Standard Maintenance POMP/D Plus Ixazomib Maintenance Therapy in Adult Patients With Acute Lymphoblastic Leukemia, Lymphoblastic Lymphoma or Mixed Phenotype Acute Leukemia in Complete Remission (CR)

Inclusion criteria: * Male or female patients 18 years or older. * Have B-precursor, T cell ALL, MPAL or LBL in CR following therapy and receiving maintenance therapy. Patients with persistent minimal residual disease and/or in complete remission with incomplete platelet recovery are not eligible. * Prior therapy: Should have achieved CR following the induction and intensification phases of treatment, with no limit on the number of prior treatment regimens, and started treatment with POMP/D maintenance. Patients who achieved CRp or CR with persistence of minimal residual disease are not eligible. * Patients are eligible after allogeneic stem cell transplantation. * Eastern Cooperative Oncology Group (ECOG) performance status 0-2. * Patients must meet the following clinical laboratory criteria: * 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 \> 30 mL/min. * Absolute neutrophil count (ANC) \> 1,000/cmm and platelets \> 75,000/cmm. * Patient has a life expectancy of at least six months. * Patients must be at least two weeks from major surgery, radiation therapy, participation in other investigational trials and have recovered from clinically significant toxicities of these prior treatments. * Patients should be on stable doses of 6-mercaptopurine, methotrexate, vincristine and prednisone/dexamethasone as part of the POMP/D regimen, for a minimum of eight weeks PRIOR to starting ixazomib treatment. * Patients should have at least six months of therapy with the POMP/D regimen remaining prior to starting IXAZOMIB (MLN9708). * Female patients who: * Are postmenopausal for at least one year before the screening visit, OR * Are surgically sterile, OR * If they are of childbearing potential, agree to practice two effective. methods of contraception, at the same time, from the time of signing the informed consent form 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 subject. (Periodic abstinence \[e.g., calendar, ovulation, symptothermal, postovulation methods\] and withdrawal are not acceptable methods of contraception.) * Male patients, even if surgically sterilized (i.e., status postvasectomy), must agree to one of the following: * Agree to practice effective barrier contraception during the entire study treatment period and through 90 days after the last dose of study drug, OR * 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 subject. (Periodic abstinence (e.g., calendar, ovulation, symptothermal, postovulation methods\] and withdrawal are not acceptable methods of contraception.) Exclusion criteria: * Systemic treatment, within 14 days before study enrollment, with strong CYP3A inducers (rifampin, rifapentine, rifabutin, carbamazepine, phenytoin, phenobarbital), or use of ginkgo biloba or St. John's wort. * Uncontrolled intercurrent illness including, but not limited to ongoing or active infection, symptomatic congestive heart failure, or psychiatric illness/social situations that would limit compliance with study requirements. Patients should not have evidence of active infection. * Inability to swallow oral medication, inability or unwillingness to comply with the drug administration requirements, or GI procedure that could interfere with the oral absorption or tolerance of treatment. * Active chronic graft vs. host disease requiring therapy. * Patient has ≥ grade 2 peripheral neuropathy. * Participation in clinical trials with other investigational agents not included in this trial, within 14 days of the trial start and throughout the duration of this trial. * Failure to have fully recovered (i.e., \< grade 1 toxicity) from the reversible effects of prior chemotherapy. * Evidence of current uncontrolled cardiovascular conditions, including uncontrolled hypertension, uncontrolled cardiac arrhythmias, symptomatic congestive heart failure, unstable angina, or myocardial infarction within the past six months. * Any serious medical or psychiatric illness that could, in the investigator's opinion, potentially interfere with treatment completion according to this protocol. * Known allergy to any of the study medications, their analogues or excipients in the various formulations of any agent. * Diagnosed or treated for another malignancy within two years before study enrollment or previously diagnosed with another malignancy and have any evidence of residual disease. Patients with nonmelanoma skin cancer or carcinoma in situ of any type are not excluded if they have undergone complete resection. * Female patients who are breastfeeding or have a positive serum pregnancy test during the screening.