The average survival of untreated newly diagnosed PCNSL is 3 months. In recent years, with the continuous improvement of treatment as well as protocols, especially chemotherapeutic agents and strategies, the treatment outcome of PCNSL has improved significantly. There are some reports that the five-year survival rate of PCNSL after treatment has reached 30-40%. (A) Clinical stability and emergency treatment of PCNSL before the treatment plan: PCNSL often has rapid disease progression, often with rapid lesion enlargement during the diagnosis process, sometimes even affecting the implementation of the regular treatment plan. For rapidly enlarging tumor lesions whose occupying effects are difficult to eliminate in a short time and affect the subsequent treatment, craniotomy can be performed to reduce the intracranial pressure while obtaining a pathological diagnosis and creating conditions for radiotherapy. If the intracranial lesions are multiple, or located deep in surgically inaccessible areas, stereotactic (navigation) biopsy is feasible to clarify the histological type. Over 70% of PCNSL is highly sensitive to adrenocorticotropic hormones; however, tumor regression in response to hormones is transient and cannot be used as a first-line treatment option. Conversely, the use of hormones prior to the diagnosis of PCNSL, although reducing the tumor size, affects the confirmation rate of biopsy, and therefore the use of adrenocorticosteroids prior to pathological diagnosis is not currently advocated. （The overall efficiency of radiotherapy for PCNSL is 90%, and about 60% of patients can have their lesions completely disappeared after irradiation. The average survival rate of PCNSL patients treated with whole brain high dose radiation therapy (WBRT) alone is only 12-18 months. There is no clinical data to prove that increasing spinal cord irradiation improves survival in PCNSL with lesions confined to the skull, and therefore WBRT is mostly used. The incidence of neurological impairment in PCNSL treated with WBRT is much higher than that of other brain tumors, and this is a problem that should not be ignored in treatment. 2/3 of PCNSL patients treated with WBRT have varying degrees of delayed neurological deficits, especially cognitive deficits such as dementia. especially cognitive dysfunction, such as dementia and urinary incontinence. Although the use of low-dose WBRT can reduce the incidence of neurological damage, it can also lead to early tumor recurrence and shorten survival time. (iii) Chemotherapy alone Although low-dose WBRT is used as a consolidation measure of chemotherapy in most cases, it needs to be used with caution in some special patients, especially in elderly patients (>65 years old), because the high incidence of delayed neurological damage still cannot be avoided, and sometimes only chemotherapy alone regimens are adopted. Systemic combination chemotherapy with cyclophosphamide, adriamycin, vincristine, and prednisone (CHOP), which was effective in systemic NHLs in the past, was used only to obtain short-term survival and is now used sparingly. The first recommended chemotherapy regimen is still based on high-dose MTX alone or in combination with other NHL-sensitive drugs, or an immunochemotherapy regimen in combination with rituximab. 2009 Massachusetts General Hospital (MGH) reported satisfactory results using high-dose MTX therapy alone for patients older than 70 years, with a mean survival of 37 months. Other reports, including the combination of temozolomide (TMZ), have kept neurotoxic side effects within acceptable limits. To increase drug concentrations in the CNS, intrathecal MTX injections have been reported for PCNSL that invade the soft meninges or cortex, but there is no conclusive evidence for their effectiveness. In addition, some drugs that raise the blood-brain barrier, such as mannitol, have been applied and their effectiveness has been demonstrated in many reports. (iv) Combined chemoradiotherapy In order to improve the treatment effect of PCNSL while reducing the degree of neurotoxicity and neuroradiological damage, combined chemoradiotherapy is the most commonly used treatment strategy. Although there are various reports on the types of drugs, doses and radiation doses, the treatment principles are basically the same. The dose of MTX ranges from 1-8 g/m2 for 3-12 months, and other combination chemotherapeutic agents include vincristine, cytarabine, and procarbazine, etc. The dose of WBRT ranges from 23-45 Gy. The Radiation Therapy Oncology Group (RTOG) reported in 2002 that using a five-course high-dose MTX, vincristine, procarbazine (MPV), and a total dose of 45 Gy WBRT regimen, 36% of patients were in complete remission after chemotherapy, 94% were effective, and the mean tumor-free survival time reached 24 months with a mean survival time of 36.9 months. In contrast, the incidence of delayed neurotoxicity was 15%. The treatment effect was much better than the previous WBRT-only regimen. In 2008, the IELSG Collaborative Group reported the results of a randomized controlled clinical phase II study of MTX alone versus MTX in combination with cytarabine for PCNSL at the American Society of Hematology meeting, which demonstrated for the first time that the combination was better than MTX alone in improving disease remission and survival. MTX is an inhibitor of dihydrofolate reductase, an essential coenzyme required for purine and thymine synthesis. High-dose MTX chemotherapy can cause severe systemic toxic effects such as bone marrow suppression, mucosal inflammation, and nephrotoxicity, so monitoring of blood levels is advisable. Nephrotoxicity can be reduced by drinking large amounts of water and alkalinizing the urine. Folinic acid (formyltetrahydrofolate) is a folate antagonist of methotrexate, often used as an antidote to high-dose MTX chemotherapy to correct the toxic effects on normal cells, but does not antagonize the toxic effects of methotrexate on malignant cells. Because of its poor ability to penetrate the blood-brain barrier, folinic acid can significantly antagonize the toxic effects of methotrexate on bone marrow and mucosa, while rarely affecting the efficacy of methotrexate on CNS lymphoma. In recent years, immunochemotherapy regimens developed on the basis of chemotherapy have helped to improve tumor remission rates, and therefore have gradually become hot and may be one of the future directions to further improve the efficacy of PCNSL treatment. 2007 RTOG group again reported an R-MPV immunochemotherapy regimen with the addition of rituximab to chemotherapy, followed by the administration of 23.4 Gy for patients in complete remission and 45 Gy of WBRT for other patients, followed by two courses of high-dose cytarabine in a similar “sandwich” regimen, with an overall efficiency of 93%, complete remission after 78% immunochemotherapy, and two-year survival rates of 67% and 57% for patients in complete remission (CR) and non-CR, respectively, with varying degrees of improvement in patient behavior over two years. Behavior improved to varying degrees. (v) Stem cell transplantation Autologous stem cells, as one of the effective treatments for relapsed or high-risk systemic lymphoma, have been used in recent years mainly as a rescue option for PCNSL. 2007 Montemurro et al. reported a clinical phase II multicenter study of 23 patients in incomplete remission with conventional therapy using high-dose MTX induction, high-dose Bacitracin, thiotepa chemotherapy and Three of these patients died during treatment and three died from delayed radiation brain injury. The overall two-year survival rate was 48%, and the two-year survival rate for patients receiving transplantation was 61%. (vi) Resolution therapy For PCNSL cases that fail first-line chemotherapy and relapse, a resolution therapy regimen is required. Although there is no standardized rescue regimen, targeted therapeutic measures can be used for different types of cases. WBRT is aimed at cases that have failed chemotherapy alone, or relapsed after chemotherapy. For patients who are in remission after MTX chemotherapy but relapsed, MTX-based chemotherapy can be administered again. In older, or poorer general condition patients may be treated with tidiazomide alone or in combination with rituximab. For younger, or generally better patients, combination chemotherapy or high-dose chemotherapy combined with stem cell transplantation may be attempted.