Korean Post Marketing Surveillance for ELREXFIO (Elranatamab).

Inclusion Criteria: * Patients who have been prescribed ELREXFIO (Elranatamab) by their physician as monotherapy for the treatment of adult patients with relapsed or refractory multiple myeloma, who have received at least three prior therapies, including a proteasome inhibitor, an immunomodulatory agent, and an anti-CD38 monoclonal antibody, and have demonstrated disease progression on the last therapy. * Patients with evidence of a personally signed and dated informed consent/assent document indicating that the patient (or a legally acceptable representative) has been informed of all pertinent aspects of the study. Exclusion Criteria: * Patients with contraindication according to locally approved label of ELREXFIO (Elranatamab) * Any patients (or a legally acceptable representative) who does not agree that Pfizer and companies working with Pfizer use his/her information