Inclusion Criteria:

• Age ≥ 18 years
• Expected survival ≥ 6 months
• Pre-study performance status of 0, 1, or 2 according to the World Health Organization (WHO)
• Newly diagnosed or relapsed/refractory myeloma with histologic confirmation of multiple myeloma by the Department of Pathology at University of Michigan Cancer Center (UMCC)
• Not more than 3 lines of therapy for myeloma for patients with relapsed disease
• Documented Stage II or III multiple myeloma (Durie and Salmon, 1975) prior to initiation of first line therapy
• At least 4 cycles of first line (for newly diagnosed patients) or salvage (for relapsed/refractory patients) prior therapy and in a plateau of at least partial response (Blade et al, 1999) for at least 2 determinations 6 weeks apart
• At least 21 days from day 1 of the last cycle and fully recovered from all toxicities associated with prior surgery, radiation treatments, chemotherapy, or immunotherapy
• Measurable M-proteins with greater than 1 g/dl serum monoclonal protein and/or greater than 0.5 g/24 hour urine light chain excretion

• Acceptable hematologic status within two weeks prior to patient registration, including:

  • Absolute neutrophil count ([segmented neutrophils + bands] x total white blood cell [WBC]) ≥ 1,500/mm3;
  • Platelet counts ≥ 150,000/mm3; these patients will receive total body dose of 75 cGy of Bexxar; or
  • Platelet counts from 100,000/mm3 to 149,000/mm3; these patients will receive a 65 cGy total body dose of Bexxar;
  • In patients previously treated with ASCT, total body dose will be 55 cGy in patients with platelet count > 150,000 and 45 cGy in patients with platelets 100,000-149,000.
• Female patients who are not pregnant or lactating
• Men and women of reproductive potential who are following accepted birth control methods (as determined by the treating physician)
• Patients previously on Phase II drugs if no long-term toxicity is expected, and the patient has been off the drug for three or more weeks with no significant post treatment toxicities observed
• Patients determined to have < 25% bone marrow involvement with myeloma within six weeks of registration (based on bilateral core biopsy).

Exclusion Criteria:

• Patients with impaired bone marrow reserve, as indicated by one or more of the following:

  • Platelet count < 100,000 cells/mm3;
  • Hypocellular bone marrow;
  • Marked reduction in bone marrow precursors of one or more cell lines (granulocytic, megakaryocytic, erythroid);
  • History of failed stem cell collection;
  • Myelodysplastic syndrome (MDS) or evidence of other than myeloma clonogenic abnormalities;
  • Prior radioimmunotherapy;
  • Prior anti-CD20 therapy;
  • Other than myeloma malignancy, except B-cell non-Hodgkin's lymphoma, basal and squamous cell carcinoma of the skin, and cervical and breast cancer in situ, unless patient is cancer free for > 3 years;
  • Central nervous system (CNS) involvement;
  • Patients with known HIV infection;
  • Patients with pleural effusion;
  • Patients with abnormal liver function: total bilirubin > 2.0 mg/dL;
  • Patients with abnormal renal function: serum creatinine > 2.0 mg/dL;
  • Patients who have received prior external beam radiation therapy to > 25% of active bone marrow (involved field or regional);
  • Patients who have received G-CSF or GM-CSF therapy within two weeks prior to treatment;
  • Serious nonmalignant disease or infection which, in the opinion of the investigator and/or the sponsor, would compromise other protocol objectives;
  • Major surgery, other than diagnostic surgery, within four weeks;
  • Presence of anti-murine antibody (HAMA) reactivity. This result must be available prior to receiving treatment for those patients with prior exposure to murine antibodies or proteins.