Heterogeneous Expression of Programmed Death Receptor-ligand 1 on Circulating Tumor Cells in Patients With Lung Cancer

Background Blockade of the programmed death receptor-1 (PD-1) pathway is effective against solid tumors including lung cancer. PD-ligand 1 (PD-L1) expression on tumor tissue serves as a predictive biomarker for the efficacy of PD-1 pathway blockade. Here, we evaluated the expression of PD-L1 on circulating tumor cells (CTCs) in patients with lung cancer. Materials and Methods Peripheral whole blood (3 mL) was collected from patients, and CTCs and PD-L1 expression were detected using a microcavity array (MCA) system. Immunohistochemistry for PD-L1 detection was also performed using matched tumor tissues. Results Sixty-seven patients with lung cancer were enrolled in the study between July 2015 and April 2016 at Wakayama Medical University Hospital. The characteristics of the patients were as follows: median age, 71 years (range, 39-86 years); male, 72%; stage II to III/IV, 14%/85%; non–small-cell lung cancer/small-cell lung cancer/other, 73%/21%/6%. CTCs were detected in 66 of 67 patients (median, 19; range, 0-115), and more than 5 CTCs were detected in 78% of patients. PD-L1-expressing CTCs were detected in 73% of patients, and the proportion score of PD-L1-expressing CTCs ranged from 3% to 100%, suggesting intra-patient heterogeneity of PD-L1 expression on CTCs. Tumor tissues were available from 27 patients and were immunostained for PD-L1, and no correlation was observed between tumor tissues and CTCs based on the proportion score ( R 2 = 0.0103). Conclusion PD-L1 expression was detectable on CTCs in patients with lung cancer, and intra-patient heterogeneity was observed. No correlation was observed between PD-L1 expression in tumor tissues and CTCs.