GB5121 in Adult Patients With Relapsed/Refractory CNS Lymphoma

Inclusion Criteria: 1. Patients must have histologically/cytologically confirmed primary central nervous system lymphoma (PCNSL), primary vitreoretinal lymphoma (PVRL), or CNS-only involvement of a systemic B-cell lymphoma. 2. All patients must have relapsed/refractory disease and must have received all possible standard-of-care CNS-directed therapy treatment regimens or patients for which further standard-of-care treatment options are contraindicated or declined. 3. Patients must be able to tolerate gadolinium-enhanced magnetic resonance imaging (MRI) scans, or contrast-enhanced computed tomography (CT). 4. Patients with parenchymal lesions must have baseline imaging (gadolinium-enhanced MRI or if contraindicated, contrast-enhanced CT, of the brain) within 28 days prior to first study drug dose. For patients with leptomeningeal disease only, cerebrospinal fluid (CSF) cytology must document lymphoma cells and/or imaging findings consistent with leptomeningeal disease after informed consent and prior to first study dose (at the discretion of the Investigator). 5. Patients with parenchymal lesions must have measurable disease (disease that has at least one lesion on imaging ≥ 10 mm in the longest diameter) on imaging (gadolinium-enhanced MRI or if contraindicated, contrast-enhanced CT, of the brain) prior to first study dose. 6. Patients must be able to tolerate and consent for a lumbar puncture and/or have pre-existing placement of an Ommaya reservoir, unless clinically contraindicated. 7. Patients must have a performance status of 0, 1, or 2 on the Eastern Cooperative Oncology Group (ECOG) Performance Scale. 8. Demonstrate adequate bone marrow and organ function. Exclusion Criteria: 1. Patients are concurrently using other approved or investigational antineoplastic agents. 2. Patients have an active concurrent malignancy requiring active therapy. 3. Patients are allergic to components of the study drug. 4. Patients have a known bleeding diathesis (eg, von Willebrand's disease) or hemophilia. 5. Patients who require therapeutic anticoagulation, including dual antiplatelet agents. Patients who have received therapeutic anticoagulation, including dual antiplatelet agents, within 5 half-lives of the anticoagulant or 14 days, whichever is longer, prior to starting the study drug. Patients who require the use of antiplatelet agents should be discussed with the Sponsor's Medical Monitor. 6. Patients have significant abnormalities on screening electrocardiogram (ECG) and active and significant cardiovascular disease such as uncontrolled or symptomatic arrhythmias, congestive heart failure, uncontrolled hypertension, valvular disease, pericarditis, or myocardial infarction within 6 months of screening. 7. Patients with any of the following will be excluded: 1. A marked baseline prolongation of QT/QTc interval (eg, repeated demonstration of a QTc interval \> 480 ms \[CTCAE grade 2\]) using Frederica's QT correction formula. 2. A history of additional risk factors for Torsades de Pointes (eg, heart failure, hypokalemia, family history of long QT syndrome). 3. The use of concomitant medications that prolong the QT/QTc interval. 8. Patients are known to have a history of active or chronic infection with hepatitis C virus (HCV), hepatitis B virus (HBV), as determined by serologic tests. 9. Known history of infection with human immunodeficiency virus (HIV). 10. Patients are known to have an uncontrolled active infection. 11. Patients have a history of stroke or intracranial hemorrhage within 6 months prior to enrollment. 12. Patients have a life-threatening illness, medical condition, or organ system dysfunction that, in the opinion of the Investigator, could compromise the subject's safety or put the study outcomes at undue risk. 13. Women who are pregnant or nursing (lactating).