Inclusion Criteria:  Age ≥ 18 years  All subjects must have histologically or pathologically confirmed diagnosis of their malignancy and/or measurable R/R disease, as follows:  Cohort 1 only: Refractory or relapsed acute leukemia defined as > 5% blasts in the bone marrow or reappearance of blasts in the peripheral blood Cohort 2 only: Previously treated, pathologically confirmed de novo DLBCL, or DLBCL transformed from previously indolent lymphoma (e.g., follicular lymphoma) with documented clinical or radiological evidence of progressive or persistent disease. At study entry, subjects must have measurable disease as per the revised criteria for response assessment of lymphoma. Cohort 3 only: Measurable MM based on IMWG (International Myeloma Working Group) guidelines  Patients must be refractory or must have progressed on, or following discontinuation of the most recent anti-cancer therapy, with the following considerations:  Cohort 1 only: Have failed or are ineligible for any approved standard of care therapies, including HSCT (Hematopoietic Stem Cell Transplantation) Cohort 2 only: Must have received at least 2 but no more than 5 previous systemic regimens for the treatment of their de novo or transformed DLBCL (i.e., transformed from a previously diagnosed indolent lymphoma [e.g., follicular lymphoma]) Cohort 3 only: Must have received at least 3 but no more than 6 prior anti-MM regimens including proteasome inhibitor (e.g., bortezomib or carfilzomib) and immunomodulatory drug (IMiD) (e.g., lenalidomide or pomalidomide) therapy.  Exclusion Criteria:  Subjects who meet any of the following criteria will not be enrolled in the study (all cohorts, unless otherwise indicated):  Certain disease subtypes or occurrences, as follows:  Cohort 1: acute promyelocytic leukemia (APL), chronic myeloid leukemia (CML) in blast crisis, isolated extramedullary relapse (iEMR). Cohort 2: Primary mediastinal B-cell lymphoma (PMBCL), DLBCL transformed from diseases other than indolent non-Hodgkin's Lymphoma (NHL) Cohort 3: Active plasma cell leukemia, myeloma with amyloidosis, systemic light chain amyloidosis White Blood Count (WBC) > 25,000/ µL (uncontrollable with cytoreductive therapy)  Known central nervous involvement, as follows:  Cohort 1: Clinically active central nervous system (CNS) leukemia. Previously controlled CNS leukemia is acceptable Cohort 2: Active CNS lymphoma or meningeal involvement Prior menin inhibitor therapy Known positive test for human immunodeficiency virus, hepatitis C, or hepatitis B surface antigen Subjects with a pre-existing disorder predisposing them to a serious or life-threatening infection (e.g., cystic fibrosis, congenital or acquired immunodeficiency, bleeding disorder, or cytopenias not related to acute leukemia, DLBCL, or MM) An active uncontrolled acute or chronic systemic fungal, bacterial, or viral infection