Purpose Selinexor, a first-in-class, oral, selective exportin 1 (XPO1) 
inhibitor, induces apoptosis in cancer cells through nuclear retention of tumor 
suppressor proteins and the glucocorticoid receptor, along with inhibition of 
translation of oncoprotein mRNAs. We studied selinexor in combination with 
low-dose dexamethasone in patients with multiple myeloma refractory to the most 
active available agents. Patients and Methods This phase II trial evaluated 
selinexor 80 mg and dexamethasone 20 mg, both orally and twice weekly, in 
patients with myeloma refractory to bortezomib, carfilzomib, lenalidomide, and 
pomalidomide (quad-refractory disease), with a subset also refractory to an 
anti-CD38 antibody (penta-refractory disease). The primary end point was overall 
response rate (ORR). Results Of 79 patients, 48 had quad-refractory and 31 had 
penta-refractory myeloma. Patients had received a median of seven prior 
regimens. The ORR was 21% and was similar for patients with quad-refractory 
(21%) and penta-refractory (20%) disease. Among patients with high-risk 
cytogenetics, including t(4;14), t(14;16), and del(17p), the ORR was 35% (six of 
17 patients). The median duration of response was 5 months, and 65% of 
responding patients were alive at 12 months. The most common grade ≥ 3 adverse 
events were thrombocytopenia (59%), anemia (28%), neutropenia (23%), 
hyponatremia (22%), leukopenia (15%), and fatigue (15%). Dose interruptions for 
adverse events occurred in 41 patients (52%), dose reductions occurred in 29 
patients (37%), and treatment discontinuation occurred in 14 patients (18%). 
Conclusion The combination of selinexor and dexamethasone has an ORR of 21% in 
patients with heavily pretreated, refractory myeloma with limited therapeutic 
options.