As of June 2, 2021, 107 pts had received IBER + DEX. Median age was 64 (44–83) years; median time since initial diagnosis was 6.9 (1.6–24.5) years. Extramedullary plasmacytomas were present in 25.2% of pts; 29.9% of pts had high-risk cytogenetics. Median number of prior regimens was 6 (3–23). All pts were triple-class exposed; prior therapies included autologous stem cell transplantation (78.5%), PIs (100%), IMiD agents (LEN [100%] and POM [100%]), and anti-CD38 mAbs (100%); 99.1% of pts were refractory to last myeloma regimen and 97.2% of pts were triple-class refractory. Median follow-up was 7.69 (0.5–17.5) months, with a median number of 4 (1–17) cycles received and 13 (12.1%) pts continuing treatment. Main reason for discontinuation was progressive disease (69.2%).

ORR was 26.2%, with 1 (0.9%) stringent complete response, 8 (7.5%) very good partial responses, and 19 (17.8%) partial responses (Table); the clinical benefit rate (≥ minimal response) was 36.4% and disease control rate (≥ stable disease) was 79.4%. Median duration of response was 7.0 (4.5–11.3) months (Table), median progression-free survival was 3.0 (2.8–3.7) months, and median overall survival was 11.2 (9.0–not reached) months. Similar response rates were observed among a cohort of pts also exposed to BCMA therapies (N = 24, Table).

Grade (Gr) 3–4 treatment-emergent adverse events (TEAEs) were reported in 88 (82.2%) pts. Most frequent (≥ 20% pts) hematologic Gr 3–4 TEAEs were neutropenia (44.9%; and 4.7% febrile neutropenia), anemia (28.0%), thrombocytopenia (21.5%), and leukopenia (20.6%). Gr 3–4 infections were reported in 27.1% of pts; Gr 3–4 pneumonia and COVID-19 occurred in 10.3% and 4.7% of pts, respectively. Occurrence of other Gr 3–4 non-hematologic TEAEs was generally low, including gastrointestinal disorders (5.6%), fatigue (2.8%), rash (1.9%). Fifty-six (52.3%) pts and 20 (18.7%) had IBER dose interruptions and reductions due to TEAEs, respectively. Five (4.7%) pts discontinued due to TEAEs. No pt discontinued IBER due to neutropenia.