The Mezi dose selected for stage 2 was 1.0 mg. In total, 479 pts (288 MeziKd at 1.0 mg Mezi; 191 Kd) were included in the analysis. Median (range) age was 68 (30–85) y with 25.1% of pts ≥75 y; median (range) number of prior LOTs was 2 (1–9); 92.1% of pts were triple-class-exposed, with 85.8% refractory to an anti-CD38 mAb and 75.8% to LEN; 37.2% were exposed to pomalidomide and 7.3% to anti-BCMA tx. At data cutoff, median follow-up was 10.6 mo with 52.4% (MeziKd) and 31.4% (Kd) of pts still on tx. Median tx duration was 8.9 (up to 32.1) mo for MeziKd vs 6.2 (up to 25.0) for Kd. 

MeziKd significantly improved PFS vs Kd (median [95% CI], 18.0 [14.5–22.1] vs 8.3 [5.6–10.7] mo; HR, 0.48 [95% CI, 0.36–0.63]; P<0.0001), which was consistent across subgroups, including pts with >2 prior LOTs, prior tx exposure/refractoriness, high-risk cytogenetics, extramedullary disease, and age ≥75 y. Higher ORR (80.2% vs 53.4%) and complete response or better (26.7% vs 8.9%) were seen with MeziKd. Deaths were reported in 21.5% (MeziKd) vs 26.7% (Kd) of pts, mostly due to progressive disease. Grade (Gr) 3–4 treatment-emergent adverse events were seen in 83.7% vs 56.5% of pts, neutropenia in 61.1% vs 9.1%, and infections in 34.0% vs 15.6% with MeziKd and Kd, respectively; Gr 5 infections in this high-risk population were few (2.4 vs 1.1%).