High-Dose Melphalan and a Second Stem Cell Transplant or Low-Dose Cyclophosphamide in Treating Patients With Relapsed Multiple Myeloma After Chemotherapy

RATIONALE: Giving chemotherapy and bortezomib before a peripheral stem cell transplant stops the growth of cancer cells by stopping them from dividing or killing them. Giving colony-stimulating factors, such as G-CSF, and certain chemotherapy drugs, helps stem cells move from the bone marrow to the blood so they can be collected and stored. Chemotherapy is then given to prepare the bone marrow for the stem cell transplant. The stem cells are then returned to the patient to replace the blood-forming cells that were destroyed by the chemotherapy and bortezomib. It is not yet known whether high-dose melphalan given together with a second stem cell transplant is more effective than low-dose cyclophosphamide in treating patients with relapsed multiple myeloma. PURPOSE: This randomized phase III trial is studying giving high-dose melphalan together with a second stem cell transplant to see how well it works compared with low-dose cyclophosphamide in treating patients with relapsed multiple myeloma after chemotherapy.