SUMMARY: Multiple Myeloma (MM) is a clonal disorder of plasma cells in the bone marrow and the American Cancer Society estimates that in the United States, 36,000 new cases will be diagnosed in 2026, and 10,850 patients are expected to die of the disease. Multiple Myeloma is a disease of the elderly, with a median age at diagnosis of 69 years and characterized by intrinsic clonal heterogeneity. Almost all patients eventually will relapse, and patients with a high-risk cytogenetic profile, extramedullary disease or refractory disease have the worst outcomes.
Modern therapies,including Proteasome Inhibitors, Immunomodulatory drugs, and anti-CD38 antibodies, have extended survival to nearly a decade. However, patients whose disease becomes resistant to these treatments face poor outcomes with a median survival of less than 1 year. There is a critical need for novel, effective therapies with new mechanisms of action.
Targeted Protein Degradation
Cereblon is a key human protein encoded by the CRBN gene that acts as a primary target for immunomodulatory drugs (IMiDs) like Lenalidomide, Pomalidomide, and Thalidomide. It functions as a receptor that labels specific proteins for cellular destruction, driving tumor cell death and activating the immune system.
CELMoDs (Cereblon E3 Ligase Modulators) are a new class of highly potent oral medications designed primarily to treat multiple myeloma. They work as targeted “molecular glue” by binding to the cereblon protein, similar to immunomodulatory drugs. However, they bind with much higher affinity and induce a more active, “closed” conformation. This enhanced biochemical grip allows them to be effective even in patients whose disease has become resistant to standard IMiDs. Once cereblon is activated by the CELMoD, it acts as a garbage disposal signal (ubiquitin) to mark specific target proteins, most notably Ikaros (IKZF1) and Aiolos (IKZF3), for destruction by the cell’s proteasome.
Ikaros (IKZF1) and Aiolos (IKZF3) are zinc-finger transcription factors that regulate lymphocyte development. These transcription factors in many hematological malignancies such as multiple myeloma and leukemia act as rogue cancer-driving proteins, supporting cancer cell survival by repressing tumor suppressors and driving oncogene expression, and are heavily relied upon by myeloma cells to survive and multiply.
When CELMoDs destroy these proteins, it arrests the cancer cell’s growth cycle and actively triggers apoptosis (programmed cell death). Further, Destroying Ikaros and Aiolos removes the natural brakes that suppress immune function, allowing T cells and Natural Killer (NK) cells to better attack the tumor.
Prominent CELMoDs under study include Iberdomide and Mezigdomide, and are being investigated both as standalone therapies and in combination with other treatments like monoclonal antibodies for patients who have Relapsed/Refractory Multiple Myeloma (RRMM).
Mezigdomide, an investigational oral cereblon E3 ligase modulator (CELMoD), has been specifically engineered to promote rapid and potent degradation of the transcription factors Ikaros and Aiolos. Compared with earlier immunomodulatory agents, Mezigdomide demonstrates enhanced anti-myeloma activity and greater immune stimulation in preclinical studies, including restoration of T-cell function and reversal of immune exhaustion. The Phase 3 SUCCESSOR-2 trial evaluated whether adding Mezigdomide to Carfilzomib and Dexamethasone could improve outcomes in this difficult-to-treat patient population.
SUCCESSOR-2 Study Design
SUCCESSOR-2 (NCT05552976) is a global, randomized, open-label, Phase 3 trial enrolling adults with RRMM who had received at least one prior line of therapy, including both Lenalidomide and an anti-CD38 monoclonal antibody. The study used a seamless two-stage design, with the initial stage identifying the optimal Mezigdomide dose before proceeding to the confirmatory efficacy comparison.
Patients received Mezigdomide combined with weekly Carfilzomib and Dexamethasone (MeziKd), or Carfilzomib plus Dexamethasone (Kd). Following dose optimization, the 1.0-mg Mezigdomide dose was selected for the second stage of the study. The Primary endpoint was Progression-Free Survival (PFS), while Secondary endpoints included Overall Survival (OS), Overall Response Rate (ORR), Duration of Response, Minimal Residual Disease negativity, time to next treatment, and patient-reported Quality of Life.
Clinically Meaningful Improvement in Disease Control
The efficacy analysis included 479 patients, with 288 receiving MeziKd and 191 receiving Kd alone. Participants represented a heavily pretreated population with substantial treatment resistance. More than 92% had prior exposure to all three major therapeutic classes, nearly 86% were refractory to anti-CD38 therapy, and approximately 76% were refractory to Lenalidomide. Over one-third had previously received Pomalidomide, and a smaller proportion had been exposed to anti-BCMA therapy.
After a median follow-up of 10.6 months, MeziKd significantly prolonged PFS compared with Kd alone. Median PFS reached 18.0 months with the Mezigdomide regimen versus 8.3 months for the control arm, corresponding to a 52% reduction in the risk of disease progression or death (HR=0.48; P<0.0001). Importantly, the benefit was consistently observed across clinically relevant subgroups, including patients treated at first relapse, those with more than two prior lines of therapy, individuals with high-risk cytogenetic abnormalities, patients with extramedullary disease, and those aged 75 years or older.
Treatment responses also favored the investigational regimen. The ORR increased to 80.2% with MeziKd compared with 53.4% for Kd alone, while Complete Responses or better were achieved in 26.7% and 8.9% of patients, respectively. Patients receiving MeziKd also remained on therapy longer than those receiving the standard regimen.
Safety Profile Remains Predictable
The safety findings were consistent with previous clinical experience using Mezigdomide and with the known toxicities of the individual treatment components. Grade 3 or 4 treatment-emergent adverse events occurred more frequently with MeziKd than with Kd alone, largely reflecting higher rates of neutropenia and infections. Grade 3-4 neutropenia was observed in 61.1% of patients receiving MeziKd compared with 9.1% in the control arm, while Grade 3-4 infections occurred in 34.0% and 15.6% of patients, respectively. Despite these differences, fatal infections remained uncommon in both treatment groups, and adverse events were generally considered manageable with appropriate supportive care and monitoring.
Clinical Perspective
SUCCESSOR-2 provides compelling evidence that Mezigdomide combined with Carfilzomib and Dexamethasone can substantially improve clinical outcomes in patients with RRMM previously exposed or refractory to Lenalidomide and anti-CD38 therapy. The nearly 10-month improvement in median PFS, together with higher response rates across multiple high-risk subgroups, highlights the potential of cereblon E3 ligase modulation as an important therapeutic strategy in contemporary myeloma management.
As treatment sequencing continues to evolve and more patients become refractory to frontline therapies, MeziKd has the potential to become an important option beginning at first relapse and may represent a future standard-of-care regimen pending regulatory review and longer-term survival follow-up.
Mezigdomide, carfilzomib, and dexamethasone (MeziKd) vs carfilzomib and dexamethasone (Kd) in relapsed/refractory multiple myeloma (RRMM): Results from the phase 3 SUCCESSOR-2 trial. Richardson PG, Schjesvold F, Fu C, et al. J Clin Oncol 44, LBA7506(2026)
