Abstract
INTRODUCTION: PD-L1 (Programmed Cell Death Ligand 1) is currently the only recognised marker of response to immunotherapy with anti-PD-1 or anti-PD-L1 antibodies in patients with advanced non-small cell lung cancer (NSCLC). However, this marker is not perfect. Soluble PD-L1 (sPD-L1) may be a novel predictor of immunotherapy efficacy in NSCLC patients. MATERIAL AND METHODS: We enrolled 120 patients (median age 68 ± 6.81 years, 70 males and 50 females) with locally advanced (stage IIIB; 10 patients) or advanced (stage IV; 110 patients) NSCLC. PD-L1 expression in tumour cells was assessed by immunohistochemistry (IHC) in 117 (97.5%) patients. The soluble PD-L1 concentration in plasma samples was measured using enzyme-linked immunosorbent assay (ELISA). The response to immunotherapy, progression-free survival (PFS), and overall survival (OS), calculated from the start of immunotherapy, were assessed in 119 patients. RESULTS: Patients with disease control had significantly lower (p = 0.0006) concentrations of sPD-L1 in blood plasma than patients with progression during the first months of immunotherapy or chemoimmunotherapy Patients with ≥ 6 month progression-free survival had a significantly higher (p = 0.013) percentage of tumor cells with PD-L1 expression than patients with shorter PFS. Patients with ≥ 6 months OS had significantly lower (p = 0.0142) plasma sPD-L1 concentrations than those with shorter overall survival. The median PFS was significantly higher in patients with low sPD-L1 concentrations than in those with high concentrations of this protein (5.8 vs. 2.5 months, HR = 0.6021, p = 0.0156). Similarly, patients with low sPD-L1 levels had a significantly higher median overall survival than those with sPD-L1 levels above the median (16.5 vs. 7 months, HR = 0.5354, p = 0.0071). There was no significant correlation between the percentage of tumour cells expressing PD-L1 and the concentration of sPD-L1 in the blood plasma. CONCLUSION: High sPD-L1 concentration is a negative predictor of immunotherapy efficacy in patients with NSCLC. It is worthwhile to determine sPD-L1 concentration to predict the risk of resistance to anti-PD-1 or anti-PD-L1 antibodies with greater certainty.