Phase 1/2 Study of the Combination of Pixantrone, Etoposide, Bendamustine and, in CD20 Positive Tumors, Rituximab in Patients With Relapsed Aggressive Non-Hodgkin Lymphomas of B- or T-cell Phenotype - the P[R]EBEN Study

Inclusion Criteria: * Patients with a histologically confirmed relapse of an aggressive lymphoma of T- or B-cell phenotype (including follicular lymphoma grade 3b). For excluded histological entities see 'Exclusion criteria' * Phase 1 + Phase 2 'fit' patients: * Age 18-70 years at the time of inclusion * ECOG PS 0-1 at protocol entry * Deemed 'fit' by the treating physician * Phase 2 'frail' patients: * Age 71-85 years at the time of inclusion and/or * ECOG PS 2-3 at protocol entry and/or * Deemed 'frail' by the treating physician * At least six months response duration since last given course of treatment * Estimated life expectancy of 3 months or longer * Measurable disease * Hemoglobin ≥ 8 g/dL (≥5 mmol/l) * Platelets ≥ 100 x 109/L; ≥ 75 x 109/L permitted if bone marrow involvement * Absolute neutrophil count ≥ 1.5 x 109/L; ≥ 1.0 x 109/L permitted if documented bone marrow involvement * Serum bilirubin ≤ 1.5 x upper limit of normal (ULN); patients with proven Gilbert's syndrome (≤ 5 x ULN) may be enrolled. * Serum glutamic-oxaloacetic transaminase (AST) and/or serum glutamic-pyruvic transaminase (ALT) ≤ 2.5 x ULN, or ≤ 5 x ULN if elevation is due to hepatic involvement by lymphoma * Serum creatinine ≤ 2 x ULNb * Women of childbearing potential must use safe anticonception (e.g. contraceptive pills, intrauterine devices etc.) during the study and 12 months after the last administration of study drugs * Male patients must use contraception for the duration of the study and 6 months after the last administration of study drugs if his partner is of childbearing potential * Written informed consent Exclusion Criteria: * Patients with primary refractory disease (e.g. progressing under platinum-containing or similar salvage therapy) defined as \< 6 months response duration from last given course of treatment. * High-dose therapy with autologous stem cell rescue within the last 6 months prior to study entry. * Following T-cell lymphoma entities: * T-cell lymphoblastic lymphoma * Hepatosplenic T-cell lymphoma * Extranodal NK/T, nasal type * Subcutaneous panniculitis-like * Primary cutaneous T-cell lymphoma * Primary leukemic T-cell lymphoma * Following B-cell lymphoma entities: * Transformed indolent B-cell lymphomas * Post-transplant B-cell lymphoproliferative disease * HIV-associated B-cell lymphoma * Concurrent severe and/or uncontrolled medical disease which is not lymphoma-related * Left ventricular ejection fraction (LVEF) \< 45% * Suspected or documented central nervous system involvement by NHL * Patients known to be antigen positive for HIV and/or hepatitis B and/or hepatitis C * Patients with active, uncontrolled infections * Vaccination with live, attenuated vaccines within 4 weeks of inclusion * Pregnant and/or breastfeeding women * History of active cancer during the past 5 years, except basal carcinoma of the skin or stage 0 cervical carcinoma * Known hypersensitivity to one or more of the study drugs * Unwillingness or inability to comply with the protocol