A Phase Ib Study of Oral Selinexor in Adult Patients With Relapsed/Refractory B-cell Lymphoma Receiving R-DHAOx or R-GDP

Inclusion Criteria: 1. Patients with any type of relapsed or refractory B-cell lymphoma 2. Eligible to receive R-DHAOx or R-GDP regarding the investigator's opinion 3. Who received prior therapy with at least one but no more than two lines therapies for B-Cell Lymphoma 4. Patient must have measurable disease defined by at least one single node or tumor lesion \> 1.5 cm 5. Aged between 18 years and 70 years (included) on date of consent signature 6. Eastern Cooperative Oncology Group (ECOG) performance status of 0, 1 or 2 7. With a life expectancy of ≥ 3 months 8. Having signed a written informed consent 9. Male patients (if sexually active with a woman of childbearing potential) must agree to use a reliable method of birth control during the study treatment and for at least 6 months after the last study drug administration. Male patients must agree to not donate sperm during the study treatment and for at least 6 months after the last study drug administration 10. Female patients of childbearing potential must agree to use two reliable methods of birth control during study treatment and for 6 months after the last dose and have a negative serum human chorionic gonadotropin (hCG) pregnancy test within 3 days prior to C1D1. Reliable methods of contraception include intrauterine devices, hormonal contraceptives \[contraceptive pills, implants, transdermal patches, hormonal vaginal devices or injections with prolonged release\], abstinence or sterilization of the partner. Exclusion Criteria: 1. Previous treatment with selinexor 2. Known central nervous system or meningeal involvement by lymphoma 3. Contraindication to any drug contained in these regimen 4. Subjects with known Human Immunodeficiency Virus (HIV) positivity 5. Subjects with known active Hepatitis B (HB) infection (positive Ag HBs) or positive serology to hepatitis B (Ag HBs or antibody anti-HB c or positive DNA PCR) or active Hepatitis C (HCV) infection (patients with positive HCV serology are eligible only if PCR is negative for known HCV RNA) 6. Subjects with any uncontrolled active systemic infection requiring intravenous (IV) antibiotics 7. Any of the following laboratory abnormalities within 14 days prior to first administration (C1D1) of study treatment: 1. Absolute neutrophil count (ANC) \< 1,000 cells/mm3 (1.0 x 109/L) 2. Spontaneous (within 7 days of any platelet transfusion) platelet count \< 100,000/mm3 (100 x 109/L) (75 x 109/L if due to lymphoma) 3. Aspartate aminotransferase (AST) or Alanine aminotransferase (ALT) \> 5.0 x upper limit of normal (ULN) 4. Serum total bilirubin \> 2x Upper Limit of Normal (ULN), or \> 5x ULN if due to Gilbert syndrome or lymphoma involvement 8. Creatinine clearance \< 50 mL /min (for patients who will receive DHAOx) or \< 70 mL/min (for GDP) 9. Subjects with pre-existing ≥ Grade 2 neuropathy 10. Prior history of malignancies other than lymphoma (except for basal cell or squamous cell carcinoma of the skin or in situ carcinoma of the cervix or breast) unless the subject has been free of the disease for ≥ 3 years 11. Any life-threatening illness, serious active disease or co-morbid medical condition, laboratory abnormality, organ system dysfunction or psychiatric illness which, in the investigator's opinion, could compromise the patient's safety, interfere with the absorption or metabolism of selinexor, or put the study outcomes at undue risk, or that would prevent the subject from signing the informed consent form 12. Pregnant or breastfeeding women 13. Use of any standard or experimental anti-cancer drug therapy within 28 days of the initiation (Day 1) of study drug therapy (administration of glucocorticoids should not exceed 1mg/kg/day in the 14 days prior to C1D1)