This is a non-interventional observational study aiming to evaluate the quality of life, efficacy, and safety of advanced immuno-oncology agents versus conventional immuno-oncology therapies in patients with relapsed or refractory multiple myeloma. A total of 174 participants are expected to be enrolled in this study. The study consists of three parts: Part 1 is the screening and enrollment phase, during which inclusion and exclusion criteria will be assessed for individuals who have agreed to participate in the study. Eligible participants will be enrolled, and data will be collected on their prioritized treatment value criteria. Part 2 is the treatment phase, during which participants will receive either conventional immuno-oncology therapy or advanced immuno-oncology agents. Participants will visit the site on Day 1 of each treatment cycle to complete patient-reported outcomes (PROs), and efficacy and safety assessments will be conducted. Part 3 is the end-of-study visit, during which PROs will again be collected, along with final efficacy and safety assessments. Additionally, for exploratory purposes, bone marrow and peripheral blood samples will be collected from participants at Seoul St. Mary's Hospital who have consented to sample collection and provision during the study period.