Gemcitabine Hydrochloride, Cyclophosphamide, Vincristine Sulfate, Prednisolone, and Rituximab in Treating Patients With Newly Diagnosed Diffuse Large B-Cell Lymphoma

DISEASE CHARACTERISTICS: * Histologically confirmed CD20-positive diffuse large B-cell non-Hodgkin lymphoma (DLBCL) according to the current WHO classification, including all morphological variants * Newly diagnosed disease * Bulky stage IA-IV disease * No non-bulky stage IA disease * Measurable disease * Not eligible for CHOP chemotherapy due to impaired cardiac function * Cardiac status that does not allow the administration of 8 courses of R-CHOP chemotherapy, as defined by 1 of the following criteria: * Ejection fraction less than 50% as assessed by either ECHO or MUGA scan * NYHA class III-IV * No high-grade transformation of low-grade lymphoma * No symptomatic central nervous system or meningeal involvement by the lymphoma * No AIDS-related lymphoma PATIENT CHARACTERISTICS: * ECOG performance status 0-3 * Life expectancy \> 3 months * Platelet count \> 100 x 10\^9/L * WBC \> 3 x 10\^9/L * Neutrophils \> 1.5 x 10\^9/L (unless elevated level attributed to bone marrow infiltration by lymphoma) * Serum bilirubin \< 50 μmol/L * Transaminases \< 2.5 times upper limit of normal (unless elevated level attributed to lymphoma) * Glomerular filtration rate \> 30 mL/min * Not pregnant or nursing * Fertile patients must use effective contraception * No other concurrent uncontrolled medical condition * No active malignant disease, other than non-melanotic skin cancer or carcinoma in situ of the uterine cervix, within the past 10 years * No positive serology for HIV * No medical or psychiatric conditions that compromise the patient's ability to give informed consent PRIOR CONCURRENT THERAPY: * No prior chemotherapy, radiotherapy, or other investigational drug for this indication