The purpose of this study is to evaluate the safety and efficacy of nemtabrutinib (formerly ARQ 531) in participants with hematologic malignancies of chronic lymphocytic leukemia (CLL)/ small lymphocytic lymphoma (SLL), Richter's transformation, marginal zone lymphoma (MZL), mantle cell lymphoma (MCL), follicular lymphoma (FL), and Waldenström's macroglobulinemia (WM).
Has an Eastern Cooperative Oncology Group (ECOG) performance status of 0 to 2 within 7 days before C1D1 (the first dose of study treatment)
Has a life expectancy of at least 3 months, based on the investigator assessment
Has the ability to swallow and retain oral medication
Participants who are Hepatitis B surface antigen (HBsAg)-positive are eligible if they have received Hepatitis B virus (HBV) antiviral therapy for at least 4 weeks and have undetectable HBV viral load prior to randomization
Has active HBV/HCV infection (Part 1 and Part 2)
Has a history of malignancy ≤3 years before providing documented informed consent. Participants with basal cell carcinoma of skin, squamous cell carcinoma of skin, or carcinoma in situ (e.g., breast carcinoma, cervical cancer in situ) that have undergone potential curative therapy are not excluded. Participants with low-risk, early-stage prostate cancer (T1-T2a, Gleason score ≤6, and prostate-specific antigen <10 ng/mL) either treated with definitive intent or untreated in active surveillance with SD are not excluded
Has active central nervous system (CNS) disease
Has an active infection requiring systemic therapy