Implementing the bispecific outpatient safe step-up (BOSS) program for elranatamab in ambulatory treatment of multiple myeloma.

Abstract

e19507 Background: Elranatamab, a BCMA-directed bispecific antibody, is highly effective in relapsed refractory multiple myeloma (RRMM). Inpatient monitoring for step-up dosing (SUD) is advised due to risk of cytokine release syndrome (CRS) and immune effector cell-associated neurotoxicity syndrome (ICANS), which can strain inpatient resources. To address this, we implemented the Bispecific Outpatient Safe Step-up (BOSS) program for outpatient administration. We report on its safety and feasibility compared to inpatient SUD (iSUD). Methods: Eligibility for the BOSS program was based on patient fitness, disease extent, LDH, ferritin, cytopenia, and proximity to MGH. Elranatamab SUDs were administered on Days 1 and 3, with a full dose on Day 8. Prophylactic dexamethasone (12 mg) was given on Days 2, 4-7, and 9, accompanied by remote daily safety calls by medical staff. Patients did not receive tocilizumab prophylactically. CRS management was escalated to inpatient as needed. Toxicity data were collected through the first full treatment dose and up to 14 days. Results: Of 43 patients who received elranatamab at MGH, 9 underwent outpatient SUD in the BOSS program. Median ages were 74 for BOSS and 73 for iSUD. BOSS had fewer median prior therapy lines (4 vs. 5), triple-class refractory disease (89% vs. 97%), and extramedullary disease (33% vs. 41%). CRS occurred in 33% of BOSS patients (all Gr 2), with a median onset of 2 days and duration of 31 hours. CRS occurred in 71% of iSUD patients (primarily Gr 1), with a median onset of 1 day and duration of 16 hours; no Gr 4 CRS was observed. Median hospital stay was 0 days (range 0-3) for BOSS and 5 days (range 3-17) for iSUD. Tocilizumab for CRS treatment occurred in 33% of BOSS patients vs 50% of iSUD. The rates of ICANS (11% vs. 27%), infections (11% vs. 29%), and hypogammaglobulinemia (22% vs. 32%) were all numerically lower in BOSS compared to iSUD. Conclusions: Our outpatient elranatamab SUD strategy is safe and feasible for RRMM patients through careful patient selection, dexamethasone alone for CRS prophylaxis, close toxicity monitoring, and prompt hospitalization. This approach reduces inpatient stays and alleviates healthcare resource burdens, enhancing patient experience. Baseline disease and characteristics of CRS: Elranatamab BOSS vs iSUD. n (%) BOSSCRS = YES3 (33%) BOSSTOTAL n=9 iSUD CRS = YES 24 (71%) iSUD TOTAL n=34 High-Risk Cytogenetics* 0 3 (33%) 15 (63%) 21 (62%) Baseline LDH elevated 0 1 (11%) 6 (25%) 7 (21%) Prior lines of therapy, median (range) 3 (3-7) 4 (3-9) 5 (3-10) 5 (3-12) Penta-drug exposure 1 (33%) 3 (33%) 11 (46%) 16 (47%) Prior CAR T 1 (33%) 6 (67%) 9 (38%) 16 (47%) Gr 2 or higher CRS 3 (100%) 3 (33%) 10 (42%) 10 (29%) > 1 CRS event 0 0 8 (33%) 8 (24%) Tocilizumab administered 3 (100%) 3 (33%) 17 (71%) 17 (50%) Median length of admission (range), days 3 (1-3) 0 (0-3) 6.5 (4-17) 5 (3-17) *17p13 deletion, t(4;14), t(14;16), t(14;20), gain or amplification 1q.