Sequential Treatment of CD20-positive Posttransplant Lymphoproliferative Disorder (PTLD)

Inclusion Criteria: * PTLD with or without EBV association, confirmed after biopsy or resection * Measurable disease of \> 2 cm in diameter and/or bone marrow involvement * Patients having undergone heart, lung, liver, kidney, pancreas, small intestine transplantation or other or a combination of the organ transplantations mentioned * Karnofsky scale \>50% or ECOG ≤ 3 * Reduction of immunosuppression with or without antiviral therapy * A complete surgical extirpation of tumor was not performed * A radiation therapy was not performed * Effective contraception for women in childbearing age * Patient's written informed consent and written consent for data collection * Patients are \> 18 years (or ≥ 15 years with parental agreement ) Exclusion Criteria: * Life expectancy less than 6 weeks * Karnofsky-scale \<50% or ECOG =3 * Treatment with rituximab before * Known allergic reactions against foreign proteins * Concomitant diseases, which exclude the administration of therapy as outlined by the study protocol * non-compensated heart failure * Dilatative cardiomyopathy * Myocardial infarction during the last 6 months * Severe non-compensated hypertension * Severe non-compensated diabetes mellitus * Renal insufficiency (creatinine more than 3-fold of the upper normal value), not related to lymphoma. * Hepatic insufficiency with transaminase values greater than 3-fold of the normal values and/or bilirubin levels \>3.0 mg/dl, not related to lymphoma * Clinical signs of cerebral dysfunction * Women during the lactation period, pregnant or of childbearing potential not using a reliable contraceptive method * Involvement of the central nervous system by the disease * Severe psychiatric disease * Known to be HIV positive * Missing written informed consent of the patient