Association between serum level soluble programmed cell death ligand 1 and prognosis in patients with non‐small cell lung cancer treated with anti‐PD‐1 antibody

BACKGROUND: Programmed cell death ligand 1 (PD‐L1) is known to have soluble forms aside from its membrane‐bound forms. The aim of this study was to evaluate the predictive and prognostic values of serum soluble PD‐L1 (sPD‐L1) in patients with non‐small cell lung cancer (NSCLC) who were treated with anti‐PD‐1 antibody. METHODS: A total of 233 patients were enrolled in this study. We assessed the level of serum sPD‐L1 before anti‐PD‐1 antibody treatment (pembrolizumab or nivolumab) and evaluated the correlation with PD‐L1 expression on tumor cells, the response to anti‐PD‐1 antibody treatment, and patient outcome. RESULTS: The median serum sPD‐L1 concentration was 67.7 (range, 25 to 223) pg/mL. A weak correlation between serum sPD‐L1 and tumor PD‐L1 expression was observed. The disease control rate in the high sPD‐L1 group (≥90 pg/mL) was significantly lower than that in the low sPD‐L1 group (<90 pg/mL) (37% vs. 57%, P = 0.0158). The progression‐free survival (PFS) and overall survival (OS) in the high sPD‐L1 group were significantly shorter than those in the low sPD‐L1 group (median PFS, 57 days vs. 177 days, P = 0.011; median OS, 182 days vs. not reached, P < 0.001). The high level of serum sPD‐L1 was independently associated with a shorter PFS (hazard ratio [HR], 1.910; P = 0.061) and OS (HR, 2.073; P = 0.034) in multivariate analysis. CONCLUSIONS: The serum sPD‐L1 level, which was only weakly correlated with the tumor PD‐L1 expression level, was an independent predictive and prognostic biomarker for NSCLC patients receiving anti‐PD‐1 antibody. KEY POINTS: SIGNIFICANT FINDINGS OF THE STUDY: The disease control rate in the high sPD‐L1 group was significantly lower than that in the low sPD‐L1 group. The progression‐free survival (PFS) and overall survival (OS) in the high sPD‐L1 group were significantly shorter than those in the low sPD‐L1 group. The high level of serum sPD‐L1 was independently associated with a shorter PFS and OS in multivariate analysis. WHAT THIS STUDY ADDS: This study demonstrated that serum sPD‐L1 level was an independent predictive and prognostic biomarker for NSCLC patients receiving anti‐PD‐1 antibody.