A Study Comparing BGB-3111 and Ibrutinib in Participants With Waldenström's Macroglobulinemia (WM)

Key Inclusion Criteria:

* Clinical and definitive histologic diagnosis of WM
* Measurable disease, requiring treatment
* Participants with no prior therapy for WM, must be considered inappropriate candidates for treatment with a standard chemoimmunotherapy regimen
* Age ≥ 18 years old
* Eastern Cooperative Oncology Group (ECOG) performance status of 0-2
* Adequate bone marrow function
* Adequate renal and hepatic function
* Electrocardiogram/multigated acquisition scan (ECHO/MUGA) demonstrating left ventricular ejection fraction (LVEF)≥ the lower limit of institutional normal
* Participants may be enrolled who relapse after autologous stem cell transplant if they are at least 3 months after transplant, and after allogeneic transplant if they are at least 6 months post-transplant.
* Females of childbearing potential must agree to use highly effective forms of birth control throughout the course of the study and at least up to 90 days after last dose of study drug. Males must have undergone sterilization- vasectomy, or utilize a barrier method
* Life expectancy of \> 4 months

Key Exclusion Criteria:

* Prior exposure to a BTK inhibitor
* Evidence of disease transformation at the time of study entry
* Corticosteroids given with antineoplastic intent within 7 days, or chemotherapy given with antineoplastic intent, targeted therapy, or radiation therapy within 3 weeks, or antibody-based therapy within 4 weeks of the start of study drug
* Major surgery within 4 weeks of study treatment
* Toxicity of ≥ Grade 2 from prior anticancer therapy
* History of other active malignancies within 2 years of study entry, with exception of (1) adequately treated in-situ carcinoma of cervix; (2) localized basal cell or squamous cell carcinoma of skin; (3) previous malignancy confined and treated locally with curative intent
* Currently active, clinically significant cardiovascular disease such as uncontrolled arrhythmia, congestive heart failure, any Class 3 or 4 cardiac disease within 6 months of screening
* QTcF prolongation (defined as a QTcF \> 480 msec)
* Active, clinically significant Electrocardiogram (ECG) abnormalities
* Unable to swallow capsules or disease significantly affecting gastrointestinal function such as malabsorption syndrome, resection of the stomach or small bowel, symptomatic inflammatory bowel disease, or partial or complete bowel obstruction
* Uncontrolled active systemic infection or recent infection requiring parenteral anti-microbial therapy
* Known human immunodeficiency virus (HIV), or active hepatitis B or hepatitis C
* Pregnant or lactating women
* Any life-threatening illness, medical condition, organ system dysfunction, need for profound anticoagulation, or bleeding disorder, which, in the investigator's opinion, could compromise the subject's safety
* Any medications which are strong or moderate cytochrome P450, family 3, subfamily A (CYP3A) inhibitors or strong CYP3A inducers

NOTE: Other protocol defined Inclusion/Exclusion criteria may apply.