The drug being tested in this study is called Ixazomib. Ixazomib is being tested to treat people who have relapsed and/or refractory multiple myeloma (RRMM). This study will compare the efficacy and safety in participants who take ixazomib and dexamethasone to pomalidomide and dexamethasone. It is an open-label, phase 2 study that, on the basis of a prespecified go/no-go decision rule, will progress to a phase 3 registrational study.