The purpose of this study is to determine the efficacy and safety of the new treatment proposed in this study. Conducting a prospective study "CNS-2015" in patients with PDLBCL CNS made it possible to achieve 2-year EFS, DFS and OS of 83%, 83% and 88%, respectively. The presence of early relapses of the disease has now led to the need to find an alternative program for patients with PDLBCL CNS. In the new "CNS-2021" protocol, lenalidomide was included in the R-MPV program in order to intensify the induction stage. In the conditioning regimen, thiotepa was replaced by carmustine, due to its significant CNS bioavailability. In order to possibly prevent early relapses, an anti-PD-1 inhibitor (nivolumab) was used as maintenance therapy.

Patients will receive 4 cycles of RL-MPV (rituximab, methotrexate (MTX), procarbazine, vincristine, and lenalidomide (RL-MPV) as induction. The conditioning regimen prior to autologous blood stem cell transplantation includes high doses busulfan, thiotepa, and cyclophosphamide. After 3 months after autologous blood stem cell transplantation, maintenance therapy with nivolumab 3 mg/kg every 2 weeks for 6 months will be started.Patients will be out of the study at the time of death. All patients believe in the possibility of survival within 3 months throughout their lives. Survival status can be obtained by phone call, storage visit, or medical records (eg doctor's note/lab results from a clinic or storage visit).

Inclusion Criteria:

All patients must have non-Hodgkin's lymphoma involving the brain, as demonstrated by CT or MRI and histologic confirmation by one of the following: A positive CSF cytology for lymphoma or a monoclonal lymphocyte population as defined by cell surface markers.

A biopsy of the vitreous or uvea demonstrating non-Hodgkin's lymphoma. Brain biopsy.

Patients must be HIV-1 negative. Patient must have left ventricular ejection fraction ≥ 50%. Patients must have no evidence of systemic lymphoma. This must be demonstrated by a CT scan of the chest, abdomen and pelvis prior to registration.

Patients must have adequate bone marrow function (defined as peripheral leucocyte count >3000 cells/mm3 and platelet count > 100,000 cells/mm3), liver function (bilirubin < 2.0 mg/%), and adequate renal function (serum creatinine < 1.5 mg/dl or creatinine clearance > 50cc/min/1.73M2).

Men and women of reproductive potential must agree to use an acceptable method of birth control during treatment and for six months after completion of treatment.

Patients must be between 18 and 70years-old. Patients must sign an informed consent.

Exclusion Criteria:

Prior cranial irradiation Other active primary malignancy. Pre-existing immunodeficiency such as renal transplant recipient. Prior treatment with chemotherapy for CNS lymphoma.