The goal of this clinical research study is to learn if there is a difference in transplant outcomes between two different doses of melphalan given in combination with fludarabine followed by transfusion of a related or unrelated volunteer donor's peripheral blood or bone marrow progenitor cells (allogeneic stem cell transplant) in patients with multiple myeloma. This study will also look at whether treatment with a antibody called rituximab against a specific type of lymphocyte (B cell) will reduce the risks of developing graft versus host disease after transplant. The safety of these treatments will also be compared.

Fludarabine is a chemotherapy drug that is used in various diseases. Melphalan is a chemotherapy drug that has been widely used in the treatment of multiple myeloma for many years.

Before beginning therapy, patients will have a complete work-up. This includes a bone marrow aspiration and biopsy, bone survey, blood tests, and tests to check the heart and lung function. All patients will receive tacrolimus and methotrexate to prevent graft-versus-host disease.

Patients in this study will be randomly picked (as in the toss of a coin) to be in one of two treatment groups. There is an equal chance that a patient will be in either group.

Patients in the first group will receive fludarabine through the vein every day for four days. On the fourth day, patients will receive a dose of melphalan through the vein over 20 minutes. On the following day, patients will receive the donor cells as an infusion through their catheter.

Patients in the second group will receive fludarabine through the vein every day for four days. Patients in this group will receive a lower dose of melphalan through the vein over 20 minutes. After the last dose of fludarabine, patients will receive the donor cells as an infusion through their catheter the next day.

If you have an unrelated or a mismatched donor, you will receive the drug ATG (Thymoglobulin) by vein over 6 hours on Days -3, -2, and -1 (the 3 days before the transplant), to prevent graft versus host disease (GVHD) and to help engraftment.

Patients in both group will be receiving the monoclonal antibody called rituximab weekly starting on the fifth day before the stem cell transplant for a total of 4 doses.

Patients will remain in the hospital for about 4-6 weeks and in Houston Medical Center area at least 100 days after transplantation.

Patients whose disease gets worse will be taken off study. These patients will continue to be followed for survival.

This is an investigational study. All of the drugs used in this study are commercially available. The FDA has approved melphalan for the treatment of myeloma. Fludarabine is not approved for the treatment of myeloma but has been used for years as a way to prepare patients for transplant. About 30 to 60 patients will take part in this study. About 45 patients will be enrolled at M. D. Anderson.

Inclusion Criteria:

1. Patients with Multiple Myeloma in any of the following disease categories: a) Primary Refractory considered poor candidate for autologous transplant, b) Remission Consolidation in patients with Chromosome 13 abnormalities or plasma cell leukemia, c) All relapsing patients.
2. Age up to 70 years.
3. Related or unrelated donor who is HLA-compatible in at least 9/10 alleles (A,B, C, DRB1 and DQ) by molecular techniques.
4. Zubrod Performance Score (PS)<2.
5. Life expectancy is not severely limited by concomitant illness. Left ventricular ejection fraction >40%. No uncontrolled arrhythmias or symptomatic cardiac disease. Forced expiratory volume in 1 second (FEV1), forced vital capacity (FVC) and diffusing capacity of the lungs for carbon monoxide (DLCO) >40%.
6. Patient and donor or guardian willing and able to sign informed consent.

Exclusion Criteria:

1) Patients with active central nervous system (CNS) disease are ineligible for this study as documented by clinical symptoms and/or testing.

The end of active treatment was the day of the drug administration of Rituximab on Day+16. Study participation was from baseline to 100 days after transplantation. Overall study period was March 2002 to May 2013.