Arsenic Trioxide and Dexamethasone in Treating Patients With Recurrent or Refractory Stage II or Stage III Multiple Myeloma

DISEASE CHARACTERISTICS: * Diagnosis of stage II or III multiple myeloma * Refractory myeloma defined as progressive disease (more than 25% increase in M protein or in radiographic findings of nonsecretory myeloma) despite up to 3 courses of prior cytotoxic chemotherapy * No more than 3 prior cytotoxic regimens * No more than 1 prior high-dose cytotoxic regimen with stem cell transplantation * History of disease progression after prior steroid antimyeloma therapy * No smoldering myeloma * Measurable disease based on presence of serum and urine M protein and/or measurable plasmacytoma PATIENT CHARACTERISTICS: Age: * Over 18 Performance status: * Karnofsky 70-100% Life expectancy: * At least 3 months Hematopoietic: * Absolute granulocyte count greater than 1,200/mm\^3\* * Platelet count greater than 75,000/mm\^3\* * Hemoglobin greater than 10 g/dL\* NOTE: \*Unless due to multiple myeloma Hepatic: * Bilirubin no greater than 2 times upper limit of normal (ULN) * SGOT and SGPT no greater than 2 times ULN Renal: * Creatinine no greater than 1.5 times ULN Cardiovascular: * Absolute QT interval less than 460 msec in the presence of normal potassium and magnesium levels * No significant underlying cardiac dysfunction * No conduction defects * No unstable angina * No congestive heart failure * No New York Heart Association class II-IV cardiac disease * No myocardial infarction within the past 6 months Other: * No preexisting grade 2 or greater neurotoxicity/neuropathy * No other malignancy within the past 5 years except curatively treated carcinoma in situ of the cervix or nonmelanoma skin cancer * No uncontrolled diabetes mellitus * No active serious infection uncontrolled by antibiotics * No history of grand mal seizures (other than infantile febrile seizures) * Not pregnant or nursing * Negative pregnancy test * Fertile patients must use effective contraception PRIOR CONCURRENT THERAPY: Biologic therapy: * See Disease Characteristics * See Chemotherapy * At least 28 days since prior biologic therapy Chemotherapy: * See Disease Characteristics * At least 28 days since prior cytotoxic chemotherapy, including high-dose cytotoxic regimen with stem cell transplantation * No other concurrent cytotoxic chemotherapy Endocrine therapy: * See Disease Characteristics Radiotherapy: * At least 28 days since prior radiotherapy except for focal radiation for symptom control Surgery: * Not specified