Real-world safety of elranatamab in low-weight patients: Findings from the SUMMIT study.

e23364 Background: Elranatamab is the first BCMA bispecific antibody approved in Japan for treatment of patients with heavily pre-treated multiple myeloma (MM). Although prior clinical work supports the safety of elranatamab’s fixed dose formulation (Elmeliegy 2025), assessing its tolerability across different patient weights in a real-world (RW) context is important, especially in typically lower weight Asian populations. This study aimed to characterize the safety of elranatamab among RW patients with MM by weight in Japan. Methods: SUMMIT is a retrospective cohort study using deidentified administrative claims data from the Japan Medical Data Vision database. Adult patients with a diagnosis of MM who first received elranatamab from March 26, 2024, to March 31, 2025 outside of clinical trials, were included in the study. Five subgroups were created using baseline weight quartiles and a ≤40kg very low-weight (VLW) group. Baseline characteristics and elranatamab administration patterns were reported descriptively. The incidence of adverse events including CRS (Cytokine Release Syndrome), ICANS (Immune Effector Cell-Associated Neurotoxicity Syndrome), and cytopenia (encompassing anemia, leukopenia, lymphopenia, neutropenia, pancytopenia, and thrombocytopenia), was estimated among at-risk patients who had no prior history of the respective events within the preceding 30 days using disease codes following elranatamab initiation (14 days [d], cytopenia only: 8d, 30d). Results: Results for n = 258 elranatamab patients are summarized in Table 1. Safety outcomes were similar across all weight groups, with CRS (14d) ranging 45.5-50.8%. Cytopenia (30d) was similar across quartiles (23.2-28.3%) but differed in the VLW group (43.8%). Conclusions: Safety outcomes and elranatamab administration patterns were comparable for Japanese patients by weight. Further investigation in larger samples of this population is warranted. Baseline characteristics, elranatamab administration and incidence of safety outcomes by weight for RW Japanese patients. VLW≤40.0 kgn=22 Q1≤48.0 kgn=66 Q2>48.0-54.6 kgn=63 Q3>54.6-62.0 kgn=66 Q4>62.0-96.1 kgn=63 Age (median[IQR]) 76.5(69.0-82.0) 74.0(70.0-80.0) 76.0(69.0-79.0) 74.5(68.0-78.0) 72.0(64.0-76.0) Female, n(%) 22 (100.0) 59 (89.4) 43 (68.3) 24 (36.4) 12 (19.0) Time to first full dose, d (median[IQR]) 9.0(7.0-14.0) 8.0(7.0-14.0) 10.0(7.0-13.0) 7.0(7.0-10.0) 7.0(7.0-8.0) CRS (14d), n(%*) 10 (45.5) 30 (45.5) 32 (50.8) 32 (49.2) 29 (46.0) ICANS (14d), n(%*) 0 (0.0) 0 (0.0) 4 (6.3) 3 (4.5) 2 (3.2) Cytopenia (8d), n(%*) 3 (16.7) 6 (10.5) 13 (22.8) 10 (16.7) 11 (19.3) Cytopenia (14d), n(%*) 4 (23.5) 8 (14.5) 14 (25.0) 12 (20.7) 11 (20.0) Cytopenia (30d), n(%*) 7 (43.8) 15 (28.3) 14 (25.9) 13 (23.2) 13 (24.5) *Percentages are calculated based on the at-risk population, not the total cohort.