This study compares two treatments for multiple myeloma, a type of blood cancer. Patients who have had an autologous stem cell transplant (using their own stem cells) can join the study. They will receive either elranatamab injections at the clinic or lenalidomide pills at home. Elranatamab is a special antibody that helps the body's immune cells attack cancer cells. The study will last about five years.

• Participation lasts approximately five years.
• Elranatamab is given as injections, while lenalidomide is taken orally at home.
• Participants must have had a stem cell transplant and meet specific health criteria.

Eligibility: To join, you must have multiple myeloma with certain health conditions and must not be pregnant. Patients must have had a transplant recently and be in good health. Some conditions like plasma cell leukemia or active infections will exclude participation. This study aims to see which treatment works better for patients after transplant.