Inclusion Criteria:

          -  Participant must be ≥ 18 years of age at the time of signing the informed consent.

          -  Participants with histologically confirmed, relapsed or refractory DLBCL, and where in
             the opinion of the investigator, a clinical trial is the best option for next
             treatment based on response and/or tolerability to prior lines of therapy. PART A

               -  Diagnosis must be confirmed by biopsy and be immunohistologically characterized.

               -  Tumour tissue must also be available for sending to AstraZeneca for central cell
                  of origin/pathology testing. PART B

               -  Must have received standard of care first line therapy.

               -  Diagnosis must be confirmed by biopsy and be immunohistologically characterised.

               -  A newly obtained tumour biopsy is mandatory at screening to confirm cell of
                  origin status and determine DLBCL subtype.

          -  Presence of radiographically measurable lymphadenopathy or extranodal lymphoid
             malignancy.

          -  Participants must have failed at least 2 prior therapies for the treatment of current
             disease, are not eligible for curative treatment options, and have no standard therapy
             available.

          -  Adequate haematologic function, without transfusion and growth factor support for

             ≥ 14 days before screening.

          -  Optional tumour biopsy on study: Participants are also encouraged to consent to and
             undergo an optional tumour biopsy at disease progression to support correlative
             biomarker studies.

          -  All participants must be willing and able to provide mandatory baseline bone marrow
             biopsy/aspirate.

        Exclusion Criteria:

          -  Treatment with prior Bruton's tyrosine kinase inhibitor.

          -  Current refractory nausea and vomiting, malabsorption syndrome, disease significantly
             affecting gastrointestinal function, resection of the stomach, extensive small bowel
             resection that is likely to affect absorption, symptomatic inflammatory bowel disease,
             partial or complete bowel obstruction, or gastric restrictions and bariatric surgery,
             such as gastric bypass.

          -  Prior use of standard anti-lymphoma therapy or radiation therapy within 14 days of
             receiving the first dose of study treatment.

          -  Requires treatment with strong CYP3A inhibitors or inducers.

          -  Requires treatment with proton-pump inhibitors. Participants receiving proton-pump
             inhibitors who switch to H2-receptor antagonists or antacids are eligible for
             enrolment to this study.

          -  Serologic status reflecting active hepatitis B or C infection.

          -  Active Cytomegalovirus (CMV) infection.

          -  Receipt of live, attenuated vaccine within 28 days before the first dose of study
             treatment (s).

          -  Requires or receiving therapeutic anticoagulants, with the exception of short-acting
             heparins, within 7 days of first dose of study treatment.

          -  Participants on dual antiplatelet and therapeutic anticoagulant therapy.