SPDL1 and neoplasm: Considering the discrepancy of serum sPD-L1 with tumor tissue PD-L1 in terms of the association with survival, further study with larger study population should be performed to evaluate whether the measurement of sPD-L1 in serum could be a feasible and reproducible test for predicting the prognosis of PCNSL as well as the status of tissue PD-L1 expression.