Dual-targeting bispecific antibodies against extramedullary myeloma: A hypothesis-driven commentary.

Extramedullary multiple myeloma (EMD) remains a high-risk clinical entity with limited responsiveness to currently available therapies, including single-agent T-cell-redirecting approaches. The phase 2 RedirecTT-1 study evaluating dual targeting of GPRC5D (talquetamab) and BCMA (teclistamab) demonstrated unexpectedly high response rates in patients with relapsed/refractory disease and true EMD, suggesting a potential strategy to overcome established resistance mechanisms. While cross-trial comparisons should be interpreted with caution given the single-arm design, these findings highlight the promise of dual antigen targeting in this refractory population. This commentary explores potential biological explanations for the observed efficacy. Specifically, we propose three biological mechanisms: reduction of antigen escape through increased targeting breadth, enhanced immune synapse formation leading to more effective T-cell activation, and modulation of T-cell exhaustion via distributed signaling. These hypotheses remain speculative and require validation through additional studies, including longitudinal immune profiling and single-cell analyses. Notwithstanding these encouraging results, treatment is associated with substantial toxicity, particularly a high incidence of serious infections, underscoring the need for optimized dosing strategies and rigorous supportive care. Future studies should focus on identifying predictive biomarkers, confirming clinical benefit, and refining treatment schedules to balance efficacy with safety.