ASCO: BMS's CELMoD mezigdomide reduces progression risk by 52% in Phase III multiple myeloma trial

Bristol Myers Squibb (NYSE: BMY) reported that mezigdomide, its oral cereblon E3 ligase modulator (CELMoD), cut the risk of disease progression or death by 52% versus carfilzomib and dexamethasone alone in relapsed or refractory multiple myeloma, delivering the first Phase III readout for any CELMoD agent and handing BMS a potential new commercial pillar as its immunomodulatory drug franchise faces generic erosion from lenalidomide biosimilars. The data were the subject of a late-breaking oral presentation at the 2026 American Society of Clinical Oncology (ASCO) summit meeting.

The SUCCESSOR-2 trial is a seamless Phase II/III, multicenter, randomized, open-label study that enrolled 479 patients with relapsed or refractory multiple myeloma, randomized to mezigdomide plus carfilzomib and dexamethasone (MeziKd, n=288) or carfilzomib and dexamethasone alone (Kd, n=191). The population was heavily pretreated and largely refractory to current standards: 92.1% were triple-class-exposed, 85.8% were refractory to an anti-CD38 monoclonal antibody, and 75.8% were refractory to lenalidomide — the very drug class from which mezigdomide descends.

The primary endpoint was met decisively. Median progression-free survival reached 18 months with MeziKd versus 8.3 months with Kd (HR: 0.48; 95% CI reported; p < 0.0001), a hazard ratio that corresponds to a 52% reduction in the risk of progression or death at a median follow-up of 10.6 months. Overall response rate was 80.2% with MeziKd versus 53.4% with Kd, and complete response or better was achieved in 26.7% versus 8.9%. Median overall survival had not yet been reached in either arm. The results were presented as a late-breaking oral at Bristol Myers Squibb ASCO 2026 (#LBA7506).

The safety profile carries a meaningful hematologic burden. Grade 3–4 treatment-emergent adverse events occurred in 83.7% of MeziKd patients versus 56.5% on Kd. Neutropenia was the dominant toxicity, appearing in 61.1% of the MeziKd arm versus 9.1% on Kd, and Grade 3–4 infections occurred in 34.0% versus 15.6%. BMS described the profile as consistent with mezigdomide's known safety profile, and notably 52.4% of MeziKd patients remained on treatment at data cutoff versus 31.4% on Kd, suggesting tolerability sufficient for continued dosing in a substantial proportion of patients.

Competitive context and outlook

The SUCCESSOR-2 trial results arrive at a moment when the relapsed refractory multiple myeloma treatment landscape is undergoing rapid reorganization. Bispecific T-cell engagers — including Janssen's Tecvayli (teclistamab), Janssen's Talvey (talquetamab), and Pfizer's Elrexfio (elranatamab) — have reshaped late-line practice since 2023, while the CAR-T therapies Janssen and Legend Biotech's Carvykti (ciltacabtagene autoleucel) and BMS's own Abecma (idecabtagene vicleucel) have moved into earlier relapse settings following label expansions in 2024. Against this backdrop, mezigdomide's oral administration, outpatient delivery, and activity in a predominantly anti-CD38-refractory and lenalidomide-refractory population position it as a chemotherapy-free oral option that does not require the manufacturing lead times of CAR-T or the step-up hospitalization protocols associated with bispecifics.

CELMoD therapy in RRMM builds on the mechanistic foundation established by lenalidomide and pomalidomide but with substantially greater potency. Mezigdomide is optimized for maximal and rapid degradation of Ikaros and Aiolos transcription factors, proteins essential for myeloma cell survival, and preclinical data suggest it also reinvigorates exhausted T cells — a property that may become clinically relevant as the field increasingly uses it alongside immunotherapy backbones. The carfilzomib and dexamethasone combination was a deliberate design choice: Kd is an established standard of care in second- and third-line RRMM, making it a credible comparator and the PFS improvement over it directly interpretable for practicing oncologists.

Cross-trial comparisons are limited by differences in patient populations, prior therapy exposure, and follow-up duration, but the 18-month median PFS in a population that was more than 85% anti-CD38-refractory compares favorably to historical benchmarks for pomalidomide-based triplets in similar settings. The ORR of 80.2% and the complete response rate of 26.7% are also notable in a population where most patients had already received two or more prior lines including an IMiD and an anti-CD38 antibody.

BMS has indicated it will share the SUCCESSOR-2 data with health authorities, and a regulatory submission appears imminent. A second ongoing Phase III trial, SUCCESSOR-1, is evaluating mezigdomide in a separate RRMM combination, broadening the potential label scope. The company has framed mezigdomide as the centerpiece of its next-generation targeted protein degradation platform, which also encompasses ligand-directed degraders and degrader antibody conjugates — modalities that have not yet generated pivotal data but represent BMS's long-term bet on cereblon biology beyond the IMiD era.

For BMS, the commercial stakes are substantial. Revlimid (lenalidomide) generic entry has been eroding one of the company's most durable revenue streams, and pomalidomide faces its own competitive pressure from bispecifics in later lines. Mezigdomide, if approved, would enter a market where oral convenience, outpatient administration, and activity in anti-CD38-refractory disease are genuine differentiators — though the neutropenia rate will require careful management and may limit use in older or frailer patients without growth factor support. The next milestone is a regulatory filing, with the timeline to be confirmed following health authority discussions.

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