The purpose of this study is to characterize the safety, tolerability, pharmacokinetics, pharmacodynamics, and preliminary antitumor activity of EXS73565 administered orally as a single agent in participants with relapsed/refractory B-cell malignancies.

Key Inclusion Criteria:

• Age ≥18 years at the time of signing the informed consent.
• Eastern Cooperative Oncology Group (ECOG) performance status of 0-1.
• Histologically confirmed diagnosis of one of the following B-cell malignancies: chronic lymphocytic leukemia (CLL), including Richter's transformation from CLL, mantle-cell lymphoma, diffuse large B-cell lymphoma, follicular lymphoma, marginal zone lymphoma, or waldenström macroglobulinaemia.
• Participants that have relapsed after standard of care or have progressed during standard of care or are not suitable for standard of care therapy

Key Exclusion Criteria:

• Any medical or psychiatric condition that, in the view of the Principal Investigator, could jeopardize or would compromise the participant's safety or ability to participate in the study.
• Known central nervous system (CNS) malignancy or primary CNS lymphoma.
• Concurrent active or previous malignancy (other than the primary lymphoma/CLL for which the participant will be treated on this protocol within 5 years prior to randomization; participants with prior cancers may be enrolled with documented Sponsor approval.
• Received anticancer therapy, including chemotherapy, immunotherapy, radiation therapy (with the exception of palliative radiotherapy), biologic therapy, cancer-related hormonal therapy, or any investigational therapy within 14 days or 5 half-lives (whichever is shorter) before the first dose of the study treatment.