Bortezomib in Treating Patients With Multiple Myeloma Who Have Undergone an Autologous Peripheral Blood Stem Cell Transplant

DISEASE CHARACTERISTICS: Diagnosis of multiple myeloma Must have completed high-dose melphalan and autologous peripheral blood stem cell transplantation Transplant must have been completed 30-120 days ago Must not be receiving maintenance therapy Patients must have received 200 mg/m² of melphalan intravenously as a conditioning regimen (no dose reduction allowed) No evidence of amyloidosis No available donor PATIENT CHARACTERISTICS: ECOG performance status (PS) 0-2 or Karnofsky PS 60-100% Absolute neutrophil count > 1,500/mm^3 Platelet count > 75,000/mm^3 Bilirubin ≤ 1.5 times upper limit of normal Transaminase ≤ 3 times upper limit of normal Not pregnant or nursing Negative pregnancy test Fertile patients must use effective contraception Must have a negative HIV test No baseline neurological disease > grade I No cranial nerve palsy No demonstrated resistance to bortezomib No history of allergic reactions attributed to bortezomib, boron, or mannitol No cardiac arrhythmia No unstable angina pectoris No symptomatic congestive heart failure No ongoing or active infection No other uncontrolled illness No psychiatric illness or social situations that would limit compliance with study requirements PRIOR CONCURRENT THERAPY: See Disease Characteristics No other concurrent anticancer therapies or agents No other concurrent investigational agents Not receiving maintenance therapy after prior stem cell transplantation on another clinical trial