The purpose of this retrospective study is to collect information about patients who received bortezomib as their first chemotherapy and who responded well to it, but who relapsed afterwards and were treated again with bortezomib a second time after a treatment-free period of at least 6 months. During this non-interventional study (this means that no drug is being tested in this study) the safety and effectiveness (whether it works or not) of bortezomib re-treatment will be evaluated in patients with multiple myeloma. Only data already mentioned in your clinical file will be collected. About 100 adult patients will take part in the study