This study looks at how well and how safe two treatments are for people with a type of blood cancer called multiple myeloma. Multiple myeloma is a cancer of the bone marrow which affects blood cells. The research compares two treatments given before a special procedure called autologous hematopoietic stem cell transplantation (ASCT), which involves using a patient's own stem cells to help fight cancer. The study checks if combination treatment with bortezomib-bendamustine-melphalan (BBM) works better than just using high-dose melphalan (HDM).

To join, you must have experienced the return of multiple myeloma after a first ASCT and received a second ASCT at Uppsala University Hospital (UUH) using BBM or HDM. You cannot participate if you've had certain other treatments like a double ASCT or a stem cell transplant from another person. The study looks at past records, so there are no visits needed.

• This study is for those with relapsed multiple myeloma needing a second ASCT.
• No new treatments will be given as it's based on past records.
• Participants' medical history will be reviewed to compare treatment outcomes.