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:  -