Rituximab in Treating Patients With Follicular Non-Hodgkin's Lymphoma

DISEASE CHARACTERISTICS: * Histologically confirmed follicular lymphoma * Grade 1, 2, 3a, or 3b disease by WHO staging system * CD20-positive by immunohistochemistry * Previously untreated disease OR meets 1 of the following criteria for response to prior treatment: * Chemotherapy-resistant disease * Relapsed or progressive disease * Stable disease * At least 12 weeks since prior systemic treatment * At least 1 bidimensionally measurable lesion ≥ 11 mm by CT scan or MRI * No transformation to high-grade lymphoma secondary to low-grade follicular lymphoma * No prior or current CNS disease (i.e., CNS lymphoma or lymphomatous meningosis) 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: Age * 18 and over Performance status * WHO 0-2 Life expectancy * Not specified Hematopoietic * Not specified Hepatic * Not specified Renal * Not specified Cardiovascular * Ejection fraction ≥ 50% by echocardiography or MUGA Immunologic * No acute or ongoing infection * No HIV infection * No active autoimmune disease Other * Not pregnant or nursing * Negative pregnancy test * Fertile patients must use effective contraception during and for 12 months after completion of the study treatment * No uncontrolled diabetes mellitus * No other medical condition that would preclude study participation * No other malignancy except nonmelanoma skin cancer or adequately treated carcinoma in situ of the cervix * No other condition (e.g., geographic proximity) that would preclude study compliance and follow-up PRIOR CONCURRENT THERAPY: Biologic therapy * See Radiotherapy * Prior rituximab allowed Chemotherapy * See Disease Characteristics Endocrine therapy * More than 4 weeks since prior regular administration of corticosteroids * Dose equivalent to ≤ 20 mg/day prednisone allowed for conditions other than lymphoma or lymphoma-related symptoms * No concurrent corticosteroids for prevention or treatment of side effects except acute life-threatening side effects Radiotherapy * Prior radiolabeled anti-CD20 therapy (administered alone or in combination with cytostatic drugs) allowed provided patient has achieved partial or complete response after the therapy * At least 12 months since prior anti-CD20 therapy Surgery * Not specified Other * More than 30 days since prior systemic tumor therapy * More than 30 days since prior participation in another clinical trial * No other concurrent anticancer therapy