatment discontinuation. Of pts who achieved blast clearance, 12/42 (29%) had a new event of myelosuppression post-blast clearance and prior to the next cycle. Conclusions: The results of this US community-based study indicate that Ven + HMA is an effective treatment option for pts with ND AML and, with appropriate TLS prophylaxis and monitoring, can safely be initiated in an outpatient setting. Clinical trial information: NCT03941964. [Table: see text]

BCL-2 Inhibition in MDS

Enhanced expression of BCL-2 has been associated with more advanced stages of myelodysplastic syndromes (MDS), supporting the clinical rationale to investigate the role of venetoclax in combination with azacitidine (ven-aza) in patients with higher-risk MDS. Similar to the experience in AML, ven-aza produces a rapid and high rate of bone marrow blast clearance, with myelotoxicity as the main adverse effect. In contrast to AML, patients with MDS do not require a venetoclax dose ramp-up, and the starting venetoclax duration is shorter (14 days). In treatment-naïve MDS, ven-aza is associated with an overall response rate (CR/mCR) of 80%, with median overall survival of 28.6 months. A phase 3 trial is in progress.

PRC2 loss of function confers a targetable vulnerability to BET proteins in T-ALL

AbstractT-cell acute lymphoblastic leukemia (T-ALL) is a group of aggressive hematological cancers with dismal outcomes that are in need of new therapeutic options. Polycomb repressor complex 2 (PRC2) loss-of-function alterations were reported in pediatric T-ALL, yet their clinical relevance and functional consequences remain elusive. Here, we extensively analyzed PRC2 alterations in a large series of 218 adult T-ALL patients. We found that PRC2 genetic lesions are frequent events in T-ALL and are not restricted to early thymic precursor ALL. PRC2 loss of function associates with activating mutations of the IL7R/JAK/STAT pathway. PRC2-altered T-ALL patients respond poorly to prednisone and have low bone marrow blast clearance and persistent minimal residual disease. Furthermore, we identified that PRC2 loss of function profoundly reshapes the genetic and epigenetic landscapes, leading to the reactivation of stem cell programs that cooperate with bromodomain and extraterminal (BET) proteins to sustain T-ALL. This study identifies BET proteins as key mediators of the PRC2 loss of function-induced remodeling. Our data have uncovered a targetable vulnerability to BET inhibition that can be exploited to treat PRC2-altered T-ALL patients.

Use of Venetoclax (VEN) and Hypomethylating Agents (HMA) in Newly Diagnosed Acute Myeloid Leukemia (AML) in the United States (US) - Real World (RW) Response, Treatment Duration, Dose and Schedule Modifications

Use of Venetoclax (VEN) and Hypomethylating Agents (HMA) in Newly Diagnosed Acute Myeloid Leukemia (AML) in the United States (US) - Real World (RW) Response, Treatment Duration, Dose and Schedule Modifications

Clinical Benefit of Crenolanib, with or without Salvage Chemotherapy, in Multiply Relapsed, FLT3 Mutant AML Patients after Prior Treatment with Gilteritinib

Clinical Benefit of Crenolanib, with or without Salvage Chemotherapy, in Multiply Relapsed, FLT3 Mutant AML Patients after Prior Treatment with Gilteritinib

Clinical Profile of IMGN632, a Novel CD123-Targeting Antibody-Drug Conjugate (ADC), in Patients with Relapsed/Refractory (R/R) Acute Myeloid Leukemia (AML) or Blastic Plasmacytoid Dendritic Cell Neoplasm (BPDCN)

Clinical Profile of IMGN632, a Novel CD123-Targeting Antibody-Drug Conjugate (ADC), in Patients with Relapsed/Refractory (R/R) Acute Myeloid Leukemia (AML) or Blastic Plasmacytoid Dendritic Cell Neoplasm (BPDCN)

Highlights from Recent Cancer Literature

Highlights from Recent Cancer Literature

TP53 and Decitabine in Acute Myeloid Leukemia and Myelodysplastic Syndromes

BackgroundThe molecular determinants of clinical responses to decitabine therapy in patients with acute myeloid leukemia (AML) or myelodysplastic syndromes (MDS) are unclear.MethodsWe enrolled 84 adult patients with AML or MDS in a single-institution trial of decitabine to identify somatic mutations and their relationships to clinical responses. Decitabine was administered at a dose of 20 mg per square meter of body-surface area per day for 10 consecutive days in monthly cycles. We performed enhanced exome or gene-panel sequencing in 67 of these patients and serial sequencing at multiple time points to evaluate patterns of mutation clearance in 54 patients. An extension cohort included 32 additional patients who received decitabine in different protocols.ResultsOf the 116 patients, 53 (46%) had bone marrow blast clearance (<5% blasts). Response rates were higher among patients with an unfavorable-risk cytogenetic profile than among patients with an intermediate-risk or favorable-risk cytogenetic profile (29 of 43 patients [67%] vs. 24 of 71 patients [34%], P<0.001) and among patients with TP53 mutations than among patients with wild-type TP53 (21 of 21 [100%] vs. 32 of 78 [41%], P<0.001). Previous studies have consistently shown that patients with an unfavorable-risk cytogenetic profile and TP53 mutations who receive conventional chemotherapy have poor outcomes. However, in this study of 10-day courses of decitabine, neither of these risk factors was associated with a lower rate of overall survival than the rate of survival among study patients with intermediate-risk cytogenetic profiles.ConclusionsPatients with AML and MDS who had cytogenetic abnormalities associated with unfavorable risk, TP53 mutations, or both had favorable clinical responses and robust (but incomplete) mutation clearance after receiving serial 10-day courses of decitabine. Although these responses were not durable, they resulted in rates of overall survival that were similar to those among patients with AML who had an intermediate-risk cytogenetic profile and who also received serial 10-day courses of decitabine. (Funded by the National Cancer Institute and others; ClinicalTrials.gov number, NCT01687400.)

Abstract NG02: Polyclonal and heterogeneous resistance to targeted therapy in leukemia

Abstract NG02: Polyclonal and heterogeneous resistance to targeted therapy in leukemia

The Safety and Activity of BMS-906024, a Gamma Secretase Inhibitor (GSI) with Anti-Notch Activity, in Patients with Relapsed T-Cell Acute Lymphoblastic Leukemia (T-ALL): Initial Results of a Phase 1 Trial

Background: Activating mutations in Notch receptors are found in multiple hematopoietic malignancies, including > 50% of patients with T-ALL, making it the most common genetic abnormality in this disease. GSIs block activation of Notch receptors and limit growth and survival in pre-clinical T-ALL models. However, various GSIs evaluated in clinical trials have had on target toxicities and have not been reported to show significant responses. CA216002 is a multicenter phase 1 trial designed to assess the safety of a novel intravenous GSI BMS-906024 in patients with relapsed or refractory T-ALL and T-cell lymphoblastic lymphoma (T-LL). We are presenting the initial toxicity profile and response data on this trial.Methods: Adults with relapsed/refractory T-ALL or T-LL were enrolled and received BMS-906024 intravenously weekly at doses of 0.6 mg, 4 mg, and 6 mg. Due to the rapid progression of T-ALL in many cases, administration of glucocorticoids or other agents was permitted and dosing guidelines for dexamethasone were provided in the protocol.Results: As of July 2, 2014, safety and response data are available on 25 patients (age 18-74 yrs) with relapsed/refractory T-ALL/T-LL that received at least one dose of BMS-906024, at doses of 0.6 mg (n=1), 4 mg (n=10), and 6 mg (n=14). Seven patients did not complete the first 4-week cycle due to rapid disease progression or disease-related death (n=5), infusion reaction (n=1), or an unrelated adverse event (n=1).Safety: The drug-related grade 3-5 adverse events included grade 4 events of anemia, hypophosphatemia, and thrombocytopenia, and grade 3 events of diarrhea, febrile bone marrow aplasia, hepatotoxicity, hypophosphatemia, pancytopenia, and tumor lysis syndrome (n=1 each). Drug-related diarrhea was common (n=11, 44%), consistent with expectations for Notch inhibition, but was generally grade 1-2 with only one grade 3 event. One dose-limiting toxicity involving grade 3 elevations of ALT and AST without bilirubin elevation (reported as grade 3 hepatotoxicity) occurred at the 4 mg dose level. One death not related to disease progression occurred, due to GI and post-surgical hemorrhage associated with pancytopenia; hemorrhage was considered not related, but pancytopenia was considered related to study drug.Responses: Eight patients (32%; 4 at 4 mg and 4 at 6 mg) had at least 50% reduction in bone marrow (BM) blasts, including one formal CR and one PR (both at 6 mg), and three of these eight had 98-100% clearance of BM blasts. (One patient, marked “*” below, began the study with 0.1% BM blasts and is not included in the eight.) The patient who achieved a CR began the study with 85% BM blasts and an absolute peripheral blood (PB) blast count of 38 k/mcL. By the end of the first cycle the BM and PB were cleared of blasts, and by the end of the second cycle there was count recovery. This patient received dexamethasone during the first cycle only, and left the study after 3 cycles in CR for an allogeneic transplant. The patient who achieved a PR began with 32% BM blasts, and by the end of the first cycle the BM blasts had decreased to 7% with improvement in ANC. The additional six patients with 50-100% decreases in BM blasts had residual lymphadenopathy, had incomplete count recovery or failed to meet other criteria which prevented them from being considered CR or PR based on the protocol definitions. One of these six patients also received hydroxyurea beginning on study day 16.Biomarkers: The figure shows change in BM blasts in 12 patients with paired BM assessments and Notch mutation status available. BM responses occurred in both Notch mutant and wildtype patients.Conclusions: Overall 8 of the 25 patients (32%) showed at least 50% reduction in BM blasts including one CR and one PR. Although the contribution of concurrent glucocorticoid therapy to the improvement in some patients is not clearly defined, the multiple responses on this trial suggest anti-leukemia activity of BMS-906024. This represents the first Notch targeting trial leading to multiple responses in relapsed/refractory T-ALL. BMS-906024 was relatively well tolerated, with minimal diarrhea in this population. The weekly dosing of this long-acting GSI shows promise for targeting Notch in T-ALL. Pharmacokinetic and additional biomarker data will be presented. [Display omitted] DisclosuresZweidler-McKay:BMS: Research Funding. Off Label Use: BMS-906024 is in early Phase I clinical trials, and does not yet have an FDA-approved indication.. Douer:BMS: Research Funding. Ottmann:BMS: Consultancy, Honoraria, Research Funding. Vey:BMS: Honoraria. Thomas:BMS: Research Funding. Zhu:BMS: Employment. Huang:BMS: Employment, Equity Ownership. Bajaj:BMS: Employment. Fischer:BMS: Employment, Equity Ownership.

Membrane Tyrosine Kinase Receptors Kit and FLT3 are an Important Targets for the Therapy of Acute Myeloid Leukemia

KIT and FLT3 are class III trans membrane tyrosine kinases playing key roles in the control of hematopoietic stem cell survival and proliferation. KIT is mutated in about 2.5-3% of acute myeloid leukemia (AML) patients mainly by point mutations occurring at the level of tyrosine kinase domains. FLT3 is mutated in about 30% of AML patients, either by internal tandem duplication of the juxtamembrane domain or by point mutations occurring at the level of tyrosine kinase domains. All these types of mutations lead to the constitutive activation of KIT and FLT3 receptors, respectively. In some AML subsets, the occurrence of FLT3/ITD mutation is associated with a poor prognosis. These observations have represented the basis for the development of a large number of Tyrosine Kinase Inhibitors (TKIs) with activity against KIT and FLT3. Some of these inhibitors are still in the preclinical phase, but many have been tested in phase I/II/III clinical studies. Although these inhibitors when used as single agents have lead to a significant reduction of the number of leukemic blasts, they have produced only transient and limited clinical responses. This efficacy may be related to the limited inhibitory caefficacy of these inhibitors, occurrence of resistance and to the complexity of the genetic abnormalities occurring in AMLs. However, recently Quizartinib, a potent FLT3 inhibitor, showed an impressive rate of remission induction in patients with chemotherapy-refractory FLT3-ITD-positive AMLs, but most remissions do not meet classical criteria of complete remissions and instead represent clearance of bone marrow blasts with incomplete recovery of blood cell counts. However, the majority of these patients after an initial sustained response exhibit a leukemic relapse due to the rare pre-exisisting or new FLT3-ITD-TKD mutants surviving to the treatment with this drug and becaming driver leukemic clones. The combination of various types of FLT3 TKIs, including a type II TKI like Quizartinib with a type I FLT3 inhibitor efficiently targeting TKD mutants, such as Crenolanib, or the combination of FLT3 inhibitors with other molecularly targeted agents inhibiting other pathways activated in leukemic cells would determine a major progress in leukemia therapy. The efficacy of FLT3 TKIs in combination with standard anti-leukemic chemotherapeutics is also under evaluation in several combination clinical trials. It is expected that these trials could determine an improvement in the negative prognosis of AML patients with FLT3/ITD mutations. Keywords: Membrane tyrosine kinase receptors, leukemia, cytogenetic.

Poor Prognosis With Different Induction Rate Was Observed In Children With Acute Myeloid Leukemia and FLT3-ITD According To The ITD/WT Allelic Ratio: A Result From The Japanese Pediatric Leukemia/Lymphoma Study Group

BackgroundAcute myeloid leukemia harboring internal tandem duplication of fms-like tyrosine kinase 3 (AMLFLT3-ITD) is associated with poor prognosis, but the previous studies have reported that the inferior outcome is only confined to those with high allelic ratio (AR) of ITD/wild type (WT). In our previous AML99 study (2000-2002), AMLFLT3-ITD showed a poor outcome compared to the WT cases (5-year OS; 35% vs. 84%, P<0.0001). We, therefore, assigned all the patients with AMLFLT3-ITD to receive hematopoietic stem cell transplantation (HSCT) in first remission (1CR) in the JPLSG AML-05 study. Patients & MethodsAML-05 study, registered at http://www.umin.ac.jp/ctr/ as UMIN000000511, is a Japanese nation-wide multi-institutional study for children (age<18 years) with de novo AML and enrolled 443 eligible patients from Nov. 2006 to Dec. 2010. Cases with acute promyelocytic leukemia or Down syndrome were excluded. FLT3-ITD was examined centrally for all the patients. After the 2 consecutive induction chemotherapies [(ECM: etoposide, Ara-C, and mitoxantrone) and (HCEI: HD Ara-C, etoposide, and idarubicin)], all the AMLFLT3-ITD patients were allocated to the high risk group and further received intensification therapy including HD Ara-C followed by HSCT in 1CR. All DNA samples were extracted from the first diagnostic bone marrow or peripheral blood and subjected to PCR and direct sequencing. AR of FLT3-ITD/WT was examined by GeneScan, and defined AR >0.4 as high and AR ≤ 0.4 as low as previously reported (Meshinchi S. Blood2006). ResultsWe found 47 patients (10.6%) with AMLFLT3-ITD in this study (30 males, 17 females, and median age of 11 years at diagnosis). The median WBC count was 65,300/ml (3,690 - 522,050/mL). FAB classification included M1 (n=10), M2 (n=9), M4 (n=9), and M5 (n=11), and AML with normal karyotype was dominant (19/47, 40.4%).Of the 29 patients (61.7%) who achieved CR, twenty-seven received HSCT in 1CR and 19 patients survived (19/27, 70.4%). On the other hand, 14/16 non-CR patients received HSCT, but only 4 survived. The only demographic difference between the 29 CR and 16 non-CR cases was the median WBC count at diagnosis (19,000 vs. 124,000/μL, P<0.001), and rapid clearance of bone marrow blasts after single induction course was observed in the CR group (median blast percentage dropped from 73% to 1.1% in the CR group, while that was 85% to 30.6% in the non-CR group). Finally, five-year OS, DFS and EFS for all 47 AMLFLT3-ITD patients were 41.3%, 58.4% and 36.1%, respectively.AR was analyzed in 44 patients with median ratio of 0.68 (range, 0.11 to 4.47). Median AR was not different between CR vs. non-CR cases (0.53 vs. 0.72). There were no difference in 5-year OS (52.8% vs. 42.5%, P=0.302), DFS (54.5% vs. 64.5%, P=0.524), and EFS (50.0% vs. 34.4%, P=0.283) between patients with low (n=12) and high AR (n=32), however, induction rate was significantly higher in the low AR patients (91.7% vs. 53.1%, P=0.018).It was rather surprising that all FLT3-ITDs were found only in JM domain and not in TKI domain in the current trial. In addition, six of 47 (12.8%) AMLFLT3-ITD patients had NPM1mutation simultaneously, and all received HSCT at 1CR and survived. Discussion and ConclusionWe observed a different induction rate between AMLFLT3-ITD patients with low and high AR, but poor final outcomes in both. Regardless of the level of AR, patients with AMLFLT3-ITD, especially who fail to achieve remission, have dismal outcome and effective therapy combined with novel FLT3 inhibitor is urgently needed to overcome the disease. Disclosures:No relevant conflicts of interest to declare.

Allogeneic Hematopoietic Stem Cell Transplantation (HSCT) In Adults With Philadelphia Chromosome (Ph)-Negative Acute Lymphoblastic Leukemia (ALL): Results From The Group For Research On Adult ALL (GRAALL)

▪ PurposeThe pediatric-inspired intensified GRAALL protocol yielded a marked improvement in the outcome of adults with Ph-negative acute lymphoblastic leukemia (ALL) (Huguet et al,JCO 2009), raising the issue of the place of allogeneic HSCT in this new context. We report here the results associated with HSCT in first complete remission (CR) in younger adults treated in the GRAALL-2003/2005 trials. Patients and methodsIn these trials, HSCT was offered in first CR to patients aged 15-55 years with ALL at higher risk of relapse. High-risk factors included white blood count >30 x 109/L for B-lineage ALL, central nervous system (CNS) involvement, t(4;11)/MLL anomalies, t(1;19), low hypodiploidy/near triploidy, complex karyotype, early resistance to the steroid prephase (CsR), early resistance to chemotherapy (ChR) as assessed by poor bone marrow blast clearance at day 8, and late CR. Per protocol, HSC donor should be a matched sibling or an unrelated donor (10/10 or eventually 9/10 HLA matched) and conditioning regimen should include single fraction 10-Gy or fractionated 12-Gy total body irradiation (TBI) and high-dose cyclophosphamide. The role of HSCT was evaluated by HSCT versus no-HSCT cohort comparison (Mantel-Byar time-dependent analysis). ResultsAmong the 522 high-risk patients eligible, 283 (54%) actually received HSCT in first CR (185 B-lineage and 98 T-lineage ALL; median age, 31 years). There were no significant differences in baseline characteristics and early response between HSCT and no-HSCT cohorts, except more HSCT patients with t(4;11)/MLL anomalies. Among the 283 HSCT patients, 46 had t(4;11)/MLL anomalies, 13 had CNS disease, 116 had CsR and 176 had ChR ALL. Origin of HSC was 140 sibling and 143 unrelated donors, including 47 unrelated donors with 1 HLA mismatch. The following HSCT protocol violations were observed: a) conditioning did not include TBI in 17 patients; b) 10 patients received reduced-intensity conditioning (RIC); and c) 13 patients received cord blood HSCT. These patients remained in the HSCT cohort for the analysis. With a median post-transplant follow-up of 3.5 years, post-HSCT cumulative incidence of relapse (CIR), non-relapse mortality (NRM) and relapse-free survival (RFS) were estimated respectively at 19% (95% CI, 15-25), 16% (95% CI, 12-21) and 64% (95% CI, 58-70) at 3 years, without any RFS difference between sibling and unrelated donors. A marked trend for a higher NRM was observed in patients aged 45 years or more (26% versus 13% at 3 years; HR, 1.6; p=0.059), while post-transplant CIR was similar in older and younger patients. Mantel-Byar RFS estimations showed no significant difference between both HSCT and no-HSCT cohorts (HR, 0.80; p=0.13), meaning that the risk factors used in these protocols failed to identify patients who could significantly benefit from HSCT in first CR. As minimal residual disease (MRD) had a major prognostic impact, we retrospectively analyzed the effect of HSCT in the 278/522 patients evaluated for 6-week Ig/TCR MRD level (154 HSCT and 124 no-HSCT patients, including 92 and 62 patients with MRD >=10-4, respectively). Mantel-Byar RFS estimations showed that HSCT did not benefit to patients with MRD <10-4 (HR, 1.2; p=0.67) as opposed to those with MRD >=10-4 (HR, 0.6; p=0.02), with a positive HSCT-by-MRD interaction (p=0.04) (Figure 1). [Display omitted] ConclusionIn adult patients with high-risk ALL in first CR treated in the GRAALL-2003/2005 trials, myeloablative allogeneic HSCT from sibling and unrelated donors was associated with a 64% RFS at 3 years. The 26% NRM observed at 3 years in patients aged 45 years or more suggests considering RIC-HSCT in these patients. MRD response appears to be a powerful tool to select patients who might benefit from HSCT. This selection tool will be prospectively evaluated in the next GRAALL-2013 trial.ND and AH contributed equally to the work. Disclosures:No relevant conflicts of interest to declare.

Pretreatment long interspersed element (LINE)-1 methylation levels, not early hypomethylation under treatment, predict hematological response to azacitidine in elderly patients with acute myeloid leukemia

BackgroundEpigenetic modulations, including changes in DNA cytosine methylation, are implicated in the pathogenesis and progression of acute myeloid leukemia (AML). Azacitidine is a hypomethylating agent that is incorporated into RNA as well as DNA. Thus, there is a rationale to its use in patients with AML. We determined whether baseline and/or early changes in the methylation of long interspersed element (LINE)-1 or CDH13 correlate with bone marrow blast clearance, hematological response, or survival in patients with AML treated with azacitidine.MethodsAn open label, phase I/II trial was performed in 40 AML patients (median bone marrow blast count was 42%) unfit for intensive chemotherapy treated with azacitidine 75 mg/m2/day subcutaneously for 5 days every 4 weeks. Bone marrow mononuclear cell samples were taken on day 0 (pretreatment) and day 15 during the first treatment cycle; LINE-1 and CDH13 methylation levels were quantified by methylation-specific, semiquantitative, real-time polymerase chain reaction.ResultsTreatment with azacitidine significantly reduced LINE-1 but not CDH13 methylation levels over the first cycle (P < 0.0001). Absolute LINE-1 methylation levels tended to be lower on day 0 (P = 0.06) and day 15 of cycle 1 (P = 0.03) in patients who went on to achieve subsequent complete remission, partial remission or hematological improvement versus patients with stable disease. However, the decrease in LINE-1 methylation over the first treatment cycle did not correlate with subsequent response (P = 0.31). Baseline methylation levels of LINE-1 or CDH13 did not correlate with disease-related prognostic factors, including cytogenetic risk, relapsed/refractory AML, or presence of NPM1 or FLT3 mutations. No correlation was observed between LINE-1 or CDH13 methylation levels and overall survival.ConclusionAnalysis of baseline LINE-1 methylation levels may help identify elderly AML patients who are most likely to respond to azacitidine therapy.

Targeting Hypoxia and AKR1C3 with PR104 in Patients with Acute Leukemia

Abstract 3615We have recently demonstrated vast expansion of hypoxic areas in the leukemic microenvironment (Benito et al, PLoS One,2011; 6: e23108). These findings provided rationale for utilization of hypoxia activated pro-drugs (HAP). The pre-prodrug PR104 is rapidly converted systemically to its alcohol metabolite PR104A, which then undergoes metabolic activation to DNA-crosslinking nitrogen mustards catalyzed by hypoxia-dependent reductases, and by aldo-keto reductase 1C3 (AKR1C3), independently of hypoxia. Impressive activity in murine leukemia models, high AKR1C3 expression in AML blast cells (Birtwistle et al., Mutat Res 2009; 662: 67) and the observation of dose-limiting myelosuppression in solid tumor phase 1 studies (Jameson et al., Cancer Chem Pharmacol 2010;65:791) served as rationale for a Phase I/II Study of PR104 in patients (pts) with relapsed/refractory acute leukemia. To evaluate the extent of bone marrow (BM) and peripheral blood (PB) hypoxia at different time points, the hypoxia marker Pimonidazole (PIM) was administered intravenously in consenting patients. Further, AKR1C3 activity was monitored in acute leukemia blasts. Methods:Pts with relapsed/refractory AML or ALL ≥1 prior treatment received PR104 with response and toxicity assessed by day 42. Hypoxia tracer PIM was infused over 20 min at 0.5 g/m2 prior to a BM biopsy and collection of PB at baseline, day 14 (D14) or D28 relative to PR104 administration. Degree of hypoxia was determined by FACS 16 (+/− 6) hrs after PIM administration. The activity of AKR1C3 was measured with a coumberone fluorogenic assay, using SN34037 as a selective AKR1C3 inhibitor, in BM biopsies or PB prior to PR104 administration and was compared to BM or PB samples from normal donors. Results:The clinical outcomes of the entire study will be reported separately. At MD Anderson Cancer Center, 39 pts have received PR104 at doses of 1.1 (3pts), 1.6 (1pt), 2.2 (1pt), 3 (17pts) or 4 gm/m2 (17pts) as 1-hr intravenous infusion q 2 wks for up to 3 cycles. Nineteen (49%) had ≥2 prior treatments and 34 (87%) had a first CR duration of <52 wks. Five pts (13%) had reduction of BM blasts by > 50 percent from baseline on D14. Additionally, 9 pts (23%) had BM aspirates on D14 that yielded insufficient samples and therefore the % of blasts could not be assessed. Four of 34 patients (12%, 95% CI) at 3 or 4g/m2 had responses and proceeded with stem cell transplant. No responses were seen in the 5 patients given PR104 at doses < 3gm/m2.The extent of hypoxia was evaluated by PIM in BM on Day 14 after PR104 in 12 pts using FACS : in 3 pts with clearance of BM blasts, the % PIM+ cells ranged from 0.2% to 9.7%, while in 9 pts with persistent disease, hypoxic cells represented 7.3%-99% of the BM cells. In 3 pts, all with persistent disease, PIM was also administered prior to PR104, and PIM baseline positivity was compared to PIM on D14 or D28 post PR104. In 2 cases the % of PIM+ cells went up from 10% to 20% (% BM blasts: baseline=15; D14=hypocellular) or from 0.6% to 4% (% BM blasts: baseline=75;D18=28) respectively while in the other there was no significant change between the two time points and the %PIM+ cells remained at 7% (% BM blasts: baseline=48%; C1D14=72%). Low level hypoxia in these 3 pts was associated with lack of response to PR104. When possible, PIM staining was compared in BM vs PB samples (N=13). Hypoxic cells were readily detectable in PB consistent with preclinical data by Azab et al. (Blood, 2012, 119:5782), although the % of PIM+ cells was lower than in BM (Average %PIM+ cells: BM 14.4+/−4.5; PB 9+/−3.7), suggesting that these circulating “hypoxic” cells have been labeled by PIM in the BM and subsequently egressed into PB. The activity of AKR1C3 reductase was higher in AML (N=4) or ALL samples (N=6) than in normal PB or BM (N=4) (average AML=2.08+/−0.52; ALL=1.22+/−0.46; NBM=0.77+/−0.007; NPB=0.27+/−0.008). There was no correlation between pre-treatment AKR1C3 activity and achievement of CR. Conclusions:This is the first study measuring hypoxia in patients with leukemia using PIM hypoxia tracer. PIM expression after PR104 administration indicates that hypoxia is a prevalent feature of the leukemic microenvironment and associates with disease burden. AKR1C3 appears to be upregulated in acute leukemias and its potential as a biomarker and/or as a target should be explored. Targeting hypoxia and AKR1C3 with PR104 is feasible and warrants further evaluation in acute leukemias. Disclosures:Wilson:Proacta, Inc.: Employment, Stock Other. Melink:Proacta, Inc.: Employment, Stock Other. Estey:Proacta, Inc.: Research Funding. Gutheil:Proacta, Inc.: Employment, Stock Other. Konopleva:Proacta, Inc.: Research Funding.

Analysis of in Vitro Activity of the Clinically-Active ABL/FLT3 Inhibitor Ponatinib (AP24534) Against AC220-Resistant FLT3-ITD Mutants

Abstract 930 Background:Activating mutations in FLT3 are detected in approximately 30 percent of adult acute myeloid leukemia (AML) cases, most commonly in-tandem duplication (ITD) events. Ponatinib (AP24534) is a potent inhibitor of ABL and FLT3 that has shown clinical activity in CML as well as in a limited experience with FLT3-ITD-positive acute myeloid leukemia (AML) with 2/7 kinase inhibitor-naïve AML patients achieving CRi in a phase I study (Talpaz et al, ASCO 2011, abstract #6518). We recently reported that the FLT3 inhibitor AC220, which has achieved an interim composite CR rate of 43% in a phase II study in relapsed/refractory AML (Cortes, et al, EHA 2011, abstract #1019) is vulnerable to a limited number of resistance-conferring kinase domain mutations in vitro (Smith et al, AACR 2011, abstract #4737). Mutations at 2 of these residues, F691 and D835, have been identified in 9/9 FLT3-ITD+ patients who relapsed after achieving clearance of bone marrow blasts on AC220 (Smith et al, ASH 2011, submitted). Notably, AC220-resistant mutations were found to confer cross-resistance to sorafenib. Given that ponatinib retains activity against a wide range of TKI-resistant BCR-ABL mutants, we sought to test its activity against AC220-resistant mutants. Results:We assessed the activity of ponatinib against highly AC220-resistant FLT3-ITD mutations F691I/L, D835V/Y and Y842C/H. Ponatinib potently suppressed the growth of Ba/F3 cells transformed with native FLT3-ITD with an inhibitory concentration 50 (IC50) of 2 nM. Ba/F3 cells transformed with the “gatekeeper” F691I mutation retained sensitivity to ponatinib at a similar concentration (5 nM). This substitution is analogous to the BCR-ABL T315I mutation, which is clinically sensitive to ponatinib. The remaining AC220-resistant FLT3-ITD mutants, including the gatekeeper F691L substitution, conferred a substantial degree of relative cross-resistance to ponatinib. Mutations at the activation loop residue D835 confer the highest degree of resistance. In an effort to identify other substitutions in FLT3-ITD that are capable of conferring ponatinib resistance in vitro, we employed an in vitro mutagenesis strategy (Azam et al, Cell, 2003) of FLT3-ITD in varying concentrations of ponatinib. In a preliminary analysis, we have identified resistance-causing substitutions at D835, as well as other residues in the FLT3 activation loop including D839 and N841. Interestingly, one of these substitutions, D835N, confers resistance to ponatinib but not to AC220.A molecular analysis of the ponatinib/FLT3 complex based on the crystal structure of ABL/ponatinib was performed and revealed that isoleucine substitution at the FLT3 “gatekeeper” residue (F691I), as with the T315I mutation in Abl, does not creates substantial steric clash with ponatinib. In contrast, the leucine substitution, (F691L), is more bulky than isoleucine and may cause more steric hindrance. In addition, as leucine is more rigid than isoleucine, more energy would be required for the F691L mutation to adopt a conformation compatible with ponatinib binding. As ponatinib binds to the “DFG-out” inactive conformation of FLT3, activation loop mutations such as D835V/Y and Y842C/H likely destabilize the activation loop conformation of FLT3 required for ponatinib binding. Conclusions:Our studies demonstrate that gatekeeper and, in particular, activation loop substitutions in FLT3-ITD, confer a high degree of cross-resistance to the clinically-active FLT3 TKIs described to date. Ponatinib retains in vitro activity against the gatekeeper mutation FLT3-ITD/F691I, which confers a high degree of in vitro resistance to AC220, but leucine substitution at this residue notably confers a higher degree of resistance to ponatinib. Activation loop mutations confer substantial degrees of in vitro cross-resistance to ponatinib and are predicted to confer clinical resistance. Select substitutions at D835 appear to confer selective resistance to ponatinib. Categorization of the spectrum of resistance-conferring mutations may facilitate a more personalized approach toward patients with FLT3-ITD+ AML treated with clinically-active TKI therapy. Disclosures:Off Label Use: Investigational agent ponatinib will be discussed. Zhu:Ariad Pharmaceuticals: Employment. Shah:Ariad: Consultancy, Research Funding; Novartis: Consultancy; Bristol-Myers Squibb: Consultancy, Research Funding.

Genetic and Epigenetic Defects in DNA Repair Lead to Synthetic Lethality of Poly (ADP-Ribose) Polymerase (PARP) Inhibitors in Aggressive Myeloproliferative Disorders

Abstract 400▪FN2▪This icon denotes a clinically relevant abstractPatients with primary and secondary myelofibrosis (MF) have a worse prognosis than those with essential thrombocytosis (ET) or polycythemia vera (PV). MF and chronic myelomonocytic leukemia (CMML) share chromosomal and genetic lesions such as ASXL1 and JAK2 mutations, but effective treatments are lacking. The aim of the study was to identify perturbed pathways in MPN and CMML that were amenable to targeted molecular therapies. In a large genomic analysis of MPN cases, we identified recurrent deletions of multiple DNA repair genes, including BRCA2 and Fanconi anemia (FANC) proteins, which have been associated with poly (ADP-ribose) polymerase (PARP) inhibitor sensitivity. Neoplastic cells from these patients are hypersensitive to PARP inhibitors in vitro and may provide a therapeutic strategy to improve treatment response for patients with advanced MPNs.Genomic screens utilizing SNP-A karyotyping were performed on primary cells from 144 patients with either ET, PV, or MF (90 were previously reported, McDevitt et al., ASH 2009). We focused on the potential functional relevance of recurrent genomic deletions, including BRCA2, by performing a GO analysis using the EASE software application (Hosack et al. 2003). This revealed statistically significant (p≤0.05) enrichment of 13 biological pathways. Notably, genes involved in cell cycle regulation and DNA repair (DR) were enriched in MF loss regions (p=0.007) as compared to regions lost in ET and PV. Several genes directly involved in DR including BRCA2, XRCC2, and several members of the FANC pathway, also critical for DNA crosslink repair, were deleted or present in copy neutral LOH regions. DNA methyltransferase inhibitors are being tested clinically in MF patients, and both cell cycle and DNA repair genes have been identified as epigenetically silenced in hematological malignancies. We therefore screened for BRCA1, BRCA2, FANC-C, L, and N promoter CpG island methylation in a series of 48 MPN samples. No methylation was identified in BRCA2 and FANC members, suggesting a potential haploinsufficiency mechanism. Methylation of BRCA1 was identified in a small number of cases and is under further study in a larger cohort to investigate the effects on BRCA1 expression, DR and sensitivity to PARP inhibitors.Based on these genetic and epigenetic findings, we then focused on a functional analysis of the homologous recombination (HR) pathway. Leukocytes from normal controls and MPN patients were exposed to ionizing radiation (IR) and stained for Rad51 foci, a marker of HR activity. Six of 15 MPN/CMML samples (40%), but none of the controls failed to form IR-induced Rad51 foci, suggesting impaired HR. Of the samples that demonstrated defects in HR [MPN-U, MF, CMML (2), MDS/MPN-U, and CML], there was no significant correlation between the MPN subtype, the JAK2 mutation status, or the specific metaphase karyotype, but the most sensitive case in our series exhibited a deletion of Ch13q that spanned the BRCA2 gene.We then examined sensitivity of MPN vs. normal myeloid progenitors to the PARP inhibitors veliparib and/or olaparib in methylcellulose (MC)-based colony forming assays. Failure to form Rad51 foci with irradiation was statistically correlated with PARP inhibitor sensitivity (p = 0.021). When an expanded series of cases were then analyzed for PARP inhibitor sensitivity using the MC colony assay, lower IC50s for both veliparib and olaparib were observed in MPN cases (N= 25, IC50S=2.69uM vs. 11.2uM, N=15 IC50S=.64uM vs. 1.27uM, respectively) relative to normal controls (p =.0003, p =.05, via Wilconon rank-sum test respectively).Two cases in this series were treated on a clinical trial combining the ABT-888 PARP inhibitor with salvage chemotherapy consisting of carboplatin and topotecan (Karp et al., ASH 2010). Both patients, one with sAML evolving out of PPV-MF, and a second with accelerating MPN-U, had failed four prior therapies but achieved complete clearance of bone marrow blasts at day 14. Interestingly, cells from this MPN-U patient (13q-) were the most sensitive to PARP inhibition in vitro. Additional accrual and correlative evaluations are underway and will be updated at the meeting. Collectively, these results demonstrate that a subset of MPN and CMML patients have intrinsic genetic and epigenetic defects affecting the FANC and HR pathways, providing pre-clinical rationale for the use of PARP inhibitors in the treatment of aggressive MPN and CMML. Disclosures:No relevant conflicts of interest to declare.

Validation of FLT3-ITD As a Therapeutic Target in Human Acute Myeloid Leukemia

Abstract 937 Background. Activating in-tandem duplication (ITD) mutations within the FLT3 juxtamembrane region are detected in ∼25% of adult acute myeloid leukemia (AML) cases and portend a poor prognosis. AC220 (quizartinib) is a potent selective investigational FLT3/KIT inhibitor with encouraging preliminary clinical activity, as evidenced by a composite complete remission rate of 43% in 53 chemotherapy refractory/relapsed AML patients evaluable for an interim analysis of the ongoing phase II study in FLT3-ITD+ relapsed/refractory AML (Cortes et al, EHA 2011 abstract 1019). Many patients who initially respond ultimately suffer disease progression. We sought to utilize the clinical efficacy of AC220 to determine if FLT3-ITD is a valid therapeutic target in human AML. A saturation mutagenesis strategy identified amino acid substitutions at three amino acid residues (F691, D835, Y842) in FLT3-ITD that confer a high degree of resistance to AC220 in vitro. Of these, substitutions at F691 and D835 conferred the greatest degree of relative resistance. Results. To assess the validity of FLT3-ITD as a therapeutic target in AML, we analyzed paired pretreatment and relapse samples obtained from a cohort of 9 FLT3-ITD-positive AML patients enrolled in the exploratory part of the ongoing phase II study of AC220 in relapsed/refractory AML (clinicaltrials.gov NCT00989261) who relapsed after initially achieving morphologic clearance of bone marrow blasts to <5% on treatment. Through RT-PCR subcloning and sequencing of the FLT3 kinase domain, we observed evolution of one or more acquired kinase domain mutations on the FLT3-ITD containing allele in all 9 cases at relapse. Clinically detected mutations were restricted to the “gatekeeper” residue F691 and/or the activation loop residue D835 (F691L, n=3, D835Y, n=4; D835V, n=2, D835F, n=1). Each of these mutations successfully transformed Ba/F3 cells to IL-3 independence and conferred substantial resistance to AC220 in cell growth and cell-based biochemical assays. All of the AC220-resistant mutations conferred substantial in vitro cross-resistance to sorafenib, which has been reported to harbor clinical activity in a small number of FLT3-ITD-associated AML cases.In an expanded analysis of genomic DNA samples from 30 patients enrolled in the exploratory part of the Phase II study who discontinued study drug for any reason, we observed the occurrence of acquired mutations in the kinase domain (D835 and F691) in a total of 10 of 30 (33%) patients at the off study timepoint. One patient had a D835Y mutation prior to going on AC220.Molecular docking studies were undertaken to provide mechanistic insights into the structural basis of resistance conferred by AC220-resistant mutations. These studies revealed that AC220 likely binds strongly to the DFG-out inactive FLT3 kinase domain. AC220 directly interacts with the gatekeeper residue F691, explaining the drug-resistance associated with the F691L mutation. Mutations at D835 and Y842 may potentially de-stabilize the inactive conformation, and result in a more active, AC220 binding-deficient FLT3 kinase. Indeed, substitutions at these residues are known to activate FLT3 in the absence of an ITD mutation.To more precisely assess the frequency and identity of resistance-conferring mutations at relapse, we analyzed a subset of samples using single molecule real-time (SMRT™; Pacific Biosciences, Menlo Park, CA) sequencing, which can generate reads of sufficient length to enable focused interrogation of the kinase domain of FLT3-ITD alleles. With this assay, more than 350 reads of >1000 nucleotides were reliably obtained. Analyses of pretreatment and relapse samples from four patients confirmed the presence of resistance-conferring FLT3-ITD kinase domain mutations at F691 or D835 at relapse in 36–60% of FLT3-ITD sequence reads. Additionally, this method detected polyclonal resistance in two of the four samples assessed. Conclusions. Our studies validate FLT3-ITD as a therapeutic target in a proportion of AML cases, and demonstrate that the clinical activity of AC220 is mediated by FLT3-ITD inhibition. AC220-resistant FLT3-ITD gatekeeper and activation loop mutations identified in clinical samples from relapsing patients represent high-value therapeutic targets for next-generation FLT3 inhibitors. Disclosures:Off Label Use: AC220 is an investigational agent and has no approved drug indication in AML. Chin:Pacific Biosciences: Employment. Hunt:Ambit Biosciences: Employment. Levis:Ambit Biosciences, Inc: Consultancy. Travers:Pacific Biosciences: Employment. Wang:Pacific Biosciences: Employment. Kasarskis:Pacific Biosciences: Employment, Equity Ownership. Schadt:Pacific Biosciences: Employment, Equity Ownership.

Treatment of High-Risk (HR) Philadelphia Chromosome-Negative (Ph-) Adult Acute Lymphoblastic Leukemia (ALL) According to Baseline Risk Factors and Minimal Residual Disease (MRD). Results of the PETHEMA ALL-AR-03 Trial Including the Use of Propensity Score (PS) Method to Reduce Assignment Bias.

Abstract 322 Introduction:Current therapeutic protocols for adult ALL consider MRD together with the baseline risk factors (age, WBC count, immunophenotype, cytogenetics) and speed in response to therapy for treatment decisions. On the other hand, the systematic use of allogeneic SCT for all adult patients (pts) with Ph- HR-ALL is still a matter of debate. The aim of the prospective study ALL-AR-03 from the Spanish PETHEMA Group was to evaluate the response to a differentiated therapy (chemotherapy or allogeneic SCT) according to early bone marrow blast clearance (<10% blasts in bone marrow assessed on day 14) and MRD levels (assessed by cytofluorometry at the end of induction –week 5- and consolidation therapy –week 17-) in HR Ph- adult ALL patients. Patients and methods:HR ALL included one or more of the following baseline parameters: age 30–60 yr, WBC count >25×109/L and 11q23 or MLL rearrangements. Induction therapy included vincristine, prednisone and daunorubicin for 4 weeks. In pts with slow cytologic response to therapy intensified induction with high dose ARA-C and mitoxantrone was administered. Early consolidation therapy included 3 cycles with rotating cytotoxic drugs including high-dose methotrexate, high-dose ARA-C and high-dose asparaginase. Pts. with slow cytologic response on d14 or MRD level >0.05% after consolidation were assigned to allogeneic SCT (related or unrelated) and those with standard cytologic response on d14 and MRD level <0.05% after consolidation received 3 additional cycles of delayed consolidation (identical to those of early consolidation) followed by maintenance therapy up to 2yr in CR. Results:On June 2009, 235 HR ALL pts were evaluable [mean (SD) age 37(14) yr, 129 males, 155 precursor B-ALL, 80 T-ALL, WBC count 64(96) ×109/L]. Induction death: 20(8%), resistance: 11 (5%), CR: 202 (87%). Slow cytologic response on d14 was observed in 137/186 (74%) pts, MRD<0.1% at the end of induction was observed in 70% of CR patients and MRD<0.05% was shown in 82% of pts at the end of consolidation. By intention-to treat allogeneic SCT was assigned to 51 pts and delayed consolidation and maintenance to 107 pts. 4-yr DFS and OS probabilities were 40±15% and 49±15%, respectively, for pts assigned to SCT and 49±13% and 64±12%, respectively, for those assigned to chemotherapy. For OS the Cox model including PS showed that patients assigned to allogeneic SCT had a risk of death of 1.27 (95%CI 0.68–2.37) compared to that of the pts assigned to chemotherapy. Patients with MRD<0.1% at the end of induction and <0.05% at the end of consolidation showed a 4-yr DFS and OS of 54±16% and 77±12%, respectively vs. 31±29% and 38±32%, respectively for those with MRD≥0.1% after induction and ≥0.05% after consolidation (p=0.04 and 0.006, respectively). By multivariate analysis, including the type of treatment as covariate, age and slow cytologic response were the prognostic factors for CR, MRD level was associated with DFS, and MRD level and WBC count were the main parameters with influence on OS. Conclusions:These results suggest that in HR Ph- adult ALL pts with adequate response to induction and adequate clearance of MDR after consolidation the results of therapy are not hampered by avoiding allogeneic SCT. MRD is the main prognostic factor for CR, DFS and OS. Supported by grants P-EF/07 from FIJC and RD 06/0020/10556 from RETICS, and PI051490 from FIS, Instituto Carlos III. Disclosures:No relevant conflicts of interest to declare.