Selinexor Combined With R-GemOx as Second-line Treatment in Patients With Diffuse Large B-cell Lymphoma

Inclusion Criteria: * Have pathologically confirmed CD20 positive de novo DLBCL or DLBCL transformed from previously diagnosed indolent lymphoma (e.g., follicular lymphoma) * HIV-seropositive * Age 18-75 years * ECOG PS≤2 * Positron emission tomography (PET) positive measurable disease with at least one node having the longest diameter (LDi)\>1.5cm or one extranodal lesion with LDi\>1cm (per the Lugano Criteria 2014) (Documentation to be provided) * Aspartate aminotransferase (AST) or alanine aminotransferase (ALT) ≤ 2.5 × Upper limit of normal value (ULN), or ≤ 5 in the presence of known lymphoma involving the liver × ULN; Total serum bilirubin ≤ 2 × ULN, or ≤ 5 when Gilbert syndrome or known lymphoma affects the liver × ULN; Creatinine clearance (CrCl) calculated according to Cockcroft Gault formula ≥ 30 mL/min; * Absolute neutrophil count (ANC)≥1.5×10\^9/L,or Platelet count≥75×10\^9/L(No platelet were transfused within 14 days before the treatment of the study drug),or Hemoglobin≥80g/L(No red blood cells were transfused within 14 days before the treatment of the study drug) * Written informed consent in accordance with federal, local, and institutional guidelines * Patients understanding the characteristics of the disease and voluntarily joins the study program for treatment and follow-up * No other serious diseases in conflict with this program * Investigator believe that subjects can benefit Exclusion Criteria: * Patients with known central nervous system involvement by lymphoma; * Patients with a history of autoimmune diseases or syndrome requiring systemic use of steroid, such as hypophysitis, pneumonia, colitis, hepatitis, nephritis, hyperthyroidism and hypothyroidism * Patients received systemic glucocorticoid (prednisone \>20mg/d) or any other immunosuppressive therapy within 7 days before the first administration,excluding nasal spray inhalation or other topical glucocorticoids; * Uncontrolled heart diseases, including unstable angina pectoris, acute myocardial infarction 6 months before randomization, congestive heart failure (NYHA), cardiac function grade greater than grade III or IV, or left ventricular ejection fraction\<50%; * Patients previously treated with selinexor; * History of severe allergic reactions (as determined by treating physician) attributed to the drugs being used in the study; * Patients undergoing organ transplantation; * Diagnosed as malignant tumor other than lymphoma or receiving treatment,excluding: 1. Malignant tumors that have received treatment for the purpose of cure and have not developed known active diseases for ≥ 5 years before enrollment 2. Basal cell carcinoma of the skin (excluding melanoma) with adequate treatment and no signs of disease 3. Cervical carcinoma in situ with adequate treatment and no signs of disease * Patients with grade 2 or more neurotoxicity occurred within two weeks before treatment; * Severe infection; * Drug abuse, medical psychological or social conditions that may interfere with the subject's participation in the study or the evaluation of the results of the study; * Any active, serious psychiatric, medical, or other conditions/situations which, in the treating physician's opinion, could compromise the patient's safety