In this study, we measured sPD-L1 from the archived serum samples of patients with PCNSL, and the median level in those patients (0.429 ng/mL, range: 0.324–0.757 ng/mL) was lower than the previously reported values in other hematologic malignancies such as DLBCL (1.84 ng/mL), extranodal NK/T-cell lymphoma (2.76 ng/mL), and multiple myeloma (4.15 ng/mL) [28, 31]. The gene discussed is SPDL1; the disease is primary central nervous system lymphoma.