Efficacy and Safety of Blinatumomab in Asian Adults with Relapsed/Refractory B-Precursor ALL

Introduction: Blinatumomab is a bispecific T-cell engager (BiTE^®) targeted immuno-oncology therapy with dual specificity for cluster of differentiation (CD) 19 and CD3 that redirects the patient's CD3-positive cytotoxic T cells to lyse CD19-positive malignant cells. Global studies have evaluated blinatumomab in patients with advanced Philadelphia chromosome-negative relapsed/refractory acute lymphoblastic leukemia (Ph- R/R ALL). In the global phase 3 TOWER study, blinatumomab monotherapy vs standard-of-care chemotherapy resulted in a significantly higher rate of complete remission (CR)/CR with partial hematologic recovery of peripheral blood counts (CRh)/CR with incomplete hematologic recovery of peripheral blood counts (44% vs 25%; P < 0.001) and longer median overall survival (7.7 vs 4.0 months; P = 0.01) (Kantarjian H, et al. NEJM. 2017;376:836-47). There are limited data on the efficacy and safety of blinatumomab in Asian patients, whose immunologic genetic background may differ from other patient populations. Therefore, we conducted a patient-level pooled analysis of the efficacy and safety of blinatumomab in 45 Asian adult patients with Ph- R/R ALL-19 from the blinatumomab arm of TOWER (NCT02013167) and 26 from a phase 1b/2 study in Japanese adults (NCT02412306).

Methods: Patients in both studies were ≥ 18 years old and had Ph- R/R ALL, > 5% blasts, Eastern Cooperative Oncology Group performance status 0-2, and no central nervous system pathology. Patients received a maximum of 2 cycles of induction blinatumomab for 4 weeks by continuous intravenous infusion (cycle 1/week 1: 9 μg/day; cycle 1/weeks 2-4: 28 μg/day; subsequent cycles: 28 μg/day) followed by 2 weeks of no blinatumomab (each 6-week cycle). Responders (≤ 5% bone marrow blasts within 2 induction cycles) received blinatumomab 28 μg/day up to a maximum of 5 induction/consolidation cycles. In TOWER, patients who continued morphologic remission received up to 12 months of maintenance therapy. Patients could undergo stem cell transplantation at any time following the first treatment cycle.

Results: Of the 45 Asian patients enrolled (26 female; median [range] age, 43 [18-75] years; prior hematopoietic stem cell transplantation, 20 [44.4%]; ≥ 1 prior salvage therapy, 30 [66.7%]), 44 received at least 1 cycle of blinatumomab 9-28 μg/day. Responses in the first 12 weeks of treatment (CR/CRh and minimal residual disease response) are shown in the Table. The Kaplan-Meier (KM) median overall survival time was 11.9 (95% CI: 9.9-17.1) months, and the KM median relapse-free survival time was 8.9 (95% CI: 3.8-10.7) months; median overall survival in the blinatumomab arm of TOWER was 7.7 months. Forty-one (93.2%) patients had grade ≥ 3 treatment-emergent adverse events (TEAEs), and 5 (11.4%) had fatal AEs. Grade ≥ 3 events TEAEs of interest included neurologic events (4.5%), cytokine release syndrome (2.3%), cytopenias (6.8%), and infections (20.5%).

Conclusions: The safety and efficacy of blinatumomab in Asian patients were comparable with previous global studies with similar disease response rates and a favorable safety profile with no new safety signals.

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