Antithymocyte Globulin Compared With Supportive Care in Treating Patients With Myelodysplastic Syndrome

DISEASE CHARACTERISTICS: Histologically or cytologically confirmed early myelodysplastic syndrome (MDS) with less than 10% bone marrow blasts Refractory anemia (RA) RA with excess blasts (RAEB) Hypocellular myelodysplasia Low or intermediate-1 prognostic risk Transfusion-dependent Need for 2 or more units of red blood cells or platelets per month for 2 or more months prior to study OR History of prior transfusions and 2 consecutive (at least 21 days apart) hemoglobin levels less than 8.0 g/dL or platelet counts less than 20,000/mm^3 during the past 2 months Hemoglobin no greater than 12.0 g/dL after prior transfusion No myelosclerosis occupying more than 30% of bone marrow space No RA with ringed sideroblasts, RAEB in transformation, or chronic myelomonocytic leukemia No therapy-related MDS No history of immune-related hematologic disorder (e.g., idiopathic thrombocytopenic purpura) PATIENT CHARACTERISTICS: Age: 18 and over Performance status: ECOG 0-2 Life expectancy: At least 3 months Hematopoietic: See Disease Characteristics No other causes of cytopenia unrelated to MDS (e.g., gastrointestinal blood loss) Iron present on marrow examination OR Transferrin saturation at least 20% and ferritin at least 50 ng/mL Hepatic: Bilirubin no greater than 2 mg/dL OR SGOT/SGPT no greater than 2 times normal No active or chronic hepatitis B or C Renal: Creatinine no greater than 2 mg/dL Cardiovascular: No symptomatic cardiac disease No congestive heart failure (even if medically controlled) No myocardial infarction within the past 6 months Pulmonary: No severe pulmonary disease If history of pulmonary insufficiency, must have pO_2 at least 90 mm/Hg on room air or pCO_2 no greater than 40 mm/Hg Other: No history of unresolved B12 or folate deficiency since diagnosis of MDS No untreated acute or chronic infection (afebrile for 7 days without antibiotics prior to study) No active or chronic HIV No concurrent cytomegalovirus infection No other malignancy within the past 2 years except adequately treated localized squamous cell or basal cell skin cancer or carcinoma in situ of the cervix No concurrent drug or alcohol abuse No significant medical or psychosocial problems No known allergy to rabbit protein Not pregnant or nursing Negative pregnancy test Fertile patients must use effective contraception PRIOR CONCURRENT THERAPY: Biologic therapy: At least 8 weeks since prior biologic agents, colony-stimulating factors, or epoetin alfa for MDS At least 8 weeks since other prior investigational biologic agents No prior or concurrent bone marrow transplantation No concurrent epoetin alfa No concurrent growth factors except filgrastim (G-CSF) or sargramostim (GM-CSF) for neutropenic fevers No other concurrent biologic agents Chemotherapy: At least 8 weeks since prior cytotoxic drugs for MDS Concurrent chemotherapy for clinical indications of disease progression or leukemic transformation allowed Endocrine therapy: At least 8 weeks since prior androgenic hormonal therapy for MDS At least 8 weeks since prior danazol for MDS Radiotherapy: No prior radiotherapy Surgery: No prior organ transplantation Other: At least 8 weeks since prior investigational drugs At least 8 weeks since prior immunosuppressive drugs or other drugs for MDS No concurrent immunosuppressive therapy No other concurrent experimental drugs