Monitoring PD-L1 Expression on Circulating Tumor–Associated Cells in Recurrent Metastatic Non–Small-Cell Lung Carcinoma Predicts Response to Immunotherapy With Radiation Therapy

PURPOSE Current diagnostic methods to determine programmed death 1 (PD-1) receptor and its ligand (PD-L1)/PD-1 immunotherapy (immune checkpoint inhibitor [ICI]) efficacy in recurrent or metastatic non–small-cell lung carcinoma (rmNSCLC) are imprecise. Although previously shown that patients with high tumor PD-L1 (≥ 50%) demonstrate clinical benefit in the form of disease reduction and improved survival, patients with low PD-L1 (< 50%) sometimes benefit from treatment. Since the PD-L1/PD-1 pathway is dynamic, monitoring PD-L1 levels during treatment may be more accurate than a static baseline tumor biopsy; however, rebiopsying the primary or metastatic disease is rarely feasible. Liquid biopsies that measure the upregulation of PD-L1 on tumor-associated cells (TACs), ie, cancer-associated macrophage-like cells and circulating tumor cells, have been performed, but their predictive value for ICI therapy efficacy is unknown. MATERIALS AND METHODS We initiated a single-blind prospective study to evaluate TAC PD-L1 expression changes in rmNSCLC from blood samples before (T0) and after (T1) treatment with ICI (ICI, n = 41) or without ICI (no ICI, n = 41). Anonymized blood was filtered to isolate TACs, which were then quantified for high/low PD-L1 expression. Progression-free survival (PFS) or overall survival (OS) hazard ratios (HRs) were evaluated at 18 and 24 months by censored univariate analysis. RESULTS Increased TAC PD-L1 expression between T0 and T1 in patients who were not treated with ICI had no relationship with PFS or OS. However, increased TAC PD-L1 expression between T0 and T1 in patients treated with ICI had significantly better PFS (HR, 3.49; 95% CI, 1.5 to 8.3; P = .0091) and OS (HR, 3.058; 95% CI, 1.2 to 7.9; P = .0410). CONCLUSION Blood-based monitoring of dynamic changes in PD-L1 in TACs appears to identify patients with rmNSCLC who may benefit from ICI.