Study of Dexamethasone Plus IXAZOMIB (MLN9708) or Physicians Choice of Treatment in Relapsed or Refractory Systemic Light Chain (AL) Amyloidosis

The drug being tested in this study is called IXAZOMIB. IXAZOMIB was being tested to treat people who have relapsed or Refractory Systemic Light Chain (AL) Amyloidosis.

The study will enroll approximately 177 patients. Participants will be randomly assigned (by chance, like flipping a coin) to one of the two treatment groups:

* IXAZOMIB 4 mg plus Dexamethasone 20 mg * Physician's choice: Participants will receive one of the following treatment options as selected by the physician:

1. Dexamethasone 20 mg 2. Dexamethasone 20 mg + Melphalan 0.22 mg/kg 3. Dexamethasone 20 mg + Cyclophosphamide 500 mg 4. Dexamethasone 20 mg + Thalidomide 200 mg 5. Dexamethasone 20 mg + Lenalidomide 15 mg 6. All participants will be asked to take oral formulation of the drugs. In both treatment arms, each participant will continue to receive sequential cycles of therapy until disease progression, unacceptable toxicity, or until the study is terminated, whichever occurs first. Participants in Arm B receiving melphalan and dexamethasone will be treated to best response plus 2 additional cycles.

This multi-center trial will be conducted worldwide. The overall time to participate in this study is 120 months (10 years), including 84 months of enrollment and 36 months of follow-up after the last participant is enrolled.