Patients receive bortezomib IV weekly for 4 weeks. Treatment repeats every 5 weeks for up to 2 courses in the absence of disease progression or unacceptable toxicity. Patients achieving a response (complete remission, partial remission, or minimal remission) after 2 courses may receive an additional 6 courses of therapy. Patients who achieve stable disease with acceptable toxicities after 2 courses receive bortezomib IV at a higher dose twice weekly for 2 weeks. Treatment with a higher dose of bortezomib repeats every 3 weeks for up to 6 courses.