Inclusion Criteria:

   - No prior treatment for diffuse B-cell lymphoma (DLBCL)

   - Histologically-confirmed non-germinal center B-cell subtype DLBCL

   - Stage II (not candidates for local x-ray therapy), III, or IV disease by the Ann Arbor
   Classification

   - At least 1 measurable site of disease according to Revised Response Criteria for
   Malignant Lymphoma

   - Revised International Prognostic Index score of >=1

   - Eastern Cooperative Oncology Group performance status grade of 0, 1, or 2

   - Hematology and biochemical laboratory values within protocol-defined parameters prior
   to random assignment and at baseline

   - Left ventricular ejection fraction within institutional normal limits, as determined
   by echocardiography or multiple uptake gated acquisition (MUGA) scan

   - Agrees to protocol-defined use of effective contraception (for women, these
   restrictions apply for 12 months after the last dose of rituximab or 1 month after the
   last dose of study drug, whichever is later; for men, these restrictions apply for 12
   months after the last dose of rituximab or 3 months after the last dose of study drug,
   whichever is later)

   - Men must agree to not donate sperm during and after the study for 12 months after the
   last dose of rituximab or 3 months after the last dose of study drug, whichever is
   later

   - Women of childbearing potential must have a negative serum or urine pregnancy test at
   screening

Exclusion Criteria:

   - Major surgery within 4 weeks of random assignment

   - Known central nervous system or primary mediastinal lymphoma

   - Prior history of indolent lymphoma

   - Diagnosed or treated for malignancy other than DLBCL, except: malignancy treated with
   curative intent and with no known active disease present for >=3 years before random
   assignment; adequately treated non-melanoma skin cancer or lentigo maligna without
   evidence of disease; adequately treated carcinoma in situ without evidence of disease

   - History of stroke or intracranial hemorrhage within 6 months prior to random
   assignment

   - Requires anticoagulation with warfarin or equivalent vitamin K antagonists

   - Requires treatment with strong CYP3A inhibitors

   - Prior anthracycline use >=150 mg/m2

   - Clinically significant cardiovascular disease such as uncontrolled or symptomatic
   arrhythmias, congestive heart failure, or myocardial infarction within 6 months of
   screening, or any Class 3 (moderate) or Class 4 (severe) cardiac disease as defined by
   the New York Heart Association Functional Classification

   - Known history of human immunodeficiency virus or active hepatitis C virus or active
   hepatitis B virus infection or any uncontrolled active systemic infection requiring
   intravenous antibiotics

   - Women who are pregnant or breastfeeding

   - Any life-threatening illness, medical condition, or organ system dysfunction which, in
   the investigator's opinion, could compromise the patient's safety, interfere with the
   absorption or metabolism of ibrutinib capsules, or put the study outcomes at undue
   risk