Circulating tumor cells PD-L1 expression detection and correlation of therapeutic efficacy of immune checkpoint inhibition in advanced non-small-cell lung cancer

Introduction: This study investigated whether programmed death-ligand 1 (PD-L1) expression of circulating tumor cells (CTCs) in peripheral blood can serve as a predictive biomarker for immunotherapy efficacy in patients with advanced non-small-cell lung cancer (NSCLC).Methods: We employed a negative enrichment method to isolate CTCs. We identified PD L1 + CTCs as PD-L1+/4 ' ,6-diamidino-2-phenylindole (DAPI)+/CD45-circulating tumor cells through an immunofluorescence method. Tumor tissue PD-L1 expression was determined by immunohistochemical staining. The correlation between CTC PD-L1 expression and patients' prognostic features was estimated through the Kaplan-Meier method.Results: CTCs released a higher detection rate of PD-L1 expression than tumor tissues (53.0% vs. 42.1%). No correlation was observed between them. Forty-nine NSCLC patients received anti-PD-1/PD-L1 immunotherapy (three with combined anti-PD-1/PD-L1 and cytotoxic T lymphocyte-associated antigen-4 (CTLA-4), two with four cycles of combined immune checkpoint inhibitors [ICIs] plus chemotherapy and ICI monotherapy for maintenance). Patients with PD-L1 expression on tissue or CTCs had a median progression-free survival (mPFS) of 5.6 months (n = 36, 95% confidence interval [CI] 3.6-7.5 months), significantly longer than those without PD-L1 detection (n = 9, mPFS of 1.4 months, 95% CI 1.3-1.5 months, log-rank p = 0.032). The multivariable Cox proportional-hazard model suggested that the tissue or CTC PD-L1 expression was associated with a lower risk of progression (hazard ratio 0.45, 95% CI 0.21-0.98, p = 0.043).Conclusions: CTCs and tumor tissues reveal heterogeneous expression of PD-L1 in NSCLC patients. Patients with baseline PD-L1 expression on CTCs or tissue showed prolonged mPFS and may help to identify the subsets of patients who potentially benefit from immunotherapy.