Phase 2 Study to Evaluate the Oral Combination of Ixazomib (MLN9708) With Cyclophosphamide and Dexamethasone in Patients With Newly Diagnosed or Relapsed and/or Refractory Multiple Myeloma

Inclusion Criteria:

Each participant with newly diagnosed multiple myeloma (NDMM) must meet all of the following inclusion criteria to be enrolled in the study:

1. Adult male or female participants 18 years of age or older with a confirmed diagnosis of symptomatic multiple myeloma (MM) according to standard criteria.
2. Participants for whom cyclophosphamide and dexamethasone treatment is appropriate and who are considered not eligible for high-dose therapy (HDT)-stem cell transplantation (SCT) for 1 or more of the following reasons:

   * The participant is 65 years of age or older.
   * The participant is less than 65 years of age but has significant comorbid condition(s) that are, in the opinion of the investigator, likely to have a negative impact on tolerability of HDT-SCT.

Each participant with relapsed and/or refractory multiple myeloma (RRMM) must meet all of the following inclusion criteria to be enrolled in the study:

1. Adult male or female participants 18 years or older with a confirmed diagnosis of symptomatic MM either currently or at the time of initial diagnosis, according to standard criteria, and relapsed and/or refractory disease after 1 to 3 lines of prior therapy. A participant is considered to have refractory disease if disease progression occurred during the treatment period or within 60 days of receiving the last dose of a given therapy. A line of therapy is defined as 1 or more cycles of a single-agent or combination therapy or a sequence of planned treatments such as induction therapy followed by autologous stem cell transplantation (ASCT) and then maintenance therapy.
2. No evidence of graft-versus-host disease for participants who have undergone prior allogeneic stem cell transplantation.

In addition, all participants (NDMM and RRMM) must meet all of the remaining criteria:

1. Participants must have measurable disease defined by at least 1 of the following 3 measurements:

   * Serum M-protein ≥ 1 g/dL (≥ 10 g/L).
   * Urine M-protein ≥ 200 mg/24 hours.
   * Serum free light chain assay: involved free light chain level ≥ 10 mg/dL (≥ 100 mg/L), provided that the serum free light chain ratio is abnormal.
2. Participants must meet all of the following clinical laboratory criteria:

   * Absolute neutrophil count (ANC) ≥ 1000/mm\^3 and platelet count ≥ 75,000/mm\^3. Platelet transfusions to help participants meet eligibility criteria are not allowed within 3 days prior to administration of the study drug.
   * Total bilirubin ≤ 1.5 x the upper limit of the normal range (ULN).
   * Alanine aminotransferase (ALT) and aspartate aminotransferase (AST) ≤ 3 x ULN.
   * Calculated creatinine clearance (CrCL) ≥ 30 mL/min.
3. Eastern Cooperative Oncology Group performance status of 0, 1, or 2.
4. Female participants who:

   * are postmenopausal for at least 1 year before the screening visit, or
   * are surgically sterile, or
   * 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, or
   * agree to practice true abstinence over the period previously described, when this is in line with the preferred and usual lifestyle of the participant. (Periodic abstinence \[ie, calendar, ovulation, symptothermal, postovulation methods\] and withdrawal are not acceptable methods of contraception.), and
   * adhere to any treatment-specific pregnancy prevention guidelines for cyclophosphamide and dexamethasone.
5. Male participants, even if surgically sterilized (ie, status post-vasectomy), who:

   * agree to practice effective barrier contraception during the entire study treatment period and through 90 days after the last dose of study drug, or
   * agree to practice true abstinence over the period previously described, 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.), and
   * adhere to any treatment-specific pregnancy prevention guidelines for cyclophosphamide and dexamethasone.
6. 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.
7. Suitable venous access for the study-required blood sampling.
8. Is willing and able to adhere to the study visit schedule and other protocol requirements.

Exclusion Criteria:

1. Prior treatment for multiple myeloma with either standard of care treatment or investigational regimen (for participants with NDMM only).

   NOTE: Prior treatment with corticosteroids (maximum dose of corticosteroids should not exceed the equivalent of 160 mg of dexamethasone over 14 days. Localized radiation is permitted as long as it is below a therapeutic level and administered at least 14 days prior to the first dose of study treatment.
2. Diagnosis of smoldering MM, Waldenström's macroglobulinemia, POEMS (polyneuropathy, organomegaly, endocrinopathy, monoclonal gammopathy, and skin changes) syndrome, plasma cell leukemia, primary amyloidosis, myelodysplastic syndrome, or myeloproliferative syndrome.
3. Central nervous system involvement.
4. Diagnosed or treated for another malignancy within 2 years before the first dose or previously diagnosed with another malignancy and have any 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. Peripheral neuropathy Grade 1 with pain or Grade 2 or higher peripheral neuropathy of any cause on clinical examination during the Screening period.
6. Known gastrointestinal (GI) disease or GI procedure that could interfere with the oral absorption or tolerance of study drug, including difficulty swallowing.
7. Infection requiring intravenous (IV) antibiotic therapy or other serious infection within 14 days before the first dose of study drug.
8. Ongoing or active infection, known human immunodeficiency virus (HIV) positive, active hepatitis B or C infection.
9. Systemic treatment with strong inhibitors of CYP1A2 (fluvoxamine, enoxacin, ciprofloxacin), strong inhibitors of CYP3A (clarithromycin, telithromycin, itraconazole, voriconazole, ketoconazole, nefazodone, posaconazole) or strong CYP3A inducers (rifampin, rifapentine, rifabutin, carbamazepine, phenytoin, phenobarbital), or use of Ginkgo biloba or St. John's wort within 14 days before the first dose of study treatment.
10. Known allergy to any of the study medications, their analogues, or excipients in the various formulations.
11. Major surgery within 14 days before the first dose of study drug. (Note: kyphoplasty or vertebroplasty is not considered major surgery.)
12. Female participants who are lactating and breastfeeding or have a positive serum pregnancy test during the Screening period.
13. Any serious medical or psychiatric illness that could, in the investigator's opinion, potentially interfere with the completion of treatment according to this protocol.
14. 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.
15. Treatment with any investigational products for reasons other than MM within 30 days before the first dose of study drug.