Rituximab With or Without Lenalidomide in Treating Patients With Previously Untreated Follicular Lymphoma

DISEASE CHARACTERISTICS: * Histologically confirmed follicular lymphoma * Stage III or IV disease OR stage II disease not suitable for radiotherapy * Grades 1, 2, or 3a disease * Previously untreated disease * CD20-positive disease * Patients in need of systemic therapy, meeting at least 1 of the following criteria: * Symptomatic enlarged lymph nodes, spleen, or other lymphoma manifestations * Bulky disease ≥ 6 cm in long diameter * Clinically significant progression over at least 6 months of any tumor lesion * Anemia (hemoglobin \< 100 g/L) or thrombocytopenia (platelet count \< 100 x 10\^9/L) due to lymphoma * Clinically significant progressive decrease in hemoglobin or platelet count due to lymphoma * B-symptoms, weight loss \> 10% within the past 6 months, drenching night sweats, or fever \> 38°C not due to infection * At least one two-dimensionally measurable lesion with longest transverse diameter \> 10 mm * Paraffin-embedded tumor tissue available * No known CNS involvement PATIENT CHARACTERISTICS: * WHO performance status 0-2 * EF ≥ 50% for patients with a history of cardiac disease or older than 70 years * Neutrophil count ≥ 1.5 x 10\^9/L * Platelet count ≥ 100 x 10\^9/L * Bilirubin ≤ 1.5 x upper limit of normal (ULN) (unless due to Gilbert syndrome) * ALT ≤ 2.5 x ULN * Alkaline phosphatase ≤ 2.5 x ULN * Creatinine clearance ≥ 30 mL/min * Not pregnant or nursing * Negative pregnancy test * Fertile patients must use effective contraception 4 weeks prior to, during, and for 12 months after completion of study therapy * Must be compliant and geographically proximal to allow for proper staging and follow-up * No serious underlying medical condition, at the judgment of the investigator, which could impair the ability of the patient to participate in the trial (e.g., active autoimmune disease or uncontrolled diabetes) * No malignancy within the past 3 years except for adequately treated carcinoma in situ of the cervix or localized nonmelanoma skin cancer * No psychiatric disorder precluding understanding information of trial-related topics, giving informed consent, or interfering with compliance for oral drug intake * No known hypersensitivity to trial drugs or hypersensitivity to any other components of the trial drugs * No known HIV positivity or hepatitis C infection * No serological evidence of current or past hepatitis B infection, unless the serological findings are clearly due to vaccination PRIOR CONCURRENT THERAPY: * No prior systemic therapy for this disease * At least 3 months since prior radiotherapy * At least 30 days since prior treatment in another clinical trial * At least 4 weeks since prior and no concurrent corticosteroids unless administered as prophylaxis in at-risk patients for ≤ 3 days or at a dose equivalent to prednisone ≤ 15 mg/day, for indications other than lymphoma or lymphoma-related symptoms * No concomitant drugs contraindicated for use with the trial drugs * No other concurrent experimental drugs or anticancer therapy * No other concurrent investigational treatments