Study of Lenalidomide/Rituximab Maintenance for Transplantation Ineligible Patients With PCNSL.

* After standard treatment of primary central nervous system lymphoma (PCNSL), high-dose methotrexate induction therapy, and consolidation therapy, most patients reach complete remission, but within the first 6 months, 35-60% of patients refractory to treatment or experience relapse during the first treatment. * The progression-free survival (PFS) period of relapsed patients is 2.2 months (0-29.6 months), and the survival period is reported as 3.5 months (0-29.6 months). After relapse, the majority of patients die within 2-4 months due to neurologic deterioration * Consolidation therapy after induction therapy includes whole-brain radiation therapy, high-dose chemotherapy followed by autologous hematopoietic stem cell transplantation (auto-SCT), and high-dose chemotherapy alone. * However, the median age of the inducing patient is 65 years, and more than half of the patients who are unable to transplant autologous hematopoietic stem cells (auto-SCT) after induction therapy account for more than half. * Therefore, we intend to conduct a study to evaluate the efficacy and safety of maintenance therapy for rituximab and lenalidomide as one of the consolidation therapies for patients with primary central nervous system lymphoma (PCNSL).