Previous treatment with ixazomib or pomalidomide Previous treatment with ixazomib, or participation in a study with ixazomib whether treated with ixazomib or not Patients that have previously been treated with ixazomib, or participated in a study with ixazomib whether treated with ixazomib or not Myeloma disease that is refractory to ixazomib treatment Known hypersensitivity to bortezomib, ixazomib, dexamethasone, or ONC Prior treatment with ixazomib Inability to take ixazomib or abatacept Patients that have previously been treated with daratumumab or ixazomib, or participated in a study with ixazomib whether treated with ixazomib or not Patients that have previously been treated with ixazomib, or participated in a study with ixazomib whether treated with ixazomib or not Patients that have previously been treated with ixazomib, or participated in a study with ixazomib whether treated with ixazomib or not Previously treated with ixazomib (excluding comparator or placebo participants not on current treatment with ixazomib) in a Millennium-sponsored study. Participants will be eligible to enter the rollover study when: The participant is on ixazomib monotherapy or on a drug combination with another medication, established while in his/her parent study; and Known allergy to ixazomib, its analogues, or excipients in the various formulations of ixazomib Patients that have previously been treated with ixazomib, or who participated in a blinded study with ixazomib (whether treated with ixazomib or not) Previous treatment with ixazomib, or participated in a blinded study with ixazomib Patients that have previously been treated with ixazomib, or participated in a study with ixazomib whether treated with ixazomib or not; (NOTE: prior ibrutinib treatment is allowed as per: patients with prior exposure to ibrutinib will be allowed if they do not have disease refractory to ibrutinib; patient receiving ibrutinib will be allowed on this trial if they have measurable disease and did not have disease progression while receiving ibrutinib; prior bortezomib treatment is allowed as per: patients with prior exposure to bortezomib will be allowed if they do not have disease refractory to bortezomib) Prior participation in a randomized controlled study that included MLN (ixazomib) in one of the treatment arms independent of whether assigned to MLN (ixazomib) or not Patients that have previously been treated with ixazomib, or participated in a study with ixazomib whether treated with ixazomib or not Previous use of interferon, ixazomib or bortezomib Patients that have previously been treated with ixazomib, or participated in a study with ixazomib whether treated with ixazomib or not