Background: Multiple myeloma (MM) remains incurable, though key advances such as chimeric antigen receptor T-cells (CAR-T) and immunomodulatory agents, now evolving toward cereblon E3 ligase modulatory drugs (CELMoDs), have substantially improved the longevity and quality of life for patients (pts). Idecabtagene vicleucel (ide-cel) is a CAR-T targeting B-cell maturation antigen (BCMA), now US FDA-approved for pts who have received ≥2 prior lines of therapy including a proteasome inhibitor, immunomodulatory agent, and CD38 monoclonal antibody. Ide-cel was initially FDA-approved for ≥4 prior lines of therapy based on the KarMMa-1 study, which demonstrated a median progression-free survival (PFS) of 8.8 months across all cell doses and median overall survival (OS) of 19.4 months (Munshi et al., New Eng J Med 2021). Although promising, the fact that virtually all pts relapse post-ide-cel indicates that further progress is needed. To that end, iberdomide is an investigational CELMoD that in combination with dexamethasone has demonstrated a 30% response rate in early phase studies of triple class-refractory MM (Lonial et al., Lancet Haem 2022). Additionally, in laboratory-based correlative studies, iberdomide, at doses of ≤1 mg (well below the recommended phase 2 dose of 1.6 mg) was shown to augment immune function, including enhanced T-cell activation and cytotoxicity, and modulation of the cytokine milieu (Amatangelo et al., Cell Rep Med 2024). Iberdomide's combined properties of direct MM cytotoxicity and T-cell potentiation have clear, potential relevance to CAR-T clinically, providing the conceptual basis for the CADMIUM study (NCT06179888), exploring the effects of iberdomide as post-ide-cel maintenance therapy in MM.

Study Design and Methods: This is a randomized phase II trial with a safety run-in to evaluate if treatment with iberdomide maintenance post-ide-cel can significantly improve PFS vs. standard of care (SOC) observation without therapy, in pts with relapsed/refractory MM with ≥4 prior lines of therapy, who have received ide-cel within 3 months of registration, and no evidence of MM progression or additional MM therapy since ide-cel. Pre-ide-cel iberdomide exposure is permissible but refractoriness is not.

The safety run-in will confirm tolerability of the iberdomide dose to be carried forward, where doses to be tested include: iberdomide 1 mg orally on days 1-21 of a 28-day cycle (dose level 1; DL1) and iberdomide 0.7 mg on days 1-21 of a 28-day cycle (DL2). Dose-limiting toxicities (DLTs) include any of the following during the DLT period of a pt's first three months on iberdomide: prolonged Grade 3 non-hematologic toxicities, Grade 4 non-hematologic toxicities, prolonged Grade 4 neutropenia or thrombocytopenia, or any adverse event requiring iberdomide interruption for >4 weeks. Six pts will be enrolled onto DL1; if at most 1 of these pts has a DLT, DL1 will be carried forward to the randomized part of the study. Otherwise, 6 pts will be enrolled onto DL2. The randomized part of the trial will randomize 60 pts 1:1 to either iberdomide or SOC observation without therapy. A 1-sided log-rank test with α=0.15 has 81% power to detect a true hazard ratio (iberdomide/SOC) of 0.55 or less, corresponding to an improvement in median PFS to 16 vs. 8.8 months with SOC. One interim analysis for futility is planned. Secondary outcomes include OS, best response by International Myeloma Working Group (IMWG) criteria, and deepening of response, particularly conversion to complete response with a bone marrow minimal disease-negative state by Adaptive clonoSEQ (sensitivity 1e-6). Robust correlative studies will include CAR-T persistence, assays of T- and other immune cell function, and pathological analyses of whether BCMA expression on MM cells (prior to enrollment or at relapse) or other markers predict clinical outcomes.

Study status: To date, 12 pts have been screened, with 7 pts enrolled on study as part of the safety run-in (1 patient replaced). Enrollment data will be updated at presentation. Notably, an amendment is forthcoming which will enhance correlative studies and broaden eligibility criteria to include patients who have received ≥2 prior lines of therapy, conforming with ide-cel's current FDA label.

Study COI: BMS is supporting correlative studies.

Study Support: U10CA180821, U10CA180882; BMS; U10CA180868 (NRG Oncology); http://acknowledgements.alliancefound.org

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2025
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