P-014: Efficacy and Safety of ABBV-383, a BCMA Bispecific Antibody, in Black Patients With Relapsed/Refractory Multiple Myeloma: A Subgroup Analysis of a Phase 1 Trial

Introduction: There is an unmet need for novel therapies with convenient dosing and improved safety to optimize patient (pt) adherence and outcomes in multiple myeloma (MM), particularly for disease refractory to current therapies. ABBV-383, a distinctive, next-generation B-cell maturation antigen × CD3 T-cell–engaging bispecific antibody, has demonstrated promising results in an ongoing first-in-human phase 1 trial in relapsed/refractory MM (RRMM) pts (Rodriguez et al. ASCO 2024. Abstract 7531; Weisel et al. EHA 2024. Abstract S211). Although MM incidence is higher in some historically underrepresented populations, there remains limited clinical outcomes data for these pt groups. Here we report the efficacy and safety of ABBV-383 at 40–60 mg in the Black/African American subgroup from this ongoing phase 1 trial (NCT03933735).

Methods: This phase 1 open-label, dose-escalation/expansion trial enrolled pts with RRMM who received ≥3 prior lines including a proteasome inhibitor, an immunomodulatory drug, and an anti-CD38 monoclonal antibody. In the dose-expansion phase, ABBV-383 was evaluated at 40 or 60 mg Q3W and 60 mg Q4W. Demographics and efficacy, safety, and pharmacokinetics (PK) of ABBV-383 were analyzed in Black/African American pts in this trial.

Results: In total, 37/220 (17%) pts were Black/African American with 17% (24/140) in 40- to 60-mg dose cohorts. Median age was 62 years, with 4 median lines of prior therapy (range 3–10). As of January 18, 2024, median duration of follow-up was 21.5 months. Objective response rate was 61% (14/23 pts), with 57% (13/23) of pts having ≥VGPR and 39% (9/23 pts) with ≥CR. Median progression-free survival was 11.8 months (4.7, NE). Treatment-emergent adverse events of any grade (G)/G3/4 occurred in all (100%)/18 (75%) pts, respectively. Incidence of G3/4 neutropenia was 33% (8 pts), anemia 25% (6 pts), and thrombocytopenia 13% (3 pts). G3/4 infections rate was 21% (5 pts); the most common infections were COVID-19 (2 pts; 8%) and pneumonia (2 pts; 8%). There was no reported ICANS in this subgroup and CRS occurred in 15 pts (63%); 12 pts (50%) had G1 and 3 pts (13%) had G3 CRS. The ABBV-383 population PK analysis using data from the phase 1 trial (Polepally et al. ASCPT 2024. Abstract PII-065) indicated that race (Black/African American vs White/Other) was a nonsignificant covariate.

Conclusions: ABBV-383 demonstrated a tolerable safety profile and antitumor activity in Black/African American pts that was comparable with the total pt population (Rodriguez et al. ASCO 2024. Abstract 7531; Weisel et al. EHA 2024. Abstract S211). In addition, clinical outcomes between racial groups were similar when the equivalent treatment was administered. Furthermore, no difference in PK was found between Black/African American and White/Other pts. No new safety signals were reported. ABBV-383 at 60 mg Q4W will be investigated in the registrational phase 3 trial (NCT06158841) in RRMM.