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Abstract Background Elranatamab is a B-cell maturation antigen (BCMA)-CD3–directed bispecific antibody approved in Japan for the treatment of patients with relapsed/refractory multiple myeloma (RRMM). To characterize the real-world (RW) use of elranatamab in Japan, we aimed to describe its dosing and treatment patterns in clinical practice. Methods EVEREST is a retrospective cohort study using de-identified hospital claims data from the Japan Medical Data Vision (MDV) database, which includes more than 40 million patients. Adult (age ≥18 years) patients with MM and ≥1 claim for elranatamab between March 26, 2024 (approval date), and March 31, 2025, were included. Patients who received elranatamab as part of a clinical trial were excluded. The index date was defined as the date of the first elranatamab claim. Treatment patterns were described across 3 time periods reflecting dosing and administration expectations per label: step-up dosing (SUD; index date to day 8), weekly (QW) maintenance period 1 (MP1, days 9-168), and every-2-week (Q2W) maintenance period 2 (MP2, day 169 onward). Descriptive statistics were used to summarize patient characteristics and treatment patterns. Estimated annual vial use was extrapolated from the reported mean time between doses throughout the follow-up period. Results A total of 253 patients were included in this analysis. The median age at index was 74 years (IQR, 69-79 years), 54.5% were female, 42.3% were penta-drug exposed, and 64.9% were treated at public hospitals. The median time from MM diagnosis to the index date was 60.4 months (IQR, 31.5-96.9). The median duration of elranatamab therapy from index date to last recorded administration was 60.0 days (IQR, 26-136 days). During the SUD period, 253 patients contributed 606 claims, of which 78.2% were 44 mg/1.1 mL vials, and most administrations (99.0%) occurred in the inpatient setting. The mean time between administrations was 4.0 days, with a median of 4.0 days (IQR, 3-4 days). In MP1, 226 patients contributed 1833 claims, of which 97.6% were 76 mg/1.9 mL vials, and 73.8% were administered in the outpatient setting. The mean time between administrations was 9.8 days, with a median of 7.0 days (IQR, 7-9 days). In MP2, 40 patients contributed 140 claims, of which 94.3% were 76 mg/1.9 mL vials, and 90.7% were administered in the outpatient setting. The mean time between administrations was 13.0 days, with a median of 14.0 days (IQR, 7-14 days). The projected annualized vial usage in the first year of treatment, based on the expected vial usage during SUD (3 doses) and the mean days between administrations in MP1 and MP2, was 34.4 vials. ConclusionsFindings from these early RW data provide insight into the initial adoption of elranatamab in Japan following its approval. Most patients followed the SUD schedule per label, with outpatient administration being common during maintenance periods. Dosing intervals generally aligned with label expectations, although the projected vial usage of elranatamab in this RW setting in Japan was lower than the expected usage per label. Additional studies with longer follow-up are needed to better understand the evolving treatment patterns.