PET Scans in Patients With Diffuse Large B-Cell Lymphoma Receiving Rituximab, Cyclophosphamide, Doxorubicin, Vincristine, and Prednisone

DISEASE CHARACTERISTICS: Inclusion criteria: * Histologically confirmed diagnosis of CD20+ diffuse large B-cell lymphoma (DLBCL) * Stage I-IV disease * All IPI risk groups * Must be positron emission tomography (PET)-positive * At least one measurable lesion ≥ 15 mm in its shortest axis (greatest transverse diameter) for jugulodigastric and infra-carinal lymph nodes with CT scan (MRI is allowed only if CT scan cannot be performed) * Otherwise the shortest axis (greatest transverse diameter) must be ≥ 10 mm * Lesions should be selected according to the following features: * Clearly measurable in two perpendicular dimensions * From as disparate regions of the body as possible * Include mediastinal and retroperitoneal areas of disease whenever these sites are involved Exclusion criteria: * Secondary DLBCL (in transformation) * Evidence of symptomatic CNS disease PATIENT CHARACTERISTICS: Inclusion criteria: * ECOG or WHO performance status 0-2 * Cardiac ejection fraction ≥ 50% as assessed by echocardiography * Sufficient hematological values, hepatic and renal function * Patient condition, compliance, and geographic proximity must allow proper staging and completion of treatment and follow-up * Not pregnant or nursing * Negative pregnancy test * Fertile patients must use effective contraception during and for 12 months after completion of study therapy Exclusion criteria: * Prior or concurrent hematological malignancies * Patients who have had prior solid organ tumors that required no treatment over the past 5 years and are currently disease-free are allowed * Unstable cardiac disease within the past 6 months * Any serious underlying medical condition (at the judgment of the investigator) that could impair the ability of the patient to participate in the study (e.g., active autoimmune disease, uncontrolled diabetes, HIV- and hepatitis-infection) * Known hypersensitivity to any component of the study drugs PRIOR CONCURRENT THERAPY: Exclusion criteria: * Prior chemotherapy, radiotherapy, or immunotherapy (e.g., rituximab) for lymphoma * Prior anthracycline treatment * Concurrent radiotherapy * Concurrent regular corticosteroids in the past 4 weeks * Doses ≤ 20 mg/day of prednisone for indications other than lymphoma or lymphoma-related symptoms allowed * Concurrent drugs contraindicated for use with the study drugs according to the Swissmedic-approved product information * Other concurrent experimental drugs or other anticancer therapy