Combination Chemotherapy and Donor Stem Cell Transplant Followed by Ixazomib Citrate Maintenance Therapy in Treating Patients With Relapsed High-Risk Multiple Myeloma

PRIMARY OBJECTIVES: I. Safety of BEAM (carmustine, cytarabine, etoposide, melphalan) allogeneic transplant within 100 days, defined as the day 100 transplant related mortality (TRM). II. Safety of oral ixazomib maintenance therapy from day 100 post allogeneic transplant up to 2 years, defined by the incidence of grade III-IV acute (or overlap) graft-versus-host disease (GvHD) and grade III-IV ixazomib related toxicity. OUTLINE: BEAM CONDITIONING REGIMEN: Patients receive carmustine on day -6, cytarabine and etoposide on days -5 to -2, and melphalan on day -1. PERIPHERAL BLOOD STEM CELL TRANSPLANT: Patients undergo allogeneic peripheral blood stem cell transplantation on day 0. GVHD PROPHYLAXIS: Patients receive tacrolimus intravenously (IV) or orally (PO) on days -2 to at least 6 months with a taper as early as 3 months post-transplant and methotrexate IV on days 1, 3, 6, and 11. MAINTENANCE THERAPY: Beginning between days 100 and 180 post-transplant, patients receive ixazomib PO on days 1 and 14 or days 1, 8, and 15 if the principal investigator deems it medically important. Treatment repeats every 28 days for up to 24 cycles in the absence of disease progression or unacceptable toxicity. After completion of study treatment, patients are followed up at 30 days through 4 months post last dose of ixazomib.