Evaluating the Effectiveness of Decitabine With Gemcitabine, Oxaliplatin for Relapsed/Refractory Peripheral T-cell Lymphoma

Inclusion Criteria: * Patients must meet all of the following criteria to be considered eligible. 1. Patients with histologically confirmed peripheral T-cell lymphoma (PTCL) who have either relapsed after first-line chemotherapy or experienced disease progression due to refractory disease, and who are deemed eligible for further chemotherapy. 2. Age ≥ 19 years. 3. Eastern Cooperative Oncology Group (ECOG) performance status ≤ 2. 4. Adequate bone marrow function, defined as: 1. White blood cell count ≥ 3,000/μL 2. Absolute neutrophil count ≥ 2,000/μL 3. Platelet count ≥ 75,000/μL 4. Hemoglobin ≥ 8.0 g/dL Note: Transfusions within 1 week prior to screening are not permitted. 5. Adequate renal function, defined as serum creatinine ≤ 1.5 × upper limit of normal (ULN). 6. Adequate hepatic function, defined as: 1. Serum total bilirubin ≤ 1.5 × ULN 2. AST (SGOT) and ALT (SGPT) ≤ 2.5 × ULN (or ≤ 5 × ULN in the presence of liver metastases) Note: Patients with hepatic dysfunction due to underlying disease may be enrolled at the investigator's discretion. 7. Presence of measurable disease. 8. Ability to understand and provide written informed consent. 9. Willingness and ability to comply with scheduled visits, treatment plans, laboratory tests, and other study procedures. 10. Female patients of childbearing potential must have a negative serum or urine human chorionic gonadotropin (hCG) test within 3 weeks prior to treatment, and must agree to use effective contraception (e.g., barrier methods) from 4 weeks prior to treatment initiation through the study duration. Exclusion Criteria: * Patients will be deemed ineligible if they meet any of the exclusion criteria listed below. 1. Diagnosis of a malignancy other than lymphoma within the past 3 years. 2. More than two prior lines of chemotherapy for lymphoma. Note: Autologous stem cell transplantation is considered part of one treatment regimen. 3. Evidence of uncontrolled central nervous system involvement. 4. History of solid organ or allogeneic stem cell transplantation. 5. Uncontrolled seizures or significant psychiatric disorders. 6. Pregnancy or breastfeeding. 7. Any other serious illness or medical condition deemed inappropriate by the investigator. 8. Presence of grade ≥2 peripheral neuropathy. 9. Prior treatment with gemcitabine for lymphoma. 10. History of HIV infection or active, uncontrolled bacterial, viral, or fungal infections. 11. Surgery within 14 days prior to enrollment, or failure to recover from surgical complications. 12. Patients currently receiving thoracic radiotherapy.