Carfilzomib, Bendamustine Hydrochloride, and Dexamethasone in Treating Patients With Relapsed or Refractory Multiple Myeloma

PRIMARY OBJECTIVES: I. To determine the maximum tolerated dose (MTD) of carfilzomib in combination with bendamustine (bendamustine hydrochloride) and dexamethasone, up to a maximum bendamustine dose of 90 mg/m\^2. SECONDARY OBJECTIVES: I. To evaluate the safety of carfilzomib in combination with bendamustine and dexamethasone, at the MTD. II. To evaluate the response rate and duration of response of carfilzomib in combination with bendamustine and dexamethasone, in patients with relapsed and or refractory multiple myeloma. OUTLINE: This is a dose-escalation study of carfilzomib and bendamustine hydrochloride. Patients receive dexamethasone orally (PO) or intravenously (IV) over 20 minutes on days 1, 2, 8, 9, 15, 16, 22, and 23 of courses 1-3; on days 1, 2, 15, and 16 of courses 4-12; and on days 1 and 2 of all subsequent courses. Patients also receive bendamustine hydrochloride IV over 10 minutes on days 1 and 2 of courses 1-3 and on day 1 of all subsequent courses and carfilzomib IV over 30 minutes on days 1, 2, 8, 9, 15, and 16 of courses 1-12 and on days 1, 2, 15, and 16 of all subsequent courses. Courses repeat every 28 days in the absence of disease progression or unacceptable toxicity. After completion of study treatment, patients are followed up for 30 days, every 3 months for 1 year, and then every 6 months thereafter.