Spin, Paul

e19521 Background: Blindedindependent central review (BICR) committees are often established for oncology trials to assessbestoverall response (BOR), while real-world (RW) studies typically rely on physician-assessed responses. To emulate clinical trial rigor, a BICR committee was implemented in the R5458-ONC-21101 RW data-derived external control arm study (NCT05673967) to evaluate BOR using International Myeloma Working Group (IMWG) criteria. A pre-specified concordance analysis compared BOR assessments between the BICR committee and treating site physicians. Methods: RW data were obtained from chart reviews at 15 participating International Myeloma Foundation IMWG sites. The BICR committee, comprised of three multiple myeloma experts, evaluated BOR through consensus voting. Per protocol, the committee reviewed case report forms consisting of data on serum and urine myeloma protein and free light chain levels; and, where available, bone marrow plasma cell percentage, presence of plasmacytomas, and bone lesion changes. Concordance between BICR- and physician-assessed BOR was evaluated for objective response rate defined as ≥partial response (PR), ≥very good partial response (VGPR), ≥complete response (CR), and stringent complete response (sCR), with non-evaluable responses excluded from the analysis. Cohen’s kappa (κ) was used to measure agreement, with values >0.6 indicating strong concordance. 1 Results: Of 279 evaluable lines of therapy from 203 patients (Table), the BOR of ≥PR was 45.2% by BICR assessment and 42.3% by treating physicians (κ=0.622). Concordance improved for BOR of ≥VGPR (22.2% by BICR vs 24.7% by treating physicians; κ=0.731) but was low for BOR of ≥CR (3.9% vs. 10.8%; κ=0.508) and sCR (1.1% vs. 4.7%; κ=0.364). Conclusions: BICR- and physician-assessed responses showed strong concordance for BOR of ≥PR and ≥VGPR. However, as expected, lower concordance for ≥CR and sCR was observed, as evaluation of CR per IMWG criteria requires a bone marrow biopsy, which is rarely performed in clinical practice. While the reliability of CR and sCR in RW data is less certain, these results suggest that BOR of ≥VGPR or ≥PR may be reliably ascertained in academic settings based on treating physician evaluations. 1. Landis JR, Koch GG. Biometrics 1977;33(1):159–74. Clinical trial information: NCT05673967 . Agreement of BICR- and physician-assessed responses. BICR assessed Physician assessed Observed agreement, % Cohen’s kappa* Number of evaluable lines of therapy 279 279 - - ≥PR, n (%) 126 (45.2) 118 (42.3) 81.4 0.622 ≥VGPR, n (%) 62 (22.2) 69 (24.7) 90.3 0.731 ≥CR, n (%) 11 (3.9) 30 (10.8) 93.2 0.508 sCR, n (%) 3 (1.1) 13 (4.7) 96.4 0.364 *A kappa value >0.6 indicates strong concordance. 1

Introduction Linvoseltamab is an investigational, BCMA×CD3 bispecific antibody designed for the treatment of RRMM. High objective response rates (ORR) to linvoseltamab 200 mg in the LINKER-MM1 trial (NCT03761108) were demonstrated across high-risk subgroups, including patients aged ≥75 years, patients with high-risk cytogenetics, and patients with penta-class refractory status. The aim of this study was to compare ORR, overall and in key subgroups, between patients in Phase 2 of the LINKER-MM1 trial and patients in an international RW SOC external control arm (ECA). Methods The ECA was derived from a chart review of 16 academic sites across 10 countries that are part of the International Myeloma Foundation (IMF)-International Myeloma Working Group (IMWG) and 2 US electronic health record databases (COTA and Guardian Research Network [GRN]). Included patients initiated ≥1 anti-MM treatment after meeting key eligibility criteria of LINKER-MM1. Weighted random sampling and inverse probability of treatment weighting (IPTW) were used to select 1 line of therapy (LOT) per patient and balance the overall ECA and trial populations on prespecified prognostic factors (Kumar S, et al. IMS 2023). For ORR assessment, LINKER-MM1 and IMF-IMWG used independent central review committees per IMWG criteria, COTA used algorithmic assessment based on IMWG criteria, and GRN used physician-assessed responses. Prior to conducting comparative analyses, an independent committee of epidemiology and oncology experts reviewed the comparability of the cohorts and endpoint assessments, and approved study continuation. ORR among patients in LINKER-MM1 and patients in the ECA was compared overall and across prespecified subgroups (≥10 patients per subgroup), including age, race, cytogenetic risk score, international Staging System (ISS), presence of extramedullary plasmacytoma (EMP), refractory class, bone marrow plasma cell (BMPC) proportion, and number of prior LOTs. Results Median duration of follow-up was 14.3 months (data cut-off: January 6, 2024) for patients receiving linvoseltamab (n=105) and 13.6 months for the ECA (n=307; n=194, n=72, and n=41 from IMF-IMWG, COTA, and GRN, respectively). Following IPTW, 13 prognostic factors with <30% missingness were balanced between cohorts, with an effective sample size in the ECA of 197. After adjustment, ORR was significantly higher in patients who received linvoseltamab compared with patients in the ECA (69.5% vs 45.7%, odds ratio [OR] 2.5 [95% confidence interval (CI) 1.6-4.1]) and in key subgroups with age 65-74 years (76.9% vs 48.3%, OR 3.6 [1.6-8.6]), age ≥75 years (72.4% vs 48.5%, OR 2.8 [1.1-7.4]), Black or African American race (82.4% vs 25.0%, OR 14.0 [3.0-85.4]), White race (68.9% vs 49.7%, OR 2.2 [1.3-4.0]), standard cytogenetic risk (72.3% vs 51.3%, OR 2.5 [1.3-4.8]), ISS stage III (58.8% vs 19.7%, OR 5.8 [1.5-25.2]), absence of EMP (71.6% vs 49.3%, OR 2.6 [1.5-4.6]), triple-class refractory status (68.2% vs 45.7%, OR 2.6 [1.5-4.4]), quadruple-class refractory status (66.7% vs 45.9%, OR 2.4 [1.3-4.3]), 4-5 prior LOTs (65.1% vs 40.4%, OR 2.8 [1.3-6.0]), and >5 prior LOTs (75.7% vs 36.1%, OR 5.5 [2.4-13.6]). Numerically higher (not statistically significant) or similar ORR was observed for patients receiving linvoseltamab compared with patients in the ECA with age <65 years (59.5% vs 46.8%, OR 1.7 [0.79-3.6]), high-risk cytogenetics (65.0% vs 63.1%, OR 1.1 [0.41-2.9]), ISS stage I (73.3% vs 64.6%, OR 1.5 [0.62-3.7]), ISS stage II (67.6% vs 53.5%, OR 1.8 [0.72-4.7]), presence of EMP (58.8% vs 56.9%, OR 1.1 [0.32-3.8]), penta-class refractory status (64.3% vs 48.5%, OR 1.9 [0.78-4.8]), BMPC <50% (77.0% vs 67.2%, OR 1.6 [0.61-4.3]), BMPC ≥50% (41.7% vs 36.0%, OR 1.3 [0.36-4.7]), and ≤3 prior LOTs (68.0% vs 66.4%, OR 1.1 [0.43-2.9]). Separate findings will be presented for IMF-IMWG and COTA/GRN data at the congress. Conclusions Linvoseltamab induced better ORR vs RW SOC treatments overall, and better or similar ORR in the key subgroups assessed, highlighting its therapeutic value across a range of patients with RRMM with heterogeneous risk profiles and levels of disease burden.

7561 Background: Pts with TCE RRMM have poor outcomes and a high unmet need, with no established SOC tx. LINKER-MM1 (NCT03761108) is a single-arm, Phase 1/2 study investigating linvoseltamab, a B-cell maturation antigen × CD3 bispecific antibody, in pts with RRMM who were previously treated with a proteasome inhibitor, immunomodulatory drug, and anti-CD38 antibody, or were triple-class refractory (TCR) to these tx. The aim of this study was to contextualize LINKER-MM1 by comparing outcomes with linvoseltamab vs a real-world (RW) external control arm (ECA). Methods: A RW ECA was derived from 2 US electronic health record databases (COTA, Guardian Research Network) of pts who started a new line of therapy (LOT) after classification as TCE or TCR and met key eligibility criteria for LINKER-MM1. Eligibility was assessed at the initiation of each new LOT, and all eligible LOTs were included in the ECA. Data in Phase 2 pts who received linvoseltamab 200 mg in LINKER-MM1 were included (data cutoff: Sep 8, 2023). Inverse probability of tx weighting (IPTW) was used to reduce imbalances between the RW and LINKER-MM1 cohorts. Key prognostic factors were identified using a systematic review and rank ordered by an international committee of MM experts (Kumar et al., 2023). Outcomes included overall response rate (ORR), progression-free survival (PFS), time to next treatment (TTNT), and overall survival (OS). An independent committee of epidemiology and oncology experts reviewed the comparability of the cohorts and endpoint assessments prior to conducting comparative analyses. Results: Comparative analyses were performed in 105 pts in the linvoseltamab cohort and 101 RW pts (137 LOTs). Following IPTW, the distribution of cytogenetic risk, age, TCR status, Eastern Cooperative Oncology Group Performance Status, and platelet count were balanced between the 2 cohorts (absolute standardized mean difference <0.10). After adjustment, pts receiving linvoseltamab had significantly improved ORR, PFS, TTNT, and OS vs the RW ECA (see table). Conclusions: Linvoseltamab significantly improved outcomes vs RW SOC in the US, highlighting its potential as a highly effective tx in pts with TCE RRMM. [Table: see text]