Inclusion Criteria:

- Diagnosis of intermediate or advanced multiple myeloma meeting criteria for at least
1 2 following:

- Intermediate- to high-M-component production rates (immunoglobulin [Ig]G > 5 g/dL or
IgA > 3 g/dL or urine M component > 4 g/24 hours)

- More than one osteolytic bone lesion or radiographic evidence of diffuse osteoporosis

- β-2 microglobulin > 3

- Nonsecretory myeloma if bone marrow plasmacytosis is greater than 30%

- Must have undergone autologous peripheral blood stem cell transplantation within the
past 3-4 months

- Age 18 to 69 years old

- Absolute neutrophil count ≥ 1,000/mm^3

- Platelet count ≥ 30,000/mm^3

- SGOT or SGPT ≤ 300 IU

- Bilirubin ≤ 2 mg/dL

- Creatinine ≤ 2.0 mg/dL

- Creatinine clearance ≥ 30 mL/min

- Negative pregnancy test

- Fertile patients must use effective contraception

Exclusion Criteria:

- concurrent major cardiac disease that would preclude study participation

- concurrent major pulmonary disease that would preclude study participation

- pregnant or nursing

- peripheral neuropathy ≥ grade 2

- history of hypersensitivity to bortezomib, boron, or mannitol

- concurrent major gastrointestinal or bladder disease that would preclude study
participation

- concurrent major neurologic or psychiatric disease that would preclude study
participation

- dementia or significantly altered mental status that would preclude giving informed
consent

- prior interferon post-transplantation

- prior thalidomide post-transplantation

- prior chemotherapy post-transplantation

- prior radiotherapy post-transplantation

- prior investigational therapy post-transplantation

- prior bortezomib

- prior therapy for myeloma post-transplantation

- other concurrent anti-myeloma therapy

- other concurrent investigational therapy