Rituximab and Cyclophosphamide in Treating Patients With High Risk, Refractory, or Relapsed Multiple Myeloma

DISEASE CHARACTERISTICS: * Diagnosis of multiple myeloma, meeting 1 of the following criteria: * High-risk disease in first remission, as defined by the following: * Beta-2 microglobulin \> 5.0 mg/dL * Chromosome 13 deletion * Primary refractory disease * Relapsed disease after achieving a response to prior chemotherapy * The following diagnoses are not allowed: * POEMS syndrome * Plasma cell leukemia * Amyloidosis * Nonsecretory myeloma * No evidence of spinal cord compression PATIENT CHARACTERISTICS: Age * Over 18 Performance status * Not specified Life expectancy * Not specified Hematopoietic * Not specified Hepatic * Not specified Renal * Not specified Other * Not pregnant or nursing * Fertile patients must use effective contraception * HIV negative * Has good organ function * Is in good physical condition * No active infection requiring antibiotics * No other malignancy within the past 2 years except basal cell or squamous cell skin cancer or carcinoma in situ of the cervix PRIOR CONCURRENT THERAPY: Biologic therapy * No persistently detectable donor cells after prior allogeneic stem cell transplantation * No prior rituximab Chemotherapy * See Disease Characteristics Endocrine therapy * Not specified Radiotherapy * Not specified Surgery * Not specified Other * At least 28 days since prior therapy