RecruitingDrug trialSelinexor in Combination With MTX+Ritu to Treat R/R CNSLThis is a single-arm and open-label study to explore X+MTX+Ritu (ATG-010, Methotrexate, Rituximab) regimen in Relapse refractory PCNSL patients. Approximately 30 patients will be enrolled in the study. In dose escalation phase, patients with Relapse refractory PCNSL will be treated with X+MTX+Ritu regimen and escalating doses of oral ATG-010 weekly in a 3+3 design. Then a phase 2 expansion at the recommended dose level based on phase 1b trial will be conducted to evaluate the efficacy, safety and tolerability.