• DOR [ Time Frame: 18 months ]
  Duration of time from first occurrence of CR or PR until the first date that disease progression is objectively documented
• DCR [ Time Frame: 18 months ]
  Proportion of patients who achieve CR, PR, or SD for a minimum of 4 weeks, following the first dose of study drug (i.e., CR+PR+SD)
• OS [ Time Frame: 18 months ]
  Duration of time from the first dose of study drug until death due to any cause
• PFS [ Time Frame: 18 months ]
  Duration of time from the first dose of study drug until progression or death due to any cause

• DOR [ Time Frame: 18 months ]
  To determine the duration of response (DOR)
• DCR [ Time Frame: 18 months ]
  To determine the disease control rate (DCR)
• OS [ Time Frame: 18 months ]
  To determine the median overall survival (OS)
• PFS [ Time Frame: 18 months ]
  To determine the median progression-free survival (PFS)

Inclusion Criteria:

1. The patient must provide informed consent form (ICF) prior to the first screening procedure.
2. Age ≥18 years.
3. ECOG performance status of ≤ 2.
4. Patients should have estimated life expectancy of >3 months at study entry.
5. Previously treated, pathologically confirmed de novo DLBCL, or DLBCL transformed from previously diagnosed indolent lymphoma (e.g., follicular lymphoma).
6. Patients must have received at least 2 but no more than 5 previous systemic regimens for the treatment of their de novo or transformed DLBCL.
7. Documented clinical or radiographic evidence of progressive DLBCL prior to dosing.
8. Patients must have measurable disease per the revised criteria for response assessment of lymphoma (Cheson, 2014). Lymph nodes should be considered abnormal if the long axis is > 1.5 cm, regardless of the short axis. If a lymph node has a long axis of 1.1 to 1.5 cm, it should only be considered abnormal if its short axis is > 1.0. Lymph nodes ≤ 1.0 by ≤ 1.0 will not be considered abnormal for relapse or PD.
9. Patients must not be eligible for high-dose chemotherapy with autologous stem cell transplantation rescue.

Exclusion Criteria:

1. Patients who are pregnant or lactating.
2. DLBCL with mucosa-associated lymphoid tissue (MALT) lymphoma, composite lymphoma (Hodgkin's lymphoma +NHL), or DLBCL transformed from diseases other than indolent NHL or Richter's.
3. Primary mediastinal (thymic) large B-cell lymphoma.
4. Known central nervous system lymphoma or meningeal involvement.
5. Patients whose most recent systemic anticancer therapy include radiation, chemotherapy, immunotherapy, radio-immunotherapy, or any other anticancer therapy other than glucocorticoids < 6 weeks prior to first dose of study drug.
6. Patients who have not recovered to Grade ≤ 1 clinically significant adverse events, or to their baseline, from their most recent systemic anti-DLBCL therapy.
7. Patients with active graft-versus-host disease after allogeneic stem cell transplantation. At least 4 months must have elapsed since completion of allogeneic stem cell transplantation.
8. Major surgery within 2 weeks of first dose of study treatment of ATG-010.
9. Any life-threatening illness, medical condition or organ system dysfunction which, in the Investigator's opinion, could compromise the patient's safety.

10. Unstable cardiovascular function:

    1. Symptomatic ischemia, or
    2. Uncontrolled clinically significant conduction abnormalities (i.e., ventricular tachycardia on anti-arrhythmia are excluded; First degree atrioventricular block or asymptomatic left anterior fascicular block /right bundle branch block will not be excluded), or
    3. Congestive heart failure of New York Heart Association Class ≥3, or
    4. Myocardial infarction within 3 months.
11. Uncontrolled (i.e., clinically unstable) infection requiring parenteral antibiotics, antivirals, or antifungals within 1 week prior to first dose; however, prophylactic use of these agents is acceptable even if parenteral.
12. Active hepatitis B virus or hepatitis C virus infection.
13. Known human immunodeficiency virus infection.
14. Patients unable to swallow tablets, patients with malabsorption syndrome, or any other gastrointestinal disease or gastrointestinal dysfunction that could interfere with absorption of study treatment of ATG-010.