Significance of Duration of Maintenance Therapy With Rituximab in Non-Hodgkin Lymphomas

Inclusion Criteria: * Patients with histological verified CD20-positive B-Cell-Lymphoma of the following entities: * Follicular Lymphoma Grade 1 and 2 * Lymphoplasmocytic lymphoma / Immunocytoma (Morbus Waldenström) and small cell lymphocytic lymphoma (CLL without leukemic hemogram) * Marginal zone lymphoma, nodal and extra nodal * Mantle cell lymphoma * No prior therapy with cytotoxics, interferon or monoclonal antibodies * Need for therapy, except mantle cell lymphomas * Stadium III or IV or Stadium with II bulky disease (\> 7 cm diameter, or 3 lesions \> 5 cm) * General condition WHO 0-2 * Age min. 18 years, max. 80 years * Negative pregnancy test, contraceptives mandatory for women of child-bearing age * Actual histology, not older than 6 months required * Written informed consent Exclusion Criteria: * Patients not meeting the inclusion criteria above * Possibility of a primary radiation therapy with curative intention * Pretreatment, except a single, localized radiation therapy (radiation field not larger than 2 adjacent lymph node regions) * Co-morbidities, excluding a therapy according to the protocol: * severe, medicinal not adjustable hypertension * severe limited capacity of the heart (NYHA III or IV), the lung (WHO-Grade III or IV), the liver and kidneys (creatinin \> 2 mg/dl, GOT and GPT or bilirubin 3 x ULN), except if caused by lymphoma * severe, medicinal not adjustable diabetes mellitus * active autoimmune disease * active infection, requiring antibiotic therapy * Patients with proven HIV-infection * Active replicating hepatitis-Infection * Severe psychiatric diseases * Lacking or anticipated non-compliance * Known hypersensitivity against the active components or additives or mouse- proteins * Pregnant or nursing women * Patients with a secondary malignancy or malignant disease in his history if, curative surgery can not be doubtless assured .