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363 A Randomized Phase 3 Trial of Blinatumomab Vs. Chemotherapy As Post-Reinduction Therapy in Low Risk (LR) First Relapse of B-Acute Lymphoblastic Leukemia (B-ALL) in Children and Adolescents/Young Adults (AYAs): A Report from Children’s Oncology Group Study AALL1331

Program: Oral and Poster Abstracts
Type: Oral
Session: 614. Acute Lymphoblastic Leukemias: Therapies, Excluding Transplantation and Cellular Immunotherapies I
Hematology Disease Topics & Pathways:
Biological, ALL, Lymphoid Leukemias, Clinical Trials, Bispecific Antibody Therapy, Clinical Research, Clinically Relevant, Diseases, Therapies, Lymphoid Malignancies
Sunday, December 12, 2021: 10:00 AM

Patrick A. Brown, MD1, Lingyun Ji2*, Xinxin Xu3*, Meenakshi Devidas, PhD4*, Laura Hogan, MD5, Teena Bhatla6*, Michael Borowitz, MD, PhD7, Elizabeth A. Raetz, MD8, Lia Gore, MD9, James A. Whitlock, MD10, Stephen P. Hunger, MD11 and Mignon L. Loh, MD12

1Division of Pediatric Oncology, Sidney Kimmel Comprehensive Cancer Center, Johns Hopkins University, Baltimore, MD
2Department of Population and Public Health Sciences, Keck School of Medicine, University of Southern California, Los Angeles
3Children's Oncology Group, Monrovia, CA
4Global Pediatric Medicine, St Jude Children's Research Hospital, Memphis, TN
5Stony Brook Children's, Stony Brook, NY
6Children's Hospital of New Jersey at Newark Beth Israel, Newark, NJ
7Departments of Pathology and Oncology, Johns Hopkins Hospital, Baltimore, MD
8Department of Pediatrics and Perlmutter Cancer Center, NYU Langone Health, New York, NY
9Section of Hematology, Oncology, and Bone Marrow Transplantation, University of Colorado and Children’s Hospital, Aurora, CO
10Division of Haematology/Oncology, The Hospital For Sick Children, Toronto, ON, Canada
11Department of Pediatrics, Division of Oncology and the Center for Childhood Cancer Research, CHILDREN'S HOSPITAL OF PHILADELPHIA, Philadelphia, PA
12Department of Pediatrics, Division of Pediatric Hematology/Oncology, University of California Benioff Children’s Hospital, San Francisco, CA

Standard treatment of children and AYAs with LR first relapse of B-ALL [LR defined as bone marrow with or without extramedullary (BM±EM) relapse ≥36 months or isolated EM (IEM) relapse ≥18 months from initial diagnosis, and low (<0.1%) BM minimal residual disease (MRD) at the end of reinduction chemotherapy] consists of approximately 2 years of standard chemotherapy without hematopoietic stem cell transplant. The objective of this study was to compare survival [primary: disease-free (DFS); secondary: overall (OS)] of LR first relapse B-ALL patients aged 1-30 years randomized following reinduction chemotherapy (Block 1 of UKALLR3/mitoxantrone arm) to receive either two intensive chemotherapy blocks (Blocks 2 and 3 of UKALLR3) followed by continuation and maintenance chemotherapy of UKALLR3 (chemotherapy control) vs. the same except with integration of three 4-week cycles of blinatumomab, one replacing Block 3 chemotherapy and two added during continuation and maintenance (blinatumomab experimental). All patients with central nervous system (CNS) leukemia at relapse (isolated or combined with BM relapse) received additional intensified CNS-directed chemotherapy (intrathecal and systemic) and 1800 cGy of cranial radiation during maintenance. Patients with testicular leukemia at relapse that persisted after Block 1 reinduction received 2400 cGy testicular radiation during Block 2.

A total of 255 LR patients were randomized: Blinatumomab: 127; Chemotherapy: 128. Selected baseline characteristics are shown in Table 1. With median follow up of 2.9 years (data cut-off 12/31/20), the intent-to-treat (ITT) 4-year DFS (%±standard error) was 61.2±5.5% for blinatumomab vs. 48.2±6.0% for chemotherapy (p=0.15, 1-sided stratified log-rank test per pre-specified statistical plan). The 4-year OS was 91.6±3.0% for blinatumomab vs. 83.3±4.5% for chemotherapy (p=0.096).

Striking differences in DFS and blinatumomab efficacy were noted according to site of first relapse (Figure 1). For BM±EM relapses, 4-year DFS was 74.0±6.4% for blinatumomab vs. 51.8±7.9% for chemotherapy (p=0.016), and 4-year OS was 96.6±2.5% for blinatumomab vs. 84.4±5.6% for chemotherapy (p=0.013). Significant predictors of DFS in Cox multivariable regression for BM±EM relapses included treatment arm, age at relapse, and time from diagnosis to first relapse (Table 2). For IEM relapses, 4-year DFS was 34.2±8.6% for blinatumomab vs. 39.3±8.5% for chemotherapy (p=0.73), and 4-year OS was 81.7±7.0% for blinatumomab vs. 80.8±7.2% for chemotherapy (p=0.61). The only predictor of DFS in IEM patients was site of first relapse [hazard ratio for testes vs. CNS 0.19 (0.04-0.87), p=0.015]. The difference in DFS between BM±EM and IEM patients was driven by excess of second relapse in isolated CNS relapse patients (Table 3). Of 64 CNS relapses, 39 (61%) had a second relapse, of which 28 (72%) were also isolated CNS, with no difference by treatment arm. Of the 191 remaining patients, 35 (18%) had a second relapse [13 (14%) blinatumomab (6 BM±EM, 7 IEM), 22 (23%) chemotherapy (15 BM±EM, 7 IEM)].

Blinatumomab cycle 1 was better tolerated than Block 3 chemotherapy, with lower rates of CTCAEv4 grade ≥3 febrile neutropenia (3% vs. 47%, p<0.001), infections (5% vs. 51%, p<0.001), anemia (12% vs. 57%, p<0.001) and mucositis (1% vs. 7%, p=0.018). The rate of selected blinatumomab-related adverse events (AEs) in blinatumomab cycles 1/2/3 (all grades) were: Cytokine release syndrome (CRS) 12%/7%/7%, seizure 3%/1%/3%; other neurotoxicity (e.g., cognitive disturbance, tremor, ataxia, dysarthria) 19%/9%/5%. All blinatumomab-related AEs were fully reversible.

In conclusion, for children and AYA patients with LR first relapse of B-ALL, while there was no significant difference in outcome for the entire population, the blinatumomab arm was superior to the standard chemotherapy arm for patients with BM±EM relapse, establishing this regimen as a new standard therapy for these patients. The blinatumomab arm was not superior in IEM relapse. Isolated CNS relapse patients had a strikingly high relapse rate on both arms; better treatments are urgently needed for this subset.

Disclosures: Brown: Novartis: Membership on an entity's Board of Directors or advisory committees; Takeda: Membership on an entity's Board of Directors or advisory committees; Amgen: Membership on an entity's Board of Directors or advisory committees; Kura: Membership on an entity's Board of Directors or advisory committees; KIte: Membership on an entity's Board of Directors or advisory committees. Borowitz: Amgen, Blueprint Medicines: Honoraria. Raetz: Celgene: Other: DSMB member; Pfizer: Research Funding. Gore: Amgen: Current equity holder in publicly-traded company, Membership on an entity's Board of Directors or advisory committees; Janssen: Membership on an entity's Board of Directors or advisory committees; Kura Oncology: Membership on an entity's Board of Directors or advisory committees; Mirati: Current equity holder in publicly-traded company; Novartis: Consultancy, Membership on an entity's Board of Directors or advisory committees; OnKure: Membership on an entity's Board of Directors or advisory committees; Pfizer: Membership on an entity's Board of Directors or advisory committees; Roche/Genentech: Consultancy; Sanofi Paris: Current equity holder in publicly-traded company. Whitlock: Amgen; Jazz Pharmaceuticals: Honoraria; Novartis: Research Funding; Sobi Pharmaceuticals: Consultancy. Hunger: Amgen: Current equity holder in publicly-traded company. Loh: MediSix therapeutics: Membership on an entity's Board of Directors or advisory committees.

OffLabel Disclosure: Blinatumomab, used as post-reinduction consolidation without regard to MRD

*signifies non-member of ASH