Melphalan and Amifostine Followed By One or Two Autologous or Syngeneic Stem Cell Transplants and Maintenance Therapy in Treating Patients With Stage II-III Multiple Myeloma

RATIONALE: Giving chemotherapy drugs, such as melphalan, work in different ways to stop the growth of cancer cells, either by killing the cells or by stopping them from dividing. Chemoprotective drugs, such as amifostine, may protect normal cells from the side effects of chemotherapy. Giving chemotherapy with a peripheral stem cell transplant once or twice, using stem cells from the patient or an identical brother or sister, may allow more chemotherapy to be given so more cancer cells are killed. Giving maintenance therapy after a stem cell transplant may kill any cancer cells that remain. It is not yet known which dose of melphalan is more effective in treating multiple myeloma (MM). PURPOSE: This randomized phase III trial is studying two different doses of melphalan to compare how well they work when given together with amifostine followed by one or two autologous or syngeneic stem cell transplants and maintenance therapy in treating patients with stage II-III MM