Citations

Abstract Background Standardizing beam modeling in the treatment planning system is challenging due to machine‐specific configuration variations. Because of the proton therapy system (PTS) complexity and continuous development, there is no vendor's representative (“golden”) beam data like in LINACs at this stage. Purpose The primary goal of this study is to create a PTS‐specific repository of source model parameters and beam commissioning data for scanning proton therapy treatment planning systems and establish a set of reference values with associated bands of variations for this data. Methods We conducted a survey of 31 PTSs at 27 proton therapy centers to gather beam commissioning source model parameters used in their treatment planning system, ensuring a diverse selection of PTSs from major vendors: Hitachi, IBA, Varian, and Mevion. For each proton therapy center, we collected (i) beam meterset calibration in protons per MU, (ii) in‐air spot size at isocenter in terms of standard deviation in x‐ (crossline, σ x ) and y‐ (inline, σ y ) directions, (iii) in‐air angular spread at isocenter in x‐direction (θ x ) and y‐direction (θ y ) and (iv) distal falloff. For each PTS, we plotted each parameter as a function of nominal energy and performed polynomial regression analysis with optimal model selection based on Akaike Information Criterion. We calculated intraclass correlation coefficients (ICC) to quantify inter‐PTS variability and generated uncertainty bands representing standard deviations across PTSs for each parameter. Additionally, we computed percentage deviations of each individual PTS from the overall multi‐vendor mean to identify systematic vendor‐specific patterns and outliers across the 31 total PTSs analyzed. Results Multi‐vendor beam parameter analysis across 31 PTSs revealed systematic vendor‐specific patterns in inter‐PTS consistency and energy dependencies. Beam meterset calibration demonstrated excellent inter‐PTS consistency across most vendors (ICC: Varian ProBeam ≈ 0, IBA Proteus ONE = 0.006, Mevion S250i with HYPERSCAN = 0.015), with IBA Proteus PLUS systems showing moderate variation (ICC = 0.156 for the dedicated nozzle, ICC = 0.248, for the universal nozzle). Spot size and angular spread variability were highly vendor‐dependent, ranging from excellent consistency in IBA Proteus ONE to substantial variation in IBA Proteus PLUS with the universal nozzle (angular spread ICC = 0.566). Distal falloff maintained excellent consistency across all vendors (ICC < 0.023), indicating reliable energy spread characteristics. Uncertainty band analysis revealed characteristic energy‐dependent patterns, with most systems showing larger uncertainties at lower energies for spot size and angular spread, while IBA Proteus PLUS with the universal nozzle exhibited the largest uncertainty bands overall. Percentage deviation analysis demonstrated vendor‐specific clustering patterns, with some systems showing systematic positive or negative deviations from the multi‐vendor mean. Conclusions The reference data provided in this work will help to cross‐check the beam model during treatment planning system commissioning. Furthermore, this information is useful for Monte Carlo applications and research, where beam characteristics are required to set up phase space parameters, thereby avoiding the need to model the entire PTS. Finally, the results of this study will have indispensable educational value by providing valuable insights into the characteristics and capabilities of different PTSs.

Abstract Context Recent studies suggest glucagon-like peptide receptor-1 agonists (GLP-1RA) and glucose-dependent insulinotropic polypeptide (GIP) may contribute to altered calcium metabolism. Objective This study examines the association between GLP-1RA/GIP-RA use and risk of post-thyroidectomy hypocalcemia. Methods This propensity-matched cohort study utilized the TriNetX Platform to analyze adult patients who underwent total thyroidectomy (2010 to 2024). The intervention cohort included patients with a GLP-1RA or GIP-RA prescription 1 year before thyroidectomy; the control group had no GLP-1RA/GIP-RA history. Propensity score matching controlled for demographics and relevant clinical covariates. Primary outcomes included risk of hypocalcemia at 0-1 month, 1-6 months, and 6-12 months after surgery. Using Poisson regression, odds ratios were reported (alpha = 0.05). Results Among 70 665 patients, 1759 (2.59%) received a GLP-1RA or GIP-RA. Each matched cohort contained 1732 patients with similar preoperative parathyroid hormone or calcium levels. The GLP-1RA/GIP-RA cohort had a 12% lower risk of hypocalcemia from 0 to 1 month after surgery (relative risk [RR] 0.88; 95% CI: 0.81-0.97). In the sensitivity analysis considering postoperative calcitriol supplementation, recipients with GLP-1RA/GIP-RAs use were less likely to develop hypocalcemia in the month after surgery (RR 0.84; 0.74-0.96), as were those with GLP-1RA/GIP-RAs who never received calcitriol in the month after surgery (RR 0.81; 0.72-0.90). Under subgroup analysis, semaglutide was the sole agent associated with a reduced risk of hypocalcemia. Conclusion Patients with a history of GLP-1RA/GIP-RA use may experience a lower risk of short-term hypocalcemia after thyroidectomy, suggesting personalized supplementation strategies may be required for this population.

Importance Breast cancer treatment is associated with cancer-related cognitive impairment (CRCI). However, the association of endocrine therapy (ET) vs chemotherapy plus endocrine therapy (CET) with CRCI is poorly understood. Objective To compare patient-reported CRCI between women with breast cancer treated with ET vs CET and to consider whether menopausal status may be associated. Design, Settings, and Participants This was a prespecified secondary analysis of RxPONDER (SWOG S1007), a multinational phase 3 randomized clinical trial of more than 5000 women with hormone receptor−positive ERBB2 -negative (formerly HER2 -negative) breast cancer with 1 to 3 involved lymph nodes and Oncotype DX (21-gene recurrence score) of 25 or less. Participants were enrolled from February 2011 to September 2017, with results first reported in December 2020. Participants were randomly assigned to CET or ET, with ongoing follow-up. This secondary analysis assessed cognitive function using the Patient-Reported Outcomes Measurement Information System Perceived Cognitive Function Concerns (PCF) questionnaire at baseline, 6, 12, and 36 months. Data were analyzed from July 2022 to August 2025. Intervention Random assignment to CET or ET. Main Outcomes and Measures Mean PCF standardized (T) scores by menopausal status over time using generalized estimating equations analysis for continuous outcomes. Results Of the 568 patients who completed the baseline questionnaire and were included in the analysis, 139 (24%) were premenopausal (median [range] age, 47.8 [28.0-56.3] years) and 429 (76%) were postmenopausal (median [range] age, 62.3 [37.3-87.6] years). Among the 274 (48%) who received CET and the 294 (52%) who received ET alone, CET was determined to have a greater negative association with patient-reported CRCI in both the pre- and postmenopausal participants during the 36-month follow-up. In the ET alone group, PCF scores for premenopausal participants decreased from baseline to 6 and 12 months (53.53, 51.51, and 51.72, respectively) but recovered to baseline (54.36) at 36 months. For postmenopausal participants, mean PCF scores were essentially stable (51.72, 51.13, 51.11, and 51.70, respectively); however, in the CET group, PCF scores for both pre- and postmenopausal participants decreased from baseline to 6 and 12 months (premenopausal, 52.84, 49.27, 48.04; postmenopausal, 50.65, 48.39, 47.13, respectively) and did not return to baseline at 36 months (premenopausal, 49.25; postmenopausal, 48.44). The difference in longitudinal mean PCF scores over time between CET and ET groups was −3.02 (95% CI, −5.33 to −0.72; P = .01) for premenopausal and −2.37 (95% CI, −3.92 to −0.82; P = .003) for postmenopausal participants. Conclusions and Relevance This secondary analysis of the RxPONDER found that CET had a greater negative association with patient-reported CRCI compared to ET alone in both pre- and postmenopausal participants over a 36-month follow-up period. Interventions to prevent or treat CRCI are needed to improve the long-term quality of life of these patients treated with chemotherapy. Trial Registration ClinicalTrials.gov Identifier: NCT01272037

Abstract Chimeric antigen receptor (CAR) T-cell therapy has demonstrated remarkable response rates in relapsed/refractory aggressive B-cell non-Hodgkin's lymphoma. However, durable remissions occur in only 40% of treated patients, highlighting mechanisms of therapeutic resistance and immune escape. While cytotoxicity is principally executed by CAR T-cells, monocytes shape CAR-T cell efficacy and orchestrate cytokine-driven immunity. In this study, we defined distinct metabolic profiles of T-cell and monocyte subsets based on clinical response. Single-cell RNA sequencing (scRNA-seq) and T-cell receptor sequencing (scTCR-seq) were performed on peripheral blood mononuclear cells at three timepoints: before lymphodepletion (BL), at peak CAR-T expansion (PK), and one-month post-infusion (M1). Data were processed with CellRanger v7.0.1 and analyzed with the immunopipe pipeline (Wang et al., 2025). Seurat v4.3.0 was utilized for unsupervised hierarchical clustering analysis; subsets identified included classical monocytes (CM), intermediate monocytes (IM), non-classical monocytes (NM), and monocytic myeloid derived suppressor cells (mMDSC). Metabolic profiles were compared across patients achieving ≥6-month complete remission (CR, n=16), primary refractory disease (PD1, n=4), or relapsed after a prior response (PD2, n=12). A total of 107035 T cells and 129981 monocytes from 77 serial samples in 32 patients were analyzed. CR patients had a higher T-cell:monocyte ratio than PD1/PD2 at all time points, especially at BL and PK (BL 1.2 vs 0.4, p=0.011; PK 1.3 vs 0.3, p=0.027). Clinical responses were compared with metabolic pathway analysis and identified oxidative phosphorylation (OXPHOS) as the dominant pathway. OXPHOS was consistently enriched in PD cohorts across T-cell subsets, particularly in PD1 vs CR at BL (mucosal-associated invariant T-cell (MAIT) and T peripheral memory (Tpm)), and at PK (CD4/CD8 memory precursor effector cells (MPEC) and activated MPECs (MPECa), CD4 T-helper 1 proliferating (Th1p), CD4 Th2 activated (Th2a), regulatory T-cell (Treg), CD8 naive senescent (CD8NS), CD8 T effector memory (Tem) tumor recirculating (TR), CD8 Tpm, CD8 T resident memory (Trm) TR and MAIT Tpm). By M1, OXPHOS enrichment in CD4/CD8MPECa, CD4Th2a, CD8NS, CD8TemTR reversed, now predominant in CR although CD8Tpm and CD8TrmTR remained enriched in PD1. In the monocyte subsets at BL, PD2 showed OXPHOS enrichment in CD163+ monocytes (mono), IM IL1, mMDSC SIRPA, mMDSC TGFβ, and CM IL6 subsets compared to PD1 and CR, while PD1 showed OXPHOS enrichment in IM CD38, CM TGFβ, and mMDSC HIF1A vs CR and PD2. This persisted at PK. By M1, the pattern reversed and mirrored that of T-cells, with CR patients showing OXPHOS enrichment in CD163+mono, CM IL6, CM TGFβ, IM CD38, mMDSC HIF1A, mMDSC SIRPA and mMDSC TGFβ, and additionally in CM EMT, CM p53, NM, NM CD36 vs PD1/PD2. Glycolysis/gluconeogenesis (GLY) was also enriched across subsets. In T-cells, PD1 vs CR showed GLY enrichment in CD4Th2a, CD8Tpm, CD8Tpm proliferating and MAIT Tpm at PK. In monocytes, GLY was enriched in PD1/2 vs CR at BL (CD163+mono, CM IL6) and PK (CD163+mono, IM CD18, mMDSC SIRPA). By M1, GLY metabolism was enriched in CR vs PD1/PD2 in CD163+mono, CM IL6, mMDSC SIRPA. Additional GLY enriched subsets at CR vs PD1 included CM, CM p53, EMT, IM CD38, IM IL1, mMDSC HIF1A, NM, NM CD36. Inositol phosphate metabolism (IP) was predominantly enriched in PD2 vs CR at BL (CD8NS, CD8Tcm, CD8Tpm activated), PK (CD4Th2, CD8NS, CD8Tem TR, CD8Tpm proliferating, γδT Tem) and M1 (CD4/CD8 MPECa, CD4 Th1/Th2, CD8NS, CD8Tpm, CD8 Tpm proliferating, Treg and MAIT Tpm). Notably, Treg was the only T-cell subset enriched for IP at PK in CR vs PD1/PD2. Additionally, the TCA cycle was enriched in PD1 Tregs and Th2 cells at BL and PK vs CR/PD2. A higher T-cell:monocyte ratio in CR vs PD1/PD2 supports prior evidence that elevated pre-lymphodepletion lymphocyte:monocyte ratios predict better outcomes. We identified distinct metabolic signatures in T-cells and monocytes between CR and PD1/PD2. OXPHOS enrichment in T-cells and monocytes at M1 in CR patients may reflect oxidative programming as a hallmark of sustained anti-tumor immunity. Conversely, GLY enrichment in PD1 T-cells at PK may reflect short-lived effector states lacking persistence. Overall, these findings highlight metabolic profiling as a promising predictive biomarker and therapeutic programming target to enhance CAR T-cell outcomes.

Abstract Chimeric Antigen Receptor (CAR) T cell therapy is a transformative treatment for hematologic malignancies. However, ex vivo autologous CAR T cell manufacturing presents substantial logistical and clinical challenges. Direct in vivo CAR-T cell engineering offers a new paradigm for CAR T delivery. We recently developed the CD3-targeted lentiviral vector LV-169 which can deliver a CAR transgene to resting niche-resident T cells in lymphoid tissues. LV169 is pseudotyped with a mix of chimeric and nonchimeric VSV-G proteins detargeted (blinded) from the natural LDL receptor and re-targeted to T cells through the display of a CD3-specific scFv. Here we demonstrate that LV169 can specifically deliver a functional aBCMA-CAR transgene to resting human T cells in PBMC cultures from the healthy volunteers and from multiple myeloma patients. For clinical translation, we selected an αBCMA-CAR construct comprising a fully human single heavy chain nanobody linked to 41BB and CD3z cytoplasmic signaling domains. Human T cells expressing this CAR construct have low tonic signaling and efficiently kill BCMA-positive myeloma target cells with similar or lower associated cytokine release compared to a clinically relevant benchmark BCMA-CAR. To further improve LV169 and to minimize CAR protein incorporation in the LV envelope which may lead undesirably to myeloma cell transduction, we placed the CAR transgene under a T-cell specific Lck promoter in reverse orientation relative to the 5' LTR. The transcriptional activity of the Lck promoter was comparable to that of a constitutive EF1a promoter in primary T cells and, in contrast to EF1a had minimal activity in a variety of other tested cell types including the HEK293T producer cell line and the THP-1 monocytic cell line. Western blotting confirmed the absence of CAR protein in LV particles (LVP) generated using the Lck promoter-driven reverse orientation construct. In contrast, high levels of CAR protein were detected in LVP generated using the parental EF1a promoter-driven construct. The LV-incorporated CAR protein mediated off-target gene delivery to BCMA-positive myeloma cells. The therapeutic efficacy of intravenously administered LV169 LV particles carrying BCMA-CAR constructs was tested in the OPM-2 human multiple myeloma xenograft model. NSG mice with knockout of MHC-I and MHC-II, and with advanced disseminated OPM-2-Luc tumors were engrafted with human PBMC one week prior to intravenous LV169-BCMA-CAR administration. Mice were treated with single intravenous injection of LV169 at different doses 3 weeks after tumor engraftment. OPM-2-Luc tumor burden was monitored by regular luciferase imaging. All treated mice cleared their tumors within 28-days following LV administration and the rate of clearance was correlated to the LV particle dose. Even at the 4e8 dose level (by p24) tumors were completely cleared. Eighty four days post-treatment the treated mice remained tumor-free and resisted re-challenge with OPM-2 tumor cells. Circulating CAR-T cells, monitored by flow cytometry, became detectable by 14 dpi and peaked between 21-35 dpi. Following tumor clearance, the number of circulating CAR-T cells declined dramatically. The treatment was well tolerated and analysis of cytokines associated with CAR-T cell cytotoxicity confirmed the absence of a severe cytokine storm. IFNγ was the only cytokine which was elevated during the expansion period of CAR-T cells, while IL-2, IL-6, TNFα and GM-CSF were barely detectable. In summary the characteristics of our new developed LV169-based platform make it suitable for further clinical translation which is underway.

Abstract Introduction: Cilta-cel is a BCMA-directed CAR T-cell therapy that has shown remarkable efficacy in patients with RRMM. As real-world (RW) experience with cilta-cel continues to expand, and with the recent FDA guidance reducing the recommended proximity to the CAR T center from four to two weeks post-infusion, there is growing interest in identifying patients at low risk for severe early complications who may be safely managed in the outpatient setting and potentially ‘discharged’ home earlier. Methods Data were collected from 769 patients with RRMM treated with cilta-cel at 15 institutions in the U.S. via the Multiple Myeloma Immunotherapy Consortium.Logistic regression was used to identify predictors of patients who could be managed in the outpatient setting (low-risk group). Based on expert consensus within the Consortium, low-risk patients were defined as: grade ≤1 CRS, no ICANS, and no IEC-HS. The remaining patients were categorized as high-risk. We evaluated baseline characteristics with missingness &lt; 20% as predictors, including age, sex, race, and ethnicity, ECOG performance status (PS) at time of lymphodepletion (LD), extramedullary disease, bone marrow plasma cell (BMPC) percentage, high-risk cytogenetics, bridging therapy including response, penta-refractory status, number of prior lines of therapy, prior anti-BCMA therapy, baseline C-reactive protein (CRP), and baseline ferritin. The cohort was restricted to patients with complete data on all predictors (n=455) and split into a training and testing cohort (80/20 split, n=364/91). Bidirectional stepwise regression was used to build the predictive model using variables with significance of p&lt;0.15 selected for entry. The best model was selected based on the AIC (Akaike Information Criterion) and a significance level of p&lt;0.05. Results Among the 455 patients with complete data included in the final model, 290 (64%) were categorized as low-risk and 165 (36%) as high-risk. Compared to the low-risk group, high-risk patients were more likely to have an ECOG PS ≥2 at time of LD (20% vs 9%, p&lt;0.001), high-risk cytogenetics (47% vs 35%, p=0.009), and penta-refractory disease status (34% vs 24%, p=0.031). High-risk patients also had a higher median BMPC percentage (15% vs 5%, p&lt;0.001), and higher baseline pre-LD CRP and ferritin. Overall response rates were high, at 95% vs 90% (p=0.047) for the low vs high risk groups, with complete response or better achieved in 73% vs 66% of patients, respectively (p=0.14). With a median follow-up of approximately 11 months, median progression-free survival was not reached (95% CI: 27-NA) in the low-risk group and 18.2 months (95% CI: 13.1-NA) in the high-risk group. In terms of safety, non-ICANS neurotoxicity (NINT) occurred less frequently in the low-risk group (6.6% vs 13%, p=0.015). Specifically, Parkinsonism was observed in 1.7% vs 6.1% (p=0.013), and cranial nerve palsy in 4.5% vs 5.5% (p=0.7), respectively. Non-relapse mortality (NRM) was lower in the low-risk group (4.2%) compared to the high-risk group (14%; p &lt; 0.001). The most common causes of NRM in the low- and high-risk groups were acute toxicities (0% vs 36%, including CRS, IEC-HS, and ICANS), delayed toxicities (0% vs 8%, including colitis, NINT, and Parkinsonism), infections (50% vs 48%), and other unrelated causes (50% vs 8%). The best model to predict low-risk patients that could be managed in the outpatient settingincluded BMPC percentage and ECOG PS at LD. In the training cohort, patients with a higher pre-LD BMPC percentage and an ECOG PS ³2 were less likely to be in the low-risk group(OR per 1-unit change in BMPC percentage = 0.99, 95% CI=0.98-0.99, p&lt;0.001 and OR for ECOG PS 2-4 = 0.38, 95% CI=0.20-0.72, p=0.003). The AUC for this model was 0.663 in the training cohort and 0.659 in the testing cohort. Conclusion In this large, multi-institutional cohort of patients with RRMM treated with cilta-cel, we identified clinical factors associated with lower risk for early severe toxicities, supporting outpatient administration and the potential for earlier discharge in selected patients, particularly those who are fit and have low disease burden. Our findings provide a practical framework to guide risk stratification and outpatient CAR T management strategies, particularly in light of evolving regulatory guidance and growing RW experience with cilta-cel.

Abstract Introduction: Patients with triple-class exposed (TCE) relapsed/refractory multiple myeloma (RRMM) have historically experienced poor clinical outcomes, prompting the development of novel therapeutic options. Idecabtagene vicleucel (ide-cel) was the first chimeric antigen receptor (CAR) T cell therapy approved for this population, while teclistamab became the first approved bispecific antibody. Both target B-cell maturation antigen (BCMA) and are increasingly used in real-world (RW) settings. Most comparative evidence to date is derived from single-arm clinical trials with cross-trial adjustments. RW studies offer an opportunity to directly compare these therapies and assess their relative effectiveness in routine clinical practice. Methods: We conducted a comparative effectiveness analysis of ide-cel and teclistamab in patients with TCE RRMM using RW data from the United States Flatiron Health electronic health record-derived, deidentified database (January 2011 to April 2025 data cut). Adults who received either index therapy at any line of treatment after becoming TCE (ie, previously exposed to an immunomodulatory agent, a proteasome inhibitor, and an anti-CD38 monoclonal antibody) were included. Exclusion criteria were prior exposure to CAR T cell therapy, bispecific antibodies, or belantamab mafodotin; absence of index treatment; or lack of post-index follow-up. Index dates (T0) represent the date of infusion for ide-cel and the start of treatment for teclistamab. Seventeen prognostic covariates were selected a priori based on published rankings and used to balance treatment groups via inverse probability of treatment weighting (IPTW) with average treatment effect weights. Cox proportional hazards models were used to estimate unadjusted and IPTW-adjusted HRs with 95% CIs for progression-free survival (PFS) and overall survival (OS). As the ide-cel cohort only included infused patients, additional analyses were performed to emulate a real-world intention-to-treat population given the potential immortal time bias (patients in the ide-cel cohort were required to survive between apheresis and infusion). Specifically, patients in the teclistamab cohort who died within the first 24 days (median turnaround time for ide-cel manufacturing in United States in 2024) were excluded and 2 scenarios were performed to re-align T0 based on this 24-day period (either shifting teclistamab T0 forward or ide-cel T0 backward). Lastly, sensitivity analyses assessed differences in restricted mean survival time (dRMST) at 12 and 24 months. Results: A total of 281 patients met the inclusion criteria (ide-cel, N=106; teclistamab, N=175), with median follow-up of 22.4 and 13.7 months, respectively. IPTW adjustment balanced all covariates between groups (effective sample size: ide-cel, n=68; teclistamab, n=135). Adjusted analyses showed improved PFS with ide-cel versus teclistamab (HR, 0.67; 95% CI, 0.47–0.97), with median PFS of 11.3 versus 6.5 months. OS was also improved with ide-cel (HR, 0.59; 95% CI, 0.35–0.98); median OS was not reached in either group due to insufficient follow-up. There was a consistent trend of HRs favoring ide-cel versus teclistamab for both PFS and OS in both scenario analyses addressing the potential immortal time bias. Further, sensitivity analyses using dRMST confirmed statistically significant improvements in both PFS and OS with ide-cel across all scenarios at all time points evaluated. Conclusions: In this RW analysis, ide-cel was associated with superior PFS and OS compared with teclistamab in patients with TCE RRMM. These findings support emerging RW evidence favoring BCMA-directed CAR T cell therapies over bispecific antibodies and may inform treatment sequencing decisions in this high-risk population.

Abstract E1910 evaluated the addition of blinatumomab to chemotherapy in adults with B-acute lymphoblastic leukemia (ALL). The addition of blinatumomab in patients (pts) with measurable residual disease (MRD) negative (neg) B-ALL significantly improved both relapse-free and overall survival (NEJM 2024; 391: 320-33)1. Given the increasing use of blinatumomab and the E1910 backbone chemotherapy regimen, we evaluated &gt; Grade 3 toxicities on this trial in further detail. We assessed toxicity among the MRD-neg pts by age, gender, body mass index (BMI), combined cytogenetic-molecular risk, and number of cycles of blinatumomab received. We also evaluated toxicities during induction since this trial used a modified chemotherapy backbone. Methods: The eligibility, combined cytogenetic-molecular risk, and treatment have been previously described.1 All toxicities were &gt; Grade 3 by CTCAE version 4 with at least a possible relationship to treatment. Descriptive statistics were used to summarize the occurrence and rates of toxicities and Fisher's exact test was used to compare differences in proportions between groups. Analysis of induction included all pts who started treatment. Analysis of Step 3 toxicities included MRD-neg pts who started treatment on the blinatumomab (n=111) or chemotherapy only arm (n=112). Results: Pt characteristics: For induction (n=488), median age was 51 years (yrs) (range 30-70); 48.6% female. Combined cytogenetic-molecular risk: favorable (13.5%); intermediate (12.9%); no risk assigned (16.2%); unfavorable (57.4%). For induction, we compared toxicities for E1910 (n=488) to pts treated on a prior young adult study (n=289) (C10403) (Blood Adv 2021; 5(2): 504-12). The incidence of hyperglycemia (8% vs. 31.1%, p&lt; 0.001), aspartate aminotransferase (AST) increase (6.1% vs. 12.8%, p=0.002), alanine aminotransferase increase (ALT) (11.7% vs. 28.7%, p&lt; 0.001), and hyperbilirubinemia (11% vs. 19%, p=0.002) were significantly lower in E1910 pts. The incidence of pancreatitis (1.8%), thromboembolic events (4.5%), and febrile neutropenia (25.4%) in E1910 was similar to C10403. Toxicities in the MRD-neg pts in the blinatumomab arm (n=111): Despite a high incidence of neutropenia (74.8%) and thrombocytopenia (55.9%) in Step 3, there was a relatively low incidence of sepsis (7.2%), bacteremia (1.8%), cytokine release syndrome (CRS) (3.6%) and neurologic adverse events (0-6.3%). There was a higher incidence of neurological or psychiatric events in the blinatumomab arm (23%) versus chemotherapy arm (5%) (p &lt; 0.001) when all events were combined. There was a numerically higher incidence of ataxia (4.4% vs. %, p=0.16) and dysphasia (11.1% vs. 3%, p=0.12) in pts &gt; 55 yrs and a higher incidence of neutropenia (80.3% vs. 66.7%, p=0.12) and thrombocytopenia (62.1% vs. 46.7%, p=0.12) in the younger pts (age &lt; 55 yrs). In pts with a BMI &lt; 30 kg/m2 (vs. &gt; 30 kg/m2), there was a significantly higher incidence of leukopenia (51.7% vs. 26.4%, p=0.007) and thrombocytopenia (65.5% vs. 45.3%, p=0.037). However, this did not translate into an increased incidence of bleeding or infectious complications. By gender, females had a higher numerical incidence of AST increase (8.8% vs. 0%, p=0.057) and CRS (7% vs. 0% p=0.12); whereas males had a higher incidence of catheter- related infections (7.4% vs. 0%, p=0.05) and hyperglycemia (11.1% vs. 3.5%, p=0.16). A little more than half (56.8%) of pts received 4 cycles of blinatumomab with the remainder of pts receiving 1 (10.8%), 2 (28.8%), or 3 cycles (3.6%). Pts receiving 3-4 cycles of blinatumomab vs. 1-2 cycles of blinatumomab had a statistically higher incidence of anemia (38.8% vs. 6.8%, p&lt; 0.001), neutropenia (98.5% vs. 38.6%, p&lt; 0.001), and thrombocytopenia (83.6% vs. 13.6%, p&lt; 0.001), likely related to being on treatment for a longer period of time. Conclusions: Blinatumomab was well tolerated with no significant toxicity differences noted by age, gender, or number of cycles of blinatumomab received. Pts with a lower BMI did have an increased incidence of leukopenia and thrombocytopenia, possibly related to flat dosing of the drug. However, this did not translate into increased complications. Toxicites during induction were notably few, which suggests that this backbone with age adjustments may serve as a good backbone for future trials. Blinatumomab is being evaluated with low dose chemotherapy and other targeted agents in ongoing trials.