RecruitingPhase 2Drug trialRituximab, Lenalidomide Combined With Methotrexate and Temozolomide For Primary Central Nervous System LymphomaThis is a prospective single arm, multi-center, phase II clinical trial to observe the efficacy and safety of Rituximab, Lenalidomide combined with high-dose Methotrexate and Temozolomide (RL-MT) in the first-line treatment for patients with primary central nervous system lymphoma.