Primary central nervous system lymphoma (PCNSL) is a rare extranodal non-hodgkin's lymphoma confined to the central nervous system. It accounts for about 4% of all intracranial tumors and 4% to 6% of all non-Hodgkin's lymphomas . Among them, the most common type is diffuse large B cell lymphoma (DLBCL), accounting for about 95% of all cases. High dose methotrexate (HD-MTX) based chemotherapy can improve the prognosis of patients, but only 30% to 40% of patients can achieve sustained remission, and the overall prognosis is very poor[4, 6]. Currently, the International Extranodal Lymphoma Study Group (IESLG) prognostic scoring system and the Memorial Sloan Kettering Cancer Center (MSKCC) prognostic index are widely used to evaluate the prognosis in patients with PCNSL. However, IESLG model has some limitations such as the relatively small number of patients and short follow-up period. MSKCC model may have an inherent selection bias because retrospective data were collected from a single large institution. Therefore, there is a urgent need to identify novel indicators for prognosis evaluation and risk stratification in PCNSL patients.

Inclusion Criteria:

(i)The pathological biopsy and immunohistochemistry diagnosis were PCNSL according to WHO diagnostic criteria for PCNSL in 2016. (ii) No treatment has been received. (iii)There were no diseases with malignant tumor, serious infection, other blood system diseases, immune system diseases and other conditions which may have great influence on peripheral blood lymphocyte count. (iv) The clinical data were complete.

Exclusion Criteria:

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Clinical data of PCNSL patients were collected retrospectively, such as sex, age, physical state (ECOG score), cell source classification, number of lesions, whether the lesions involved deep structure, etc. The data of laboratory examination include the protein content in cerebrospinal fluid, lactate dehydrogenase (LDH), β2- macroglobulin (β2-MG), IESLG score, ALC and Ki-67.