One purpose of this study is to evaluate the effectiveness and safety in long term treatment for patients who completed preceding phase I/II study. The other purpose is to evaluate the effectiveness and safety of patients who are re-treated with this drug in recommended dose.

Multiple myeloma is a kind of malignant disease in the organ which produce blood cells such as bone marrow. It has poor prognosis, especially in patients who are relapsed repeatedly. Effective treatment is strongly expected in such relapsed patients in Japan. This is a open label multiple center study to evaluate the effectiveness and safety of bortezomib. This study is an extension or re-treatment study for patients who were administered with bortezomib in preceding Phase I/II study. For extension treatment, the same dose of the previous study will be administered into a vein as a bolus twice weekly followed by a 10-day rest (3-week cycle). For re-treatment, a recommended dose determined in Phase I/II study will be administered in 3-week cycle.

Inclusion Criteria:

• Complete 6 cycles treatment in preceding phase I/II study
• response (CR, PR, MR or NC) was obtained in 6 cycles treatment during the preceding phase I/II study and investigator considers that the patient is expected to have benefit such as antitumor effect, pain relief or improvement of performance state
• Patients who did not have Grade >=3 non-hematologic toxicity or Grade 4 hematologic toxicity during the preceding phase I/II study or extension treatment of this study
• Investigator considers that the patient is expected to have benefit of this drug such as antitumor effect, pain relief or improvement of performance state.

Exclusion Criteria:

• Patient is known to be HBs antigen positive, HCV antibody positive or HIV antibody positive (check is required for patients who received blood product during phase I/II study)
• Patients who receive G-CSF product or blood transfusion within 7 days before the start of treatment
• Disease progress was observed during the phase I/II or this study when patients receive recommended dose
• Patients who suffer Grade >=2 peripheral neuropathy or Grade >=2 neuropathic pain
• Patient has New York Heart Association (NYHA) Class III or IV heart failure, uncontrolled angina, severe uncontrolled ventricular arrhythmias, acute ischemia or active conduction system abnormalities.