The further aims of the study were to evaluate (1) the possible associations between plasma PD-1/PD-L1 levels and other laboratory and clinicopathological parameters, (2) whether baseline measurement of plasma PD-1/PD-L1 can indicate constant differences throughout the course of the disease between patients with high and low baseline plasma PD-1/PD-L1 levels, (3) how plasma PD-L1 and/or PD-1 affects mCRC survival, and (4) whether there is any association between tumor burden and plasma PD-L1 and/or PD-1 levels. This evidence concerns the gene PDCD1 and neoplasm.