Efficacy and safety of elranatamab in patients with relapsed or refractory multiple myeloma: A US subgroup analysis from MagnetisMM-3

INTRODUCTION: Elranatamab, approved for relapsed or refractory multiple myeloma, demonstrated deep, durable responses and manageable safety in patients without prior B-cell maturation antigen (BCMA)-directed therapy (BCMA-naive) in MagnetisMM-3 (NCT04649359). This post hoc analysis evaluated efficacy and safety in the US subgroup.

METHODS: Following step-up dosing, patients received 28-day cycles of elranatamab 76 mg once weekly. After ≥6 cycles, patients with partial response or better persisting for ≥2 months transitioned to every 2 weeks, then to every 4 weeks after ≥6 every-2-week cycles. This analysis included all US-enrolled BCMA-naive patients who received ≥1 elranatamab dose.

RESULTS: Of the 123 evaluable patients, 47 were enrolled in the United States (38.2%). At a median follow-up of 39.6 months, the objective response rate was 66.0% (95% CI, 50.7-79.1); 42.6% (95% CI, 28.3-57.8) achieved complete response or better. Median (95% CI) duration of response, progression-free survival, and overall survival were 40.8 (24.0-not estimable [NE]), 27.3 (4.3-NE), and 43.6 (14.9-NE) months, respectively. Common (≥60%) treatment-emergent adverse events (any grade; grade 3/4) included infections (70.2%; 42.6%), fatigue (61.7%; 8.5%), and cytokine release syndrome (61.7%; 0%). Twenty-two patients switched from once weekly to every-2-week dosing, then eight switched from every-2-week to every-4-week dosing. Of 18 responders who switched from once weekly to every-2-week dosing and eight responders who further reduced to every 4 weeks, 77.8% and 87.5%, respectively, maintained or improved their response for ≥6 months thereafter.

CONCLUSION: Elranatamab demonstrated durable responses and manageable safety in the heavily pretreated US subgroup, consistent with the overall MagnetisMM-3 BCMA-naive population.