This study had an major amendment in 12/2006 introducing risk stratified sequential treatment (RSST). The modified protocol is registered with NCT00590447.

Post-transplantation lymphoproliferative disorder (PTLD) develops in one to ten per cent of transplant recipients and can be EBV-associated. To improve long-term efficacy after rituximab monotherapy and to avoid the toxicity of CHOP seen in first-line treatment, the investigators initiated an international multicentre phase II trial to test whether the subsequent application of rituximab and four courses of three-weekly CHOP would improve the outcome of patients with PTLD: PTLD-1, sequential treatment (ST).

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