Rituximab Plus Methotrexate With or Without Lenalidomide in Treating Patients With Newly Diagnosed Primary Central Nervous System Lymphoma

Inclusion Criteria:

1. Histologically confirmed Primary Central Nervous System (CNS) lymphoma
2. Age range 18-75 years old.
3. Eastern Cooperative Oncology Group performance status 0 to 3.
4. Previously untreated. Patients treated with steroid alone are eligible.
5. Patient's who are not planned to undergo consolidation with autologous hematopoieticstem cell transplantation（HSCT）.
6. Measurable disease was defined as at least ≥1.0cm in short-diameter by MRI.
7. Life expectancy of ≥ 3 months (in the opinion of the investigator).
8. Participants must be able to understand and be willing to sign a written informedconsent document.
9. Women of reproductive potential must agree to use highly effective methods of birthcontrol during the period of therapy and for 6 months after the last dose of the studydrug. Men who are sexually active must agree to use highly effective contraceptionduring the period of therapy and for 6 months after the last dose.
10. Women of childbearing potential must have a negative plasma pregnancy test upon studyentry.
11. Adequate renal function: Estimated glomerular filtration rate (GFR) or estimatedcreatinine clearance (CrCl) ≥ 50 mL/min;Serum creatinine ≤ 2 times the upper limit ofnormal.
12. Adequate liver functions: Transaminase (AST/ALT) < 3 X upper normal value & Bilirubin < 2 X upper normal value.
13. Adequate hematological function: hemoglobin ≥ 9 g/dL absolute neutrophil count (ANC) ≥ 1,500/μL and platelet count ≥ 75,000/μL.

Exclusion Criteria:

1. Patient with systemic, non-CNS lymphoma metastatic to the CNS.
2. Patient is concurrently using other approved or investigational antineoplastic agents.
3. Presence of active hepatitis B virus(HBV) infection (HBsAg positive and HBV-DNA≥ 104),hepatitis C virus(HCV) infection, acquired and congenital immunodeficiency diseasesinclude but not limited to HIV.
4. Patient is allergic to components of the study drug.
5. Patient has an active concurrent malignancy requiring active therapy.
6. Patient has significant abnormalities on screening electrocardiogram (EKG) and activeand significant cardiovascular disease such as uncontrolled or symptomaticarrhythmias, uncontrolled congestive heart failure, uncontrolled hypertension,valvular disease, pericarditis, or myocardial infarction within 6 months of screening.
7. Patient is known to have an uncontrolled active systemic infection.
8. Patient has a life-threatening illness, medical condition, or organ system dysfunctionthat, in the opinion of the investigator, could compromise the subject's safety or putthe study outcomes at undue risk.
9. Women who are pregnant or nursing (lactating), where pregnancy is defined as a stateof a female after conception until the termination of gestation, confirmed by apositive plasma human chorionic gonadotropin(hCG) laboratory test of > 5 mIU/mL.
10. The patient is unwell or unable to participate in all required study evaluations andprocedures.
11. Drug abuse, medical, psychological or social conditions which may interfering withsubjects' participation in the study or evaluation of the results.
12. Patients considered unsuitable to participate in the study by the researchers.