In the present study, Siglec-15 was more frequently expressed on macrophages than on tumor cells, which was similar to the expression of PD-L1, although the co-expression of Siglec-15 and PD-L1 was detected on 30.0% of intratumoral macrophages and 21.8% of peritumoral macrophages in PCNSL tissues. This evidence concerns the gene CD274 and primary central nervous system lymphoma.