Intravenous BI 836826 in Combination With Ibrutinib in Relapsed/Refractory CLL Patients Who Have Been Pre-treated With at Least One Prior Line of Systemic Therapy, and Who Are Eligible for Treatment With Ibrutinib

Inclusion criteria: * Diagnosis of Chronic Lymphocytic Leukemia (CLL) established according to International Workshop Chronic Lymphocytic Leukemia (IWCLL) criteria. * Relapsed or refractory CLL pre-treated with at least one prior line of systemic therapy for CLL. * Indication for treatment consistent with IWCLL criteria, i.e. at least one of the following criteria should be met * Evidence of progressive marrow failure as manifested by the development of, or worsening of, anemia and/or thrombocytopenia. * Massive or progressive or symptomatic splenomegaly. * Massive nodes or progressive or symptomatic lymphadenopathy. * Progressive lymphocytosis in the absence of infection, with an increase in blood Absolute Lymphocyte Count (ALC) \>=50% over a 2-month period, or a lymphocyte doubling time (LDT) of \<6 months (as long as initial ALC was \>=30000/µl). * Autoimmune anemia and/or thrombocytopenia that is poorly responsive to corticosteroids or other standard therapy. * Constitutional symptoms, defined as any one or more of the following disease-related symptoms or signs: * unintentional weight loss of 10% or more within the previous 6 months * significant fatigue * fevers higher than 100.5°F or 38.0°C for \>=2 weeks without other evidence of infection * night sweats for \> 1 month without evidence of infection * Clinically quantifiable disease burden defined as at least one of the following: * either ALC \>10 000/µL, or * measurable lymphadenopathy * quantifiable bone marrow infiltration documented in a bone marrow biopsy during screening * Resolution of all clinically relevant acute non-hematologic toxic effects of any prior antitumor therapy resolved to Grade \<=1 * Baseline laboratory data as defined as: Hemoglobin (Hb): \>=8g/dL Absolute Neutrophil Count (ANC): \>=1000/µL Platelet (PLT): \>=25000/µL Glomerular Filtration Rate (GFR) or Creatinine Clearance: \>=30ml/min Aspartate Aminotransferase (AST) and Alanine Aminotransferase (ALT): \<3 x Upper Limit of Normal (ULN) Bilirubin - total: \<1.5 x ULN Activated Partial Thromboplastin Time (aPTT), Prothrombin Time (PT) or International Normalized Ratio (INR): \<=1.5 x ULN PT \<=1.5 x ULN, INR \<=1.5 * Male or female patients. Women of childbearing potential must agree to use highly effective methods of birth control during the trial and for at least 1 year after the last dose of BI 836826 and 1 month after the last dose of ibrutinib. * Eastern Cooperative Oncology Group (ECOG) performance score of 0 to 2. * Age 18 years and older * Eligible and able to secure sourcing for ibrutinib * Written Informed Consent * Further Inclusion criteria apply Exclusion criteria: * Known transformation of Chronic Lymphocytic Leukemia (CLL) to an aggressive B-cell malignancy at the time of screening * Prior allogeneic stem cell transplant within one year or active graft vs. host disease. * History of a non-CLL malignancy except for adequately treated in situ, stage 1 or 2 carcinoma in Complete Response (CR), or any other cancer that has been in CR for \>=2 years after end of cancer treatment. * Active, uncontrolled autoimmune cytopenia. Patients with autoimmune cytopenia which is controlled with corticosteroids at doses of \<=20 mg prednisolone or equivalent may be enrolled. * Previous CLL treatment with a CD37-targeting antibody or a CD37-antibody drug conjugate. * Previous treatment with ibrutinib * Previous treatment with another Bruton's Tyrosine Kinase (BTK) -inhibitor. * Ongoing systemic immunosuppressive therapy other than corticosteroids. * Active bacterial, viral, or fungal infection requiring systemic treatment at the time of study entry. * Human Immunodeficiency Virus (HIV) infection * Active hepatitis B or C as evidenced by detection of virus specific Deoxyribonucleic Acid (DNA) or Ribonucleic Acid (RNA). * History of stroke or intracranial hemorrhage within 6 months prior to enrollment * Chronic persistent atrial flutter or atrial fibrillation. Patients with intermittent atrial fibrillation may be enrolled if without episode for \>= 6 months and without indication for anti-coagulation * Requirement for chronic anticoagulation with warfarin or with direct oral anticoagulants at the time of screening. * Chronic treatment (i.e. \>7 days) with a strong Cytochrome P450 (CYP3A) inhibitor which cannot be terminated prior to the first dose of ibrutinib. * Unstable angina pectoris, uncontrolled hypertension, uncontrolled asthma or other pulmonary disease * Women who are pregnant, nursing, or who plan to become pregnant while in the trial * Further Exclusion criteria apply