Anti-thymocyte Globulin and Melphalan in Treating Patients With Relapsed Multiple Myeloma

RATIONALE: Biological therapies, such as anti-thymocyte globulin, may stimulate the immune system in different ways and stop cancer cells from growing. Drugs used in chemotherapy, 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. Anti-thymocyte globulin may also make cancer cells more sensitive to melphalan. Giving anti-thymocyte globulin together with melphalan may kill more cancer cells.

PURPOSE: This phase II trial is studying how well giving anti-thymocyte globulin together with melphalan works in treating patients with relapsed multiple myeloma.

OBJECTIVES:

Primary

\* To evaluate the hematological response rate of anti-thymocyte globulin given in combination with melphalan in patients with relapsed multiple myeloma.

Secondary

* To assess the toxicity and tolerability of this combination in these patients.
* To assess time to disease progression in patients treated with these drugs.
* To assess survival of patients treated with these drugs. OUTLINE: Patients receive anti-thymocyte globulin IV over 6 hours and melphalan IV on day 1. Treatment repeats every 28 days for 6 courses. Patients then receive melphalan alone as above for another 6 courses. Treatment continues in the absence of disease progression or unacceptable toxicity.

After completion of study treatment, patients are followed every 3 months until disease progression and then every 6 months for up to 2 years.

Eligibility Criteria:
DISEASE CHARACTERISTICS:

* Diagnosis of multiple myeloma

  - Relapsed disease
* Must not be a candidate for stem cell transplantation, has refused transplantation, or has had stem cells collected previously
* Measurable disease, defined by ≥ 1 of the following:

  * Serum monoclonal protein ≥ 1.0 g by protein electrophoresis
  * More than 200 mg of monoclonal protein in the urine on 24 hour electrophoresis
  * Serum immunoglobulin free light chain ≥ 10 mg/dL AND abnormal serum immunoglobulin kappa to lambda free light chain ratio
  * Monoclonal bone marrow plasmacytosis ≥ 30% (evaluable disease)

PATIENT CHARACTERISTICS:

* Eastern Cooperative Oncology Group (ECOG) performance status 0-3
* Absolute neutrophil count ≥ 1,000/μL
* Platelet count ≥ 75,000/μL
* Hemoglobin ≥ 8.0 g/dL
* CD4 \> 100/μL
* Creatinine ≤ 3 mg/dL
* Not pregnant or nursing
* Negative pregnancy test
* Fertile patients must use effective contraception
* No active malignancy with the exception of nonmelanoma skin cancer or in situ cervical or breast cancer
* No uncontrolled infection
* No other co-morbidity that would interfere with patient's ability to participate in trial

PRIOR CONCURRENT THERAPY:

* No limit to prior therapy
* At least 4 weeks since prior melphalan or other myelosuppressive agents
* At least 2 weeks since prior non-myelosuppressive agents (e.g., thalidomide or high-dose corticosteroids)
* No concurrent high-dose corticosteroids

  * Concurrent chronic steroids (maximum dose 20 mg/day prednisone equivalent) allowed if they are being given for disorders other than amyloid (e.g., adrenal insufficiency or rheumatoid arthritis)
  * Concurrent continuation of low level/stable steroid doses for replacement or inhalation therapy allowed
* Concurrent bisphosphonates allowed
* No concurrent immunosuppressive medications such as cyclosporine
* No other concurrent investigational treatment
* No concurrent cytotoxic chemotherapy or external-beam radiotherapy\>
* No other concurrent systemic anti-neoplastic therapy including, but not limited to, immunotherapy, hormonal therapy, or monoclonal antibody therapy
* No concurrent prophylactic hematopoietic growth factors (unless for treatment of an established cytopenia)