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Increased tumor-associated macrophages (TAMs) have been reported to be associated with poor prognosis in various tumors; however, the importance of TAMs in primary central nervous system lymphoma (PCNSL) has not been clarified. In 47 patients with PCNSL who were treated with high-dose methotrexate (MTX) and radiotherapy, the relationships between the infiltration levels of TAMs and the clinicopathological parameters were analyzed. Univariate analysis of the Cox proportional hazards model using continuous scales revealed that increased CD68 positive (+) TAMs was significantly associated with inferior progression-free survival (PFS) (P = 0.04), and trends were observed for the increased CD163+ TAMs and having shorter PFS (P = 0.05). However, increased TAMs were not associated with overall survival. Because TAMs are known to produce various cytokines, we examined the relationships between cerebrospinal fluid (CSF) cytokines and TAMs. CSF interleukin-6 (IL-6) and soluble IL-2 receptor were not correlated with the infiltration rate of TAMs; however, CSF IL-10 level was correlated with infiltration levels of CD68 and CD163+ TAMs. We also confirmed the expression of IL-10 in CD68+ and CD163+ TAMs by double immunostaining analysis. Our results indicate that a high level of IL-10 in CSF may be positively associated with the infiltration level of TAMs in PCNSLs.