Selinexor + Bispecific Antibody

The primary objectives of this study are to determine the safety of single agent Selinexor given with commercial bispecific antibody therapy in patients with Relapsed/Refractory Multiple Myeloma (RRMM) and to determine the MRD negativity rate at 10-5 at 12 months post bispecific antibody therapy. The investigators will enroll 27 patients with RRMM who are receiving commercial bispecific antibody therapy. Patients will be on treatment for 12 months or until disease progression, and will be followed for 24 months. Study assessments include completing a drug diary, having a safety check in call, and have history, clinical assessments, and labs taken. Twenty-seven patients will provide 80% power in a one-sample chi square test for a proportion assuming that the rate of negative MRD at 10-5 at 12 months post bispecific antibody therapy is 25% in historical control and 50% in the SEL+bispecific antibody experimental treatment group, under a one-sided 5% significance level.