R2-MTX With Lenalidomide Maintenance in Newly-diagnosed PCNSL：a Multicenter Phase Ib/II Stuty

This is a multicenter prospective single arm phase Ib/II study, and the purpose of this study is to evaluate the safety and efficiency of R2-MTX regimen (rituximab \& lenalidomide \& methotrexate) combined with lenalidomide maintenance in newly-diagnosed primary central nervous system lymphoma. 2-year Progression free survival (PFS) of the cohort is the primary endpoint.

There are 2 section of this trial. Step1 is a phase Ib study.The patients will be treated with R2-MTX regimen （Rituximab 375mg/m2 IV d0, methotrexate 3.5g/m2 civ d1, lenalidomide 15-25mg d1-14, 21 days per cycle) as induction regimen.The dose of rituximab and methotrexate is fixed dose. This is a 3+3 design Ib phase dose-escalation study to determined the maximum tolerated dose(MTD) of lenalidomide dose in combined regimen. 3 levels of lenalidomide dose will be investigated, 15mg, 20mg and 25mg. If the DLT is not found, the dose of 25mg qd will be used for phase II trial. \[update 02-Jun-2020：the recommended phase II doses is 25mg d1-14\] Step 2 is a single-arm phase 2 study with fixed does of R2-MTX regimen in newly-diagnosed PCNSL patients. The response will be evaluated every 2 cycles. Patients who achieved complete remission (CR) or partial remission (PR) will receive further treatment, and there are 6 cycles of R2-MTX regimen for the induction. The patients with stable disease (SD) or progressed disease (PD) will withdraw from the trial and receive salvage regimens. After total 6 induction cycles, the investigators evaluate the efficiency again, the patients with CR or PR will go to lenalidomide maintenance for 2 years or until progression of the disease (PD), unacceptable toxicity, or patient/investigator discretion. And the patients with SD or PD will receive salvage regimen. \[update 02-Jun-2020：Younger patients(≤60 years) who achieve PR after 6 cycles of induction therapy will be candidates of high-dose chemotherapy and stem cell rescue. Lenalidomide maintenance will be administed after the high-dose chemotherapy. Older patients(\>60 years) who achieve PR after 6 cycles of induction will go to lenalidomide maintenance directly.\] During following-up, surveillance examination and brain magnetic resonance imaging (MRI) scans can be performed every 3 months up to the first 2 years, followed by doctor visit every 6 months up to 5 years or the disease relapses.