PDCD1 and cancer: The plasma concentrations of soluble PD-L1 (sPD-L1), soluble PD-1 (sPD-1), and WFDC2 were measured using ELISA at four time points: healthy controls and cancer patients before ICI treatment (pre-ICI), after two cycles of anti-PD-1 therapy (after two cycles), and after four cycles (after four cycles).