This clinical trial is focused on studying a condition called Relapsed or Refractory Multiple Myeloma (RRMM), which is a type of blood cancer that has returned or is not responding to treatment. The study will compare a new treatment called ABBV-383 with other standard treatments that are currently available. ABBV-383 is a type of medication known as a monoclonal antibody, which is designed to target specific proteins on cancer cells. The purpose of the study is to evaluate how effective and safe ABBV-383 is when used alone in treating adults with RRMM who have already tried at least two other treatments.

Participants in the study will receive either ABBV-383 or one of the standard available therapies, which may include medications like Dexamethasone, Bortezomib, Carfilzomib, Pomalidomide, Selinexor, or Elotuzumab. Some participants may also receive a placebo. The study will last for up to 12 months, during which participants will be monitored regularly to assess their response to the treatment and any side effects they may experience. The study aims to understand how well the treatments work in stopping the progression of the disease and improving overall survival rates.

Throughout the study, participants will undergo various assessments to track their health and the effectiveness of the treatment. These assessments will include regular check-ups and tests to measure the size and activity of the cancer. The study will also collect information on how the treatment affects participants’ quality of life, including their physical functioning and fatigue levels. The results of this study will help determine if ABBV-383 can be a beneficial treatment option for people with RRMM.