ZAR2007: R-CHOP in Folicular Lymphoma Patients no Treated Previously. Consolidation With 90Y Ibritumomab Tiuxetan (Zevalin®) Versus Maintenance Treatment With Rituximab (MabThera®)

Inclusion Criteria: * Folicular Lymphoma CD20-positive, grade 1, 2 or 3a, confirmed in previous 4 months. * Patients no treated previously. * Ann Arbor Stage II, III o IV. * Symptoms or signes wich indicate necesary treatment (GELF criteria): * Ganglionar or extraganglionar mass * B Symptoms * LDH or B2-microglobuline increased * 3 ganglionar territory afected (\> 3 cm) * Esplenomegalia * Compresive syndrome * Pleural/peritoneal effusion * Secondary medular insufiency due to infiltration * Age\> 18 years and \<75 years. * ECOG \< 2 * Adecuate hematological function: Hemoglobin \> 8,0 g/dl (5,0 mmol/L); RAN \>1,5 x 109/L; platelets \> 100 x 109/L * No pregnant women. Women and man should use an appropiate anticonceptive method during the study and one year after * Informed consent Exclusion Criteria: * Transformation in high grade lymphoma * FL grade 3b. * Skin or gastro-intestinal primary lymphoma * History of CNS diseases ( or CNS lymphoma) * Previous treatment * Regulary treatment with corticosteroids (permited \< 20 mg/day prednisone or equivalent). * Previous cancer diseases * Major surgery in 28 days before inclusion in study. * Creatinine \> 2,0 mg/dl (197 mmol/L) * Bilirubin \> 2,0 mg/dl (34 mmol/L), AST (SGOT) \> 3 x upper normal limit. * HIV infection or active infection VHB o VHC \< 4 weeks before inclusion. * Other complicated diseases Criteria investigador: * Life expectancy \< 6 months. * Hipersensibility to Ibritumomab tiuxetan, rituximab, other murines proteins or any excipients. * Treatment in other experimental study in previous 30 days * Any medical o psicologycal condition that can modify the capacity to give the consent