RecruitingDrug trialA Study of Selinexor in Combination With Temozolomide and Anti-PD-1 Antibody in Patients With Relapsed/Refractory Primary Central Nervous System LymphomaThis study is a prospective, single-arm, open label, Phase Ib/II clinical study to evaluate the safety and efficacy of selinexor in combination with temozolomide and anti-PD-1 monoclonal antibody in patients with relapsed/refractory primary central nervous system lymphoma(PCNSL). Phase Ib used a "3+3" dose-climbing design to confirm the safety, maximum-tolerated dose (MTD,if any) and recommended phaseII dose (RP2D) of selinexor in combination with fixed dose of temozolomide and anti-PD-1 monoclonal antibody for 6 cycles. Phase II was a comprehensive evaluation of efficacy and safety. Subjects who achieved complete remission or partial remission were treated with anti-PD-1 monoclonal antibody maintenance therapy until disease progression or recurrence, intolerance of toxicity, death, loss of follow-up, withdrawal of notification (whatever happened first).