Reduced-Dose Chemotherapy Followed By Blinatumomab As Induction Therapy in Treatment of Newly Diagnosed Philadelphia Chromosome-Negative B-Cell Precursor Acute Lymphoblastic Leukemia - Interim Results from a Multicenter, Single-Arm, Phase 2 Study

Introduction: Although intensive pediatric chemotherapeutic regimens have shown good efficacy in the treatment of Philadelphia Chromosome-negative (Ph-negative) B-cell precursor acute lymphoblastic leukemia (BCP-ALL) in adults, the high incidence of chemotherapy-related toxicities limits their use. Blinatumomab, a CD3/CD19 bispecific T-cell antibody, has shown high efficacy in relapsed/refractory or minimal residual disease (MRD) positive BCP-ALL; however, the efficacy of single-agent blinatumomab does not meet the treatment needs of adult patients. Therefore, combining low-intensity chemotherapy with blinatumomab could be a better induction regimen for newly diagnosed adult patients with BCP-ALL.

Methods: This multicenter, single-arm, phase 2 trial (NCT05557110) enrolled adult patients (aged 15-59 years) with newly diagnosed Ph-negative BCP-ALL. The induction regimen comprised reduced intensity chemotherapy (idarubicin 8 mg/m² on day 1, vindesine 4 mg on day 1, and dexamethasone 9 mg/m²/day from day 1-7) followed by 2 weeks of blinatumomab (9 ug/day from day 8-14, 28 ug/day from day 15-21). The primary endpoint was to assess the overall response rate (ORR=complete remission [CR] + CR with partial hematologic recovery [CRh] + CR with incomplete hematologic recovery [CRi]) of this induction regimen. Secondary endpoints were MRD negativity (<1x10^-4 by flow cytometry), event-free survival (EFS), overall survival (OS) and safety. Bone marrow evaluation and one intrathecal injection chemotherapy were performed on day 22±2. Patients not achieving ORR continued blinatumomab for another 2 weeks (28 ug/day from day 1-14), followed by bone marrow re-evaluation. Consolidation therapy was given after achieving ORR with recommended multidrug combination chemotherapy (including high-dose methotrexate or cytarabine combined with asparaginase) or alternating with blinatumomab (28 ug/day for 28 days). If allogeneic hematopoietic stem cell transplantation (allo-HSCT) is not performed, consolidation therapy needs at least 4 courses before 2 years of maintenance therapy.

Results: Interim results are presented here. By July 6, 2023 (data cut-off), 25 patients were enrolled with a median age of 42 years (range: 15-53); 68% were females. The Eastern Cooperative Oncology Group Performance Status score ranged from 0-1. Eight (32.0%) patients had poor cytogenetic risk factors, including 3 with P2RY8::CRLF2, 2 with hypodiploidy, 2 with KMT2A rearranged and 1 with alterations of IKZF1 (Table 1).

The bone marrow evaluation done in 19 patients on day 8 prior to blinatumomab treatment showed that none of the patients had got ORR. All 21 (100%) patients evaluable for the primary endpoint attained CR/Cri - 19 at the end of 2 weeks of blinatumomab and the remaining 2 after another 2 weeks of blinatumomab (Table 2). The MRD negativity rate was 90.5% (19/21) after 2 weeks of blinatumomab which increased to 95.5% (20/21) after another 2 weeks of treatment with blinatumomab. In 21 patients evaluated for safety, blinatumomab-related cytokine release syndrome was reported in 10 (47.6%) patients (grade 1: n=6, grade 2: n=3 and grade 3: n=1). No incidence of neurotoxicity was reported. Febrile neutropenia was reported in 4 (19%) patients (all ≥grade 3). The non-hematological AEs reported were fever in 7 (33.3%) patients (any grade), increased ALT in 10 (47.6%) patients (any grade) and infections in 4 (19%) patients, including pneumonia in 2 and sepsis in 2 (all ≥grade 3). The median duration of neutrophil deficiency (<0.5×10⁹/L) and platelet deficiency (<20×10⁹/L) during induction therapy was 9 days (range: 0-20) and 1 day (range: 0-18), respectively.

The median follow-up time was 4 months and no relapse or leukemia-related deaths were observed. The median EFS and OS were not yet reached. All enrolled patients are alive except one who died of infection after multidrug combination consolidation chemotherapy. The median cycles for consolidation were 2 (range: 1-5) with 3 patients undergoing allo-HSCT.

Conclusion: These preliminary results indicate that the reduced intensity chemotherapy followed by blinatumomab is an effective regimen in adults with newly diagnosed Ph-negative BCP-ALL, resulting in favorable response rates, deep remission, and low-grade treatment-related AEs. These promising findings may provide a rationale for integrating blinatumomab into future induction therapy recommendations.