Soluble Isoforms of PD-1 and PD-L1 in Non-Small Cell Lung Cancer: Correlation with Tumor Stage, Longitudinal Analysis...

Background: Soluble immune checkpoint molecules, including soluble PD-1 (sPD-1) and soluble PD-L1 (sPD-L1), have emerged as potential minimally invasive biomarkers in non-small cell lung cancer (NSCLC). However, their diagnostic, kinetic, and prognostic significance across different disease settings remains unclear. This prospective study evaluated baseline levels, longitudinal fluctuations, and clinical associations of sPD-1 and sPD-L1 in early- and advanced-stage NSCLC. Methods: Three cohorts were prospectively enrolled: early-stage NSCLC patients undergoing curative surgery (n = 25), advanced-stage NSCLC patients receiving pembrolizumab-based immunotherapy (n = 55), and non-oncological controls (n = 16). Serum sPD-1 and sPD-L1 were measured by ELISA at baseline and at four months post-surgery (early stage) or six months post-treatment (advanced stage). Baseline comparisons, longitudinal changes, correlation with tumor PD-L1 expression (TPS), and associations with recurrence (early stage) or 6-month objective response (advanced stage) were assessed. Results: Baseline sPD-1 and sPD-L1 levels did not differ significantly among controls, early-stage, and advanced-stage cohorts. In early-stage patients, sPD-L1 increased post-operatively (p = 0.006) while sPD-1 decreased (p < 0.001). In advanced-stage disease, sPD-1 declined during immunotherapy (p < 0.001), whereas sPD-L1 remained unchanged (p = 0.37). Baseline levels and continuous percent changes were not predictive of most outcomes. However, a ≥20% postoperative increase in sPD-L1 was strongly associated with recurrence in early-stage NSCLC (OR = 10.29; 95% CI: 1.40-215.20; p = 0.019). No sPD-1/PD-L1 metric predicted response in advanced disease. Baseline sPD-L1 showed no correlation with tumor PD-L1 expression (ρ = -0.09, p = 0.53) in the advanced-stage cohort. Conclusions: sPD-1 and sPD-L1 demonstrate distinct kinetic patterns across NSCLC settings. A postoperative >20% surge in sPD-L1 may identify early-stage patients at elevated risk of recurrence, whereas soluble checkpoints were not predictive of treatment response in advanced disease. These findings support further investigation of soluble checkpoint dynamics as complementary biomarkers in NSCLC management in larger cohorts.