Patterns of PD-L1 expression on circulating tumor cells in Japanese patients with advanced lung cancer.

e23036Background: Immune-checkpoint blockage with anti-PD-1 antibodies is effective against human malignancies including lung cancer. Although the expression of PD-L1 on tumor cells is expected as a predictive biomarker, detection of PD-L1 expression level on tissues remains challenging due to its dynamic and unstable expression. Here, we isolated circulating tumor cells (CTCs) and then evaluated the expression of PD-L1 on them in patients with advanced non-small cell lung cancer (NSCLC) and small cell lung cancer (SCLC). Methods: Immuno-staining for PD-L1 was established using NSCLC cell lines H820, H441, A549 and H23, spiked in the peripheral blood obtained from healthy donors. For clinical evaluation, 3 ml of peripheral whole blood was collected from 41 advanced lung cancer patients prior to the initiation of chemotherapy. Cells were captured and stained by using MCA system (Hitachi Chemical Co., Ltd). CTCs were defined as those positive for DAPI and cytokeratin (CK) and negative for CD45. Results: Cha...