This multicenter retrospective study is among the first to evaluate the efficacy and tolerability of conventional debulking chemotherapy prior to initiating anti-BCMA bispecific antibody therapy in patients with RRMM and either EMD or high tumor burden. Our findings suggest that this sequential approach is both effective and tolerable, even in a high-risk, heavily pretreated patient population.
Our cohort had a median of four prior treatment lines, and 93% of patients were triple-class refractory. Half had EMD and 50% had high-risk cytogenetics—both markers of poor prognosis. Despite these adverse features, the ORR after the first BsAb cycle was 64%, comparable to results from pivotal trials such as MajesTEC-1 and MagnetisMM-3, which reported ORRs of 63% and 61%, respectively [5–9]. Among patients with EMD, the ORR was 53% after both cycle one and three, increasing to 77.8% at six cycles. These results are particularly notable given prior data showing limited efficacy of BsAbs in EMD, such as the 0% ORR reported in a subgroup analysis of MagnetisMM-3 in patients with ISS stage III and EMD or high-risk cytogenetics [9].
Herein, the choice of chemotherapy was largely based on alkylating agents, especially cyclophosphamide (84%). Cyclophosphamide not only induces cytotoxicity but also modulates the immune microenvironment, reduces T-cell exhaustion, and enhances T-cell activation—all potentially boosting BsAb efficacy [19]. These immunomodulatory effects, combined with tumor debulking, may help improve the effector-to-target cell ratio, which plays a key role in the success of BsAb therapies. There is also a theoretical rationale that chemotherapy-induced cell death may promote neoantigen release and immune priming, further amplifying BsAb effectiveness [20, 21].
In 27% of patients, alkylating agents were combined with anthracyclines, and 50% received etoposide. These regimens resemble intensive protocols such as DT-PACE, previously used in EMD before the advent of immunotherapy. However, 68% of patients received only a single cycle of chemotherapy, which likely reduced cumulative toxicity while achieving rapid cytoreduction [12, 13].
At a median follow-up of 12 months in our study, median progression-free survival (PFS) was 10.2 months. Patients without EMD had a significantly longer PFS (16.1 vs. 11.9 months; p = 0.05). These outcomes align with prior BsAb trial data, such as teclistamab (11.3 months) and elranatamab (17.6 months) [5–9]. In the IFM 2024-09 real-world study, the median PFS for patients with EMD was 3.7 months vs 11.3 months for patients without EMD treated by Teclistamab [10]. A real-world analysis of teclistamab use in Germany show an ORR of 37.2% and a median PFS of 2.07 months for patients with EMD [11]. In contrast, our results suggest improved disease control in this subgroup, although long-term benefit remains limited. This highlights the need for continued efforts to optimize treatment for patients with EMD.
The safety profile of this approach was acceptable given the heavily pretreated patient population [24–26]. Despite prior chemotherapy, the incidence of cytokine release syndrome (CRS) and immune effector cell-associated neurotoxicity syndrome (ICANS) remained low—7% for ICANS and no apparent increase in CRS severity [24–27]. Hematological toxicity ≥ grade 3 occurred in 33% of patients, and infections ≥ grade 3 were reported in 35%. This observation suggests that prior chemotherapy does not significantly increase the risk or severity of CRS associated with bispecific antibodies, countering some theoretical concerns. Preventive strategies, including immunoglobulin supplementation, antibiotic and antiviral prophylaxis, and pneumocystis prevention, were widely used and likely contributed to infection management. Importantly, toxicity rates were similar between patients with and without EMD, suggesting that worse disease biology does not necessarily imply greater treatment-related toxicity.
The retrospective nature and modest size of our study introduce limitations. The heterogeneity of chemotherapy regimens and the lack of a comparator group make it difficult to draw definitive conclusions about the superiority of the sequential approach over BsAb monotherapy. Infrequent PET-CT assessments also limited our ability to fully evaluate depth of response, especially in patients with EMD.
Prospective trials are needed to refine these aspects and to validate our findings. Additionally, translational studies evaluating immune markers, T-cell subsets, and changes in the tumor microenvironment before and after chemotherapy could help elucidate mechanisms of synergy and resistance.
Anti-BCMA CAR-T cell therapies have shown high response rates (> 70%) and median PFS of 8.8 to 12.9 months, but their use often necessitates bridging therapy during manufacturing, in 40–50% of cases [18, 19, 28]. In this context, chemotherapy-based debulking may represent a practical option for disease control while awaiting CAR-T infusion. Moreover, emerging combinations of BsAbs with IMiDs, proteasome inhibitors, or even other BsAbs have been explored in clinical trials with promising results [29, 30]. Whether debulking chemotherapy can be integrated into such regimens to improve outcomes in patients with high tumor burden or EMD remains an open question.