Inclusion Criteria:  The informed consent form must be signed before any study specific tests or procedures are done Adult male and female patients ≥20 years at the time of inclusion in the study Ability to understand and follow study-related instructions  Histological diagnosis of primary refractory or relapsed aggressive B-cell non-Hodgkin lymphoma (B-NHL), confirmed by a biopsy of involved nodal or extranodal site. Patients with any of the following histologies can be included:  DLBCL not otherwise specified (NOS) T-cell/histiocyte-rich large B-cell lymphoma Primary cutaneous DLBCL, leg type Epstein-Barr virus (EBV)-positive DLBCL, NOS DLBCL associated with chronic inflammation Primary mediastinal (thymic) large B-cell lymphoma Refractory disease is defined as no complete remission to first line therapy. Relapsed disease is defined as complete remission to first line therapy followed by disease relapse. Subjects must have received adequate first line therapy including at a minimum: i) anti-CD20 monoclonal antibody unless Investigator determines that tumor is CD20 negative, and ii) an anthracycline containing chemotherapy Regimen Women of childbearing potential must have a negative pregnancy test result within 7 days prior to the first study drug Administration For women of childbearing potential: agreement to remain abstinent (refrain from heterosexual intercourse) or use contraceptive measures, and agreement to refrain from donating eggs For men: agreement to remain abstinent (refrain from heterosexual intercourse) or use contraceptive measures, and agreement to refrain from donating sperm  Exclusion Criteria:  Primary or secondary central nervous system (CNS) lymphoma at the time of recruitment Richter's transformation or prior chronic lymphocytic leukemia (CLL) Vaccination with a live vaccine within 4 weeks prior to Treatment Received polatuzumab vedotin as part of the first line therapy Ongoing treatment or study procedures within any other Investigational Medicinal Product (IMP) clinical trial with the exception of follow-up. In case of a preceding clinical trial, last application of the respective IMP(s) must have been done more than five elimination half-lives before start of study medication in this trial. History of severe allergic or anaphylactic reactions to human, humanized, chimeric, or murine monoclonal antibodies History of hypersensitivity to any of the study drugs or their ingredients or to drugs with similar structure Pregnancy or breastfeeding, or intending to become pregnant during the study or within 12 months after the last dose of study drug