The EXCALIBER-RRMM result connects Zenbexus’ earlier MRD benefit with a significant improvement in progression-free survival.
Key Takeaways
- Zenbexus-based ZDd achieved a median progression-free survival of 42 months versus 20 months with DVd.
- The regimen reduced the risk of disease progression or death by 51%, meeting the second primary endpoint of EXCALIBER-RRMM.
- Zenbexus uses cereblon-mediated protein degradation to eliminate IKZF1 and IKZF3, weakening survival programs on which myeloma cells depend.
Data Snapshot
| Item | Details |
|---|---|
| Company | Bristol Myers Squibb |
| Product | Zenbexus |
| Generic name | Iberdomide |
| Trial | Phase 3 EXCALIBER-RRMM |
| Indication | Relapsed or refractory multiple myeloma |
| Experimental regimen | Zenbexus + daratumumab + dexamethasone (ZDd) |
| Comparator | Daratumumab + bortezomib + dexamethasone (DVd) |
| PFS analysis population | 800 patients |
| Median PFS | 42 months vs. 20 months |
| Hazard ratio | 0.49 |
| Risk reduction | 51% |
| Median follow-up | 23 months |
| FDA status | Accelerated approval granted in August 2026 |
PFS means progression-free survival, or the time patients remained alive without disease progression.
What Happened
On October 8, 2026, Bristol Myers Squibb reported positive topline results from the Phase 3 EXCALIBER-RRMM trial in patients with relapsed or refractory multiple myeloma.
Median progression-free survival reached 42 months with Zenbexus plus daratumumab and dexamethasone, compared with 20 months for daratumumab, bortezomib and dexamethasone. The hazard ratio was 0.49, representing a 51% reduction in the risk of disease progression or death. (Bristol Myers Squibb Phase 3 announcement)
Zenbexus had received FDA accelerated approval in August 2026 for adults who had received at least one prior line of therapy that included both a proteasome inhibitor and an immunomodulatory agent.
That approval was based on an earlier EXCALIBER-RRMM analysis showing a minimal residual disease-negative complete response rate of 41% with ZDd versus 21% with DVd. (FDA Zenbexus approval)
In EXCALIBER-RRMM, this earlier advantage in deep response was followed by a significant PFS benefit. Fierce Pharma noted that the new result fills out the efficacy profile that was incomplete when Zenbexus received accelerated approval. (Fierce Pharma analysis)
How Does Zenbexus Work?
Zenbexus contains iberdomide, an oral cereblon E3 ligase modulator, or CELMoD.
Iberdomide binds cereblon (CRBN), the substrate-recognition component of an E3 ubiquitin ligase complex. This interaction promotes the recruitment and ubiquitination of the transcription factors Ikaros (IKZF1) and Aiolos (IKZF3), marking them for destruction by the proteasome.
Degradation of IKZF1 and IKZF3 suppresses downstream transcriptional programs, including interferon regulatory factor 4 (IRF4)- and MYC-associated survival signaling. This contributes to anti-myeloma activity while also modifying immune-cell activity. (Peer-reviewed CELMoD mechanism review)
The mechanism can be summarized as:
Iberdomide → CRBN engagement → IKZF1/IKZF3 ubiquitination → proteasomal degradation → weaker myeloma survival signaling
This is not the restoration of a normal balance between IKZF1/3, IRF4 and MYC. Zenbexus deliberately degrades IKZF1 and IKZF3 to disrupt a transcriptional dependency of malignant plasma cells.
Daratumumab adds a complementary mechanism by targeting CD38 on myeloma cells. Preclinical studies found that iberdomide enhanced daratumumab-mediated antibody-dependent cellular cytotoxicity and complement-dependent cytotoxicity. Dexamethasone contributes additional anti-myeloma activity. (Zenbexus prescribing information)
Efficacy Came With a Clear Safety Trade-Off
In the previously reported EXCALIBER-RRMM safety analysis, Grade 3 or 4 neutropenia occurred in 84.3% of patients receiving ZDd, compared with 11.3% receiving DVd. Grade 3 or 4 infections occurred in 39.2% and 21.6%, respectively.
Conversely, any-grade peripheral sensory neuropathy occurred in 12.3% of the ZDd group versus 42.6% of the bortezomib-containing DVd group.
ZDd therefore delivered deeper and longer disease control with less peripheral neuropathy, but substantially more severe neutropenia and infection risk. (Detailed EXCALIBER-RRMM results)
Selected Competing and Adjacent Multiple Myeloma Therapies
| Company | Therapy | Status and eligible setting | Clinical and practical profile |
|---|---|---|---|
| Bristol Myers Squibb | Zenbexus + Darzalex + dexamethasone | FDA accelerated approval after at least one prior line including a proteasome inhibitor and an immunomodulatory agent | Oral Zenbexus on Days 1–21 of each 28-day cycle; strong PFS result but substantial neutropenia and infection risk |
| Johnson & Johnson | Tecvayli + Darzalex | FDA approved after at least one prior line including a proteasome inhibitor and an immunomodulatory agent | BCMA×CD3 T-cell redirection plus CD38 targeting; subcutaneous treatment with step-up dosing and CRS, neurologic and infection risks |
| Johnson & Johnson / Legend Biotech | Carvykti | FDA approved after at least one prior line including a proteasome inhibitor and an immunomodulatory agent in lenalidomide-refractory disease | One-time autologous BCMA CAR-T infusion; treatment-free potential after infusion but patient-specific manufacturing and intensive safety monitoring |
| AbbVie | Etentamig | Investigational; positive Phase 3 CERVINO results in triple-class-exposed disease | BCMA×CD3 bispecific antibody; monthly intravenous dosing after one step-up dose |
| Bristol Myers Squibb | Mezigdomide + carfilzomib + dexamethasone | FDA application under review; target decision date May 13, 2027 | Oral next-generation CELMoD combined with an intravenous proteasome inhibitor; an adjacent BMS asset rather than an external competitor |
These therapies were evaluated in different patient populations and trials, so their efficacy results should not be compared directly.
Tecvayli plus Darzalex is the most relevant approved immune-based alternative in the same broad post-first-line setting. (FDA Tecvayli plus Darzalex approval)
Carvykti offers a different treatment model based on a single autologous CAR-T infusion, but eligibility, manufacturing time and treatment logistics limit direct comparison with an oral drug-based regimen. (FDA Carvykti information)
Etentamig reduced the risk of progression or death by 60% in the Phase 3 CERVINO trial, but it was evaluated in a more heavily pretreated, triple-class-exposed population. (AbbVie CERVINO results)
Why It Matters
The result provides clinical support for incorporating cereblon-mediated protein degradation into a daratumumab-based myeloma regimen.
It also strengthens the evidence behind Zenbexus’ accelerated approval. However, the PFS result does not automatically convert the indication to traditional approval. Bristol Myers Squibb must submit the confirmatory evidence, and the FDA will determine whether it verifies clinical benefit.
The current announcement remains a topline disclosure. Confidence intervals for the PFS analysis, detailed subgroup results and mature overall survival data have not been released. Full results are expected at the American Society of Hematology annual meeting.
BP View
Zenbexus has now moved beyond an approval supported only by a surrogate endpoint. The 42-month median PFS result shows that the ZDd regimen produced substantially longer disease control than DVd in EXCALIBER-RRMM.
Its practical advantage is an oral protein degrader that can be incorporated into a daratumumab-based regimen without the individualized manufacturing required for CAR-T therapy. Its principal limitation is the high burden of neutropenia and infection.
The competitive question is no longer whether Zenbexus works. It is whether its balance of durability, safety and treatment convenience can compete with earlier-line BCMA bispecific antibodies and CAR-T therapy.
What do you think will matter more in relapsed multiple myeloma: longer disease control, lower treatment burden or a more manageable safety profile? Share your view in the comments.
Related Post
For the regulatory story that preceded this confirmatory result, read my previous analysis:
Bristol Myers Squibb Wins FDA Approval for the First CELMoD Therapy in Multiple Myeloma
About BP
Biopharma Perspective explains global biopharma news through clinical evidence, molecular mechanisms and competitive strategy.
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