A Study of Oral Ixazomib Citrate (MLN9708) Maintenance Therapy in Participants With Multiple Myeloma Following Autologous Stem Cell Transplant

The purpose of this study is to determine the effect of ixazomib citrate maintenance therapy on progression-free survival (PFS), compared to placebo, in participants with newly diagnosed multiple myeloma (NDMM) who have had a response (complete response \[CR\], very good partial response \[VGPR\], or partial response \[PR\]) to induction therapy followed by high-dose therapy (HDT) and autologous stem cell transplant (ASCT).

The investigational drug being tested in this study is called ixazomib citrate. Ixazomib citrate is being tested to slow disease progression and improve overall survival in people who have NDMM and who have had any type of positive response to induction therapy followed by HDT and ASCT. This study will look at the effect ixazomib citrate has on the length of time that participants are free of progressive disease (PD) and their overall survival (OS).

The study enrolled 656 participants. Participants were randomly assigned (by chance, like flipping a coin) to one of the two treatment groups-which will remain undisclosed to the participant and study doctor during the study (unless there is an urgent medical need, or if the disease has progressed and the information is required for planning the next treatment):

* Ixazomib citrate 3 mg for the first 4 cycles, then 4 mg for the remaining 22 cycles
* Placebo (dummy inactive pill) - this is a capsule that looks like the study drug but has no active ingredient.

All participants will be asked to take one capsule on Days 1, 8 and 15 of each 28-day cycle, for up to 26 cycles (approximately 24 months).

This multi-center trial will be conducted globally. The overall time to participate in this study is up to 107 months. Participants will make 28 visits to the clinic during the treatment period and will continue to make visits after treatment has ended. During this initial follow up period, participants will be assessed for disease status with follow up every 12 weeks. After the next line of therapy begins, follow-up will occur every 12 weeks until death or termination of the study.

Eligibility Criteria:
Inclusion Criteria:

1. Adult male or female participants 18 years or older with a confirmed diagnosis of symptomatic multiple myeloma according to standard criteria.
2. Documented results of cytogenetics/ fluorescence in situ hybridization (FISH) obtained at any time before transplant, and International Staging System (ISS) staging at the time of diagnosis available.
3. Underwent standard of care (SOC) induction therapy (induction therapy must include proteasome inhibitor (PI) and/or immunomodulating drugs (IMiD)-based regimens as primary therapy for multiple myeloma), followed by a single autologous stem cell transplant (ASCT) with a high-dose melphalan (200 mg/m\^2) conditioning regimen, within 12 months of diagnosis. Vincristine, Adriamycin \[doxorubicin\], and dexamethasone (VAD) is not an acceptable induction therapy for this trial.
4. Started screening no earlier than 75 days after transplant, completed screening within 15 days, and randomized no later than 115 days after transplant.
5. Must have not received post-ASCT consolidation therapy.
6. Documented response to ASCT (PR, VGPR, CR/stringent complete response \[sCR\]) according to IMWG criteria.
7. ECOG performance status of 0 to 2.
8. Female participants who:

   * If they are of childbearing potential, agree to practice 2 effective methods of contraception, at the same time, from the time of signing the informed consent through 90 days after the last dose of study drug, AND
   * Must also adhere to the guidelines of any treatment-specific pregnancy prevention program, if applicable, OR
   * Agree to practice true abstinence, when this is in line with the preferred and usual lifestyle of the participant. (Periodic abstinence \[eg, calendar, ovulation, symptothermal, postovulation methods for the female partner\] and withdrawal are not acceptable methods of contraception.) Male participants, even if surgically sterilized (ie, status postvasectomy), who:
   * Agree to practice effective barrier contraception during the entire study treatment period and through 90 days after the last dose of study drug, AND
   * Must also adhere to the guidelines of any treatment-specific pregnancy prevention program, if applicable, OR
   * Agree to practice true abstinence, when this is in line with the preferred and usual lifestyle of the participant. (Periodic abstinence \[eg, calendar, ovulation, symptothermal, postovulation methods for the female partner\] and withdrawal are not acceptable methods of contraception.)
9. Voluntary written consent must be given before performance of any study-related procedure not part of standard medical care, with the understanding that consent may be withdrawn by the participant at any time without prejudice to future medical care.
10. Suitable venous access for the study-required blood sampling.
11. Is willing and able to adhere to the study visit schedule and other protocol requirements.
12. Must meet the following clinical laboratory criteria at study entry:

    * Absolute neutrophil count (ANC) ≥ 1,000 per cubic milliliter (/mm\^3) and platelet count ≥ 75,000/mm\^3. Platelet transfusions to help participants meet eligibility criteria are not allowed within 3 days before randomization.
    * Total bilirubin ≤ 1.5 \* the upper limit of the normal range (ULN).
    * Alanine aminotransferase (ALT) and aspartate aminotransferase (AST) ≤ 3 \* ULN.
    * Calculated creatinine clearance ≥ 30 milliliter per minute (mL/min).

Exclusion Criteria:

1. Multiple myeloma that has relapsed following primary therapy or is not responsive to primary therapy. For this study, stable disease following ASCT will be considered nonresponsive to primary therapy.
2. Double (tandem) ASCT.
3. Radiotherapy within 14 days before the first dose of study drug.
4. Diagnosed or treated for another malignancy within 5 years before randomization or previously diagnosed with another malignancy with evidence of residual disease. Participants with nonmelanoma skin cancer or carcinoma in situ of any type are not excluded if they have undergone complete resection.
5. Female participants who are lactating and breastfeeding or have a positive serum pregnancy test during the Screening period.
6. Major surgery within 14 days before randomization.
7. Central nervous system involvement.
8. Infection requiring intravenous (IV) antibiotic therapy or other serious infection within 14 days before randomization.
9. Diagnosis of Waldenstrom's macroglobulinemia, POEMS (polyneuropathy, organomegaly, endocrinopathy, monoclonal gammopathy, and skin changes) syndrome, plasma cell leukemia, primary amyloidosis, myelodysplastic syndrome, or myeloproliferative syndrome.
10. Evidence of current uncontrolled cardiovascular conditions, including uncontrolled hypertension, uncontrolled cardiac arrhythmias, symptomatic congestive heart failure, unstable angina, or myocardial infarction within the past 6 months.
11. Systemic treatment with strong cytochrome P450 3A (CYP3A) inducers (rifampin, rifapentine, rifabutin, carbamazepine, phenytoin, phenobarbital), or use of Ginkgo biloba or St. John's wort within 14 days before randomization in the study.
12. Active hepatitis B or C virus infection, or known human immunodeficiency virus (HIV) positive.
13. Comorbid systemic illnesses or other severe concurrent disease which, in the judgment of the investigator, would make the participant inappropriate for entry into this study or interfere significantly with the proper assessment of safety and toxicity of the prescribed regimens (eg, peripheral neuropathy that is Grade 1 with pain or Grade 2 or higher of any cause).
14. Psychiatric illness/social situation that would limit compliance with study requirements.
15. Known allergy to any of the study medications, their analogues, or excipients in the various formulations of any agent.
16. Inability to swallow oral medication, inability or unwillingness to comply with the drug administration requirements, or gastrointestinal (GI) procedure that could interfere with the oral absorption or tolerance of treatment.
17. Treatment with any investigational products within 60 days before the first dose of the study drug regimen.