Pentostatin, Cyclophosphamide, Rituximab, and Mitoxantrone in Treating Patients With Chronic Lymphocytic Leukemia or Other Low-Grade B-Cell Cancer

DISEASE CHARACTERISTICS: * Diagnosis of 1 of the following diseases confirmed by a Memorial Sloan-Kettering Cancer Center (MSKCC) pathologist: * Chronic lymphocytic leukemia meeting the following risk criteria as defined by the three-stage Rai system: * Intermediate-risk disease meeting the following criteria for active disease as defined by the NCI Working Group: * Weight loss * Fatigue * Fevers * Evidence of progressive marrow failure * Splenomegaly * Progressive lymphadenopathy * Progressive lymphocytosis with a rapid doubling time, defined as doubling time less than 6 months and absolute lymphocyte count \> 30,000/μL * High-risk disease * Other low grade B-cell neoplasms, including any of the following: * Small lymphocytic lymphoma * Follicular lymphoma * Waldenstrom macroglobulinemia * Marginal zone lymphomas * Mantle cell lymphomas * Transformed lymphoma * Previously treated disease * Must have received prior cytotoxic therapy * Malignant lymphocytes must demonstrate B-cells via immunophenotypic or immunohistochemical analysis NOTE: A new classification scheme for adult non-Hodgkin's lymphoma has been adopted by PDQ. The terminology of "indolent" or "aggressive" lymphoma will replace the former terminology of "low", "intermediate", or "high" grade lymphoma. However, this protocol uses the former terminology. PATIENT CHARACTERISTICS: * Karnofsky performance status 60-100% * Life expectancy \> 8 weeks * Total bilirubin ≤ 2.0 mg/dL (patients with Gilbert disease or autoimmune hemolytic anemia should have an evaluation for other causes of hyperbilirubinemia, but if none are found, may be enrolled regardless of serum bilirubin) * Total creatinine ≤ 2.0 mg/dL OR creatinine clearance \> 50 mL/min * Not pregnant or nursing * Fertile patients must use effective contraception * Normal cardiac ejection fraction ≥ 50% (increased ejection fraction \[at least 5% over rest\]) required for study eligibility * Borderline (40-50%) ejection fraction must undergo a stress echocardiogram or MUGA scan * Patients with autoimmune hemolytic anemia or autoimmune thrombocytopenia are eligible for treatment * Must have undergone consultation with the primary investigator or his/her designee prior to study entry * No significant active infections * No ongoing hepatitis B infection, specifically hepatitis B antigen or surface antigen positivity * Hepatitis B antibody-positive patients are eligible PRIOR CONCURRENT THERAPY: * See Disease Characteristics * The following concurrent medications are allowed: * Intravenous immunoglobulin (IVIG) * Erythropoietin, darbepoetin, filgrastim, or sargramostim * Cyclosporine (only for patients with cellular immune cytopenias \[i.e., pure red cell aplasia\]), with required consultation of the principle investigator or designee * Concurrent prednisone allowed provided it is used as brief courses (≤ 7 days) for inflammatory conditions unrelated to CLL * No concurrent chemotherapy or radiotherapy