Primary central nervous system lymphoma (PCNSL) has a progressively increasing incidence and unique clinical behavior, but researchers know little about its molecular phenotype, which originates from a cell type not normally found in the central nervous system and occurs at an anatomical site with specific structural, biological, and immunologic features. Although PCNSL is one of the worst prognostic tumors among lymphomas, it is still a potentially curable brain tumor. In PCNSL, the main poor prognostic factors include age >60 years, physical status score >1, elevated LDH, elevated cerebrospinal fluid protein concentrations, and deep brain involvement. the IELSG study showed that adding high-dose cytarabine to high-dose methotrexate in patients with PCNSL aged <75 years significantly improved patient regression with tolerable toxicity.