Background: Patients with multiple myeloma (MM) remain at an increased risk of infection due to the disease process, as well as the ensuing treatments. Methods: We performed a systematic review to evaluate the monthly risk of grade III/IV infection, pneumonia, and neutropenia in patients with myeloma enrolled in randomized clinical trials (RCTs). Results: The risk of grade III or higher infection, pneumonia, and neutropenia persists among all phases of treatment. There was no statistical difference in grade III or higher infection, pneumonia, and neutropenia between frontline and relapsed/refractory setting. In the maintenance setting, the complications of infection, pneumonia, and neutropenia were low, but not negligible. Three-drug regimens were no more likely than two-drug regimens to have an increased risk of Grade III or higher infection. Conclusions: This is the first study to quantify the monthly risk of grade III or higher infection, pneumonia, and neutropenia across different treatment regimens in the frontline, maintenance, and relapsed/refractory settings. The results of our systematic review demonstrate a significant risk for severe infection, pneumonia, and neutropenia in patients with MM. Further studies are needed to determine the value of antibiotic prophylaxis in a broader myeloma patient population, as well as other approaches that will further mitigate the morbidity and mortality related to infection in this vulnerable patient population.

Chimeric antigen receptor (CAR) T-cell therapy has revolutionized treatment outcomes for patients with relapsed refractory multiple myeloma (RRMM). Despite supportive care with growth factors and thrombopoietin (TPO) mimetics, nearly half of the patients experience severe and prolonged cytopenias post CAR T infusion which have become a major therapeutic challenge for patients with RRMM. Given the successful use of CD34+ autologous hematopoietic stem cells for treatment of non- or delayed engraftment after allogeneic and autologous stem cell transplants, there is a need to explore the role of previously stored autologous stem cell as boosts for post CAR T cytpenias in RRMM. We performed a multicenter retrospective analysis of adult patients with RRMM who received previously collected and stored CD34+ stem cell boost post CAR T-cell therapy between 2 July 2020 and 18 January 2023. Indications for boost were determined per physician discretion and primarily included cytopenias and related complications. Overall, a total of 19 patients received stem cell boost, at a median dose of 2.75 × 106 CD34+ cells/kg (range 1.76-7.38), given at a median of 53 days (range 24-126) after CAR T infusion. Eighteen (95%) patients successfully recovered hematopoiesis after stem cell boost with median time for neutrophil, platelet, and hemoglobin engraftment of 14 (range 9-39), 17 (range 12-39), and 23 (range 6-34) days post boost, respectively. Stem cell boost were well tolerated with no patients experiencing infusion reactions. While infections were common and severe prior to stem cell boost, only one patient experienced a new infection after boost. All patients had experienced independence from use of growth factors, TPO agonists, and transfusions at the last follow up. Autologous stem cell boost can be effectively and safely used to promote hematopoietic recovery for post CAR T cytopenias in patients with RRMM. Stem cell boosts can be a veryeffective rescue measure for post CAR T cytopenias and related complications as well as supportive care needs.

Summary: Ide‐cel received approval for relapsed–refractory multiple myeloma based on the results of the KarMMa‐1 trial. However, patients with significant comorbidities, aggressive disease and prior B‐cell maturation antigen‐directed therapy (BCMA‐DT) were excluded. This retrospective study evaluated real‐world outcomes of patients who did not meet the KarMMa‐1 eligibility criteria and were treated with standard of care (SOC) ide‐cel. A total of 69 patients from three US centres who did not meet the KarMMa‐1 criteria underwent ide‐cel infusion. The main reasons for trial ineligibility included baseline grade 3–4 cytopenia (39%), prior BCMA‐DT (26%), renal impairment (19%) and Eastern Cooperative Oncology Group performance status ≥2 (14.5%). Cytokine‐release syndrome occurred in 81% vs. 84%, and immune effector cell‐associated neurotoxicity syndrome occurred in 28% vs. 18% of SOC versus KarMMa‐1 patients, respectively. Early infection (≤8 weeks post‐infusion) and severe infection rates were 42% vs. 49% and 30% vs. 22% for the SOC versus KarMMa‐1 cohorts, respectively. Grade 3–4 cytopenias for SOC versus KarMMa‐1 cohorts were: neutropenia (87% vs. 89%), anaemia (51% vs. 60%) and thrombocytopenia (65% vs. 52%). Overall response rate was higher for the SOC cohort (93% vs. 73%), as was the complete response or better rate (48% vs. 33%). However, median progression‐free survival and overall survival were comparable between the two groups. Our findings support broadening the inclusion criteria of future trials evaluating ide‐cel.

The use of 4-drug induction regimens for treatment naïve newly diagnosed multiple myeloma (NDMM) is associated with improved depth of response and progression-free survival (PFS). However, head-to-head trials of 4-drug combinations are lacking, and instead, these regimens are typically compared to 3-drug backbones; limiting the ability to discern whether any additional benefit (or toxicity) is simply additive or represents a synergy (or interaction). We conducted a meta-analysis of phase 2 and phase 3 clinical trials that randomized treatment naïve NDMM patients to either a 4-drug or 3-drug induction regimen. We included 11 trials which represented 6509 unique patients. PFS for all trials in the meta-analysis was 54 months with a 4-drug induction and 8.9 months with a 3-drug induction (HR: 0.49; 95% CI: 0.45; 0.54), but there was no benefit to using a 4-drug induction that did not include an anti-CD38 antibody (PFS 4-drug 8.1 months, PFS 3-drug 8.0 months; HR 0.95; 95% CI 0.86; 1.06). Adverse events were more frequent with the quadruplet regimens but were predominately mild. High-grade (≥3) adverse events (AEs) that were more common with 4-drug regimens were infections (RR: 1.34; 95% CI 1.17; 1.54) and thrombocytopenia (RR: 1.39; 95% CI 1.12; 1.74). This study suggests that 4-drug induction regimens which include an anti-CD38 antibody improve efficacy although with additional toxicity in NDMM patients.

Despite advances in treatment, outcomes remain poor for patients with penta-relapsed refractory multiple myeloma (RRMM). In this retrospective analysis, we evaluated the survival outcomes of penta-RRMM patients treated with (BCMA)- directed therapy (BDT). We identified 78 patients with penta-RRMM. Median age was 65 years, 29 (37%) had R-ISS stage III disease, 63 (81%) had high-risk cytogenetics, and 45 (58%) had extra-medullary disease. Median LOT prior to penta-refractory state was 5 (3–12). Amongst penta-RRMM, 43 (55%) were treated with BDT, 35 (45%) were not treated with BDT. Type of BDT received included belantamab mafadotin 15 (35%), Chimeric Antigen Receptor T-cell therapy 9 (21%), BCMA monoclonal antibody 6 (14%), and Bispecific T-cell engager 2 (5%). Eleven (25%) patients received more than one BDT. No significant differences were identified between baseline characteristics for the two groups. Patients treated with a BDT had better median overall survival, 17 vs. 6 months, HR 0.3 p-value < 0.001. Poor performance status, white race, and high-risk cytogenetics were associated with worse outcomes, whereas using a BDT was associated with better outcomes. Patients with penta-refractory MM have poor outcomes. Our retrospective analysis showed a significant survival benefit using BDT when compared to non-BDT for patients with penta-RRMM.