Lowering the Selinexor Dose within the Pomalidomide and Dexamethasone Combination Regimen Elicits Fewer Side Effects While Comparable Efficacy Against Relapsed/Refractory Multiple Myeloma.

Background: As a novel oral Exportin 1 (XPO1) inhibitor, selinexor at 80 or 100 mg has demonstrated efficacy in treating relapsed/refractory multiple myeloma (RRMM), nonetheless, this dosage has shown poor tolerability.

Objective: To explore the optimal dosage of selinexor, we evaluated the efficacy and safety of 60 vs 40 mg selinexor, combine with regimen comprising pomalidomide and dexamethasone in RRMM.

Design: 21 patients with RRMM were enrolled to receive selinexor (60 or 40 mg once weekly), together with pomalidomide (4 mg/day on days 1-21) and dexamethasone (40 mg once weekly); the SPD-60 group (6 patients) vs SPD-40 group (15 patients).

Methods: The clinical response and efficacy of the two groups were continuously followed up, and statistical analysis was carried out to screen out the dose group with fewer side effects and better efficacy. The primary endpoint was (objective response rates) ORR. The secondary endpoints included treatment safety and tolerability, progression-free survival (PFS) and overall survival (OS).

Results: The ORR of the SPD-60 and SPD-40 groups were 33.3% and 46.7% respectively (=0.773). With a median follow-up of 20.9 months, the median PFS was 6.2 months and the median OS was not achieved across all treated patients. The median PFS for SPD-60 group was 4.3 months, while for SPD-40 was 8.0 months (=0.618). The 1-year OS rate were 66.7% for SPD-60 group and 85.1% for the SPD-40 group (=0.308). The most common hematological adverse events were neutropenia (SPD-60 group 50% vs SPD-40 group 53.3%) and thrombocytopenia (50% vs 46.7%). Fatigue (83.3% vs 40%), infection (50% vs 53.3%), and nausea (83.3% vs 40%) were the most common non-hematologic adverse effects.

Conclusion: The SPD-40 regimen may be more clinically applicable than SPD-60, as it elicited fewer adverse effects while demonstrating equivalent efficacy.

Trial Registration: : NCT04941937.