Key demographics across patients with and without BCA. (A) Prior nonmutually exclusive therapies, most patients had prior HSCT (54.9%), followed by CAR T-cell therapy (39.5%). (B) Percent of patients with BCA before the initiation of LD chemotherapy; most patients had BCA before LD chemotherapy in our cohort (70.4%). (C) Pre–CAR T-cell BCA CD19 cell count; various studies indicate different CD19 thresholds as indicator for BCA. Most patients achieve CD19 values of <50 cells per μL (70.4%). (D) High and low disease burden for patients with and without BCA; relatively similar proportion of patients with and without BCA in each cohort. (E) Prior CAR T-cell vs prior CAR T-cell naïve BCA; relatively similar proportion of patients with and without BCA in each cohort. (F) Percent of MRD-negative CR patients with pre–CAR T-cell BCA; greater percentage of MRD-negative CR patients had BCA (69.4%). Panels A-E describe the full cohort (N = 162). Panel F describes the MRD-negative CR cohort (n = 98). (G) High and low disease burden for patients with and without BCA, using BCA cutoff of <5 cells per μL. (H) Prior CAR T-cell vs prior CAR T-cell naïve BCA, using BCA cutoff of less than 5 cells per μL. BCA as defined by BCA less than 50 cells per μL; high disease burden defined as ≥M2 marrow and low disease burden defined as <M2 marrow. MRD-negative CR, minimal residual disease negative clinical response; ns, not significant.