Real World Chart Review of Blinatumomab to Treat Patients with High Disease Burden of Relapsed or Refractory B-Cell Precursor Acute Lymphoblastic Leukemia

Introduction: Blinatumomab is a bispecific, CD19-directed CD3 T-cell engager (BiTE^®) that activates endogenous cytotoxic T cells to kill target B cells and is FDA-approved for the treatment of relapsed or refractory (R/R) B-cell precursor acute lymphoblastic leukemia (B-ALL). Subgroup analyses of pivotal trials revealed lower response rates and higher risk of cytokine release syndrome (CRS) in blinatumomab recipients with high pre-treatment tumor (B-ALL) burden. It has therefore been hypothesized that cytoreduction prior to blinatumomab initiation may improve response and reduce risk of severe CRS in patients (pts) with high baseline B-ALL burden. We therefore sought to describe pt and disease characteristics at diagnosis, patterns of pre-blinatumomab cytoreduction, and treatment outcomes in pts with high burden of R/R B-ALL treated with blinatumomab at our institution. Methods: We retrospectively reviewed medical records of adult (≥ 18 years-old) pts with morphologic R/R B-cell ALL (i.e. ≥5% BM blasts and/or radiographically evident EM disease) treated with blinatumomab at Memorial Sloan Kettering Cancer Center (MSKCC) between January 2011 and March 2019 and characterized pts with ≥ 50% bone marrow (BM) blasts by morphology or ≥ 15,000 peripheral blood blasts/µL as having "high-burden" B-ALL. CRS and neurologic toxicity (NTX) were graded per Common Terminology Criteria for Adverse Events v5.0. Objectives included describing cytoreductive therapy given pre-blinatumomab and determining rates of NTX and CRS (any grade and grade ≥3) and morphologic complete response (CR) following 1-2 cycles of blinatumomab. Results: We identified 14 pts with high-burden R/R B-ALL prior to blinatumomab. These pts had a median age of 52 years (range, 23 - 69 years) and median BM blasts of 73% (range, 52 - >95%, n=12 pts with evaluable BM). Of these 14 pts, 8 received cytoreductive therapy prior to blinatumomab initiation. Cytoreductive regimens included dexamethasone alone (n=4), cyclophosphamide + dexamethasone (n=2), dexamethasone and vincristine (n=1), or cyclophosphamide + vincristine + dexamethasone (n=1). One pt transitioned to hospice care prior to completing cycle 1 (C1) of blinatumomab and was considered non-evaluable for response. CR was achieved in 6 of the 13 evaluable pts, including 4 of 7 evaluable pts who received cytoreductive therapy and 2 of 6 pts who did not receive cytoreductive therapy. One pt achieved CR in BM but exhibited refractory extramedullary disease. CRS was observed during C1 of blinatumomab in 11/14 pts (grade 1, n=7; grade 2, n=3; grade 3, n=1). The pt with grade 3 CRS had received blinatumomab without cytoreductive therapy. In 4 pts, blinatumomab was temporarily discontinued for management of CRS. NTX of any grade occurred in 4/13 pts during C1, including 1 pt w/grade 3 NTX (depressed level of consciousness), and was reversible in all cases; the pt with grade 3 NTX had full resolution of symptoms following brief interruption of blinatumomab and administration of dexamethasone. Conclusions: Real-world clinical experience with blinatumomab in pts with high-burden B-ALL at a single institution suggested an efficacy and safety profile comparable to what has been reported in the overall population in clinical trials. Compared to published clinical trial experience, rates and severity of CRS following blinatumomab were similar and rates of NTX appeared slightly higher in this small series. Administration of cytoreductive therapy prior to blinatumomab for pts with high-burden B-ALL appears safe, with no additional toxicities. Larger studies will be required to assess whether pts with high-burden B-ALL treated (vs not treated) with cytoreductive therapy prior to blinatumomab exhibit significantly higher rates of CR.