P34.02 Detection of PD-L1 Expression and Its Clinical Significance in Circulating Tumor Cells From Patients With Non-Small-Cell Lung Cancer

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The expression of programmed cell death ligand 1(PD-L1) is related to the efficacy of immune checkpoint inhibitors on patients with non-small cell lung cancer (NSCLC), but its clinical tissue samples are difficult to obtain, and initial tumor tissue (TT) samples are difficult to reflect the spatial-temporal heterogeneity of the tumor due to treatment and disease progression. Liquid biopsy plays a crucial role in individualized and precise treatment of tumors. Therefore, we explored the feasibility of separating circulating tumor cells (CTCs) based on size and detecting PD-L1 expression on CTCs, with the goal of laying a foundation for real-time individualized immunotherapy. Peripheral blood specimens were sampled from 66 NSCLC patients, and analyzed prospectively, and CTCs were separated from them by membrane filtration based on size. For 59 patients with paired TT specimens, the expression of PD-L1 in their CTCs and TTs was determined using the immunohistochemistry (IHC) and immunocytochemistry (ICC) based on 28-8 antibody, respectively, and comparatively analyzed. The expression of PD-L1 in TTs was set as a gold standard for calculation of five indexes including sensitivity, specificity, consistency, positive predictive value (PPV), and negative predictive value (NPV), and the Cohen kappa coefficient for CTCs and paired tissues was calculated. In addition, the T-test, Chi-square test, and Mann-Whitney U test were all adopted to analyze the correlation of clinical pathological features and prognosis with PD-L1 expression. The sensitivity and specificity in detecting PD-L1 in CTCs of the 41 initial treated patients were 88.89 % and 73.91%, and PPV and NPV in detecting it were 72.73% and 89.47%, respectively. In addition, the consistency in detecting PD-L1 in CTCs and paired tissues was 89.47%, and the Cohen kappa coefficient was 0.613. The univariate analysis of survival showed that the progression-free survival time of initial treated patients with positive PD-L1 expression in CTCs or TTs was shorter than that of those with negative PD-L1 expression in CTCs or TTs (P>0.05), and the positive PD-L1 expression in CTCs or tissues had nothing to do with age, sex, smoking status, histological type, and stage (all P > 0.05). The CTC PD-L1 detection in peripheral blood in initial treated NSCLC patients is highly consistent with that in paired TTs, which confirms the feasibility of CTC PD-L1 detection in peripheral blood, and lays a certain foundation for exploring real-time and individualized immunotherapy molecular biomarkers based on peripheral blood in the future.