Abstract 1359: Detection of PD-L1 positive circulating tumor cells from patient with bladder cancer

Immunotherapy with PD-L1 inhibitors greatly enhanced the clinical outcomes of patients with late stage metastatic bladder cancer. However, a concern has been raised in the front-line clinical use of PD-L1 inhibitors (permbrolizumab and atezolizumab) as a single treatment to PD-L1-low patients, due to a poorer overall survival compared with patients treated with plantinum-based chemotherapy. In accordance, reliable evaluation of PD-L1 expression is required for selecting patients relevant for treatment with PD-L1 inhibitors. However, due to the regional heterogeneity in primary tumor, evaluation of PD-L1 levels in tissue biopsy might be less reliable than the levels in circulating tumor cells (CTCs). Here, we developed the evaluating system of PD-L1 levels in CTCs isolated from the blood of patients with bladder cancer. Initially, CTCs were enriched by Smart Biopsy Cell Isolator (CytoGen), which utilizes the size-based gravity filtration for CTC isolation. The isolated CTCs were then validated with the expression of EpCAM, Vimentin and CK as well as a negative selection with CD45, and were analyzed for PD-L1 expression status by immunocytochemical staining. Using the evaluating system, we show that PD-L1 (+) cancer cell was efficiently recovered from the healthy human blood samples in a spike and recovery experiment. Furthermore, we evaluated PD-L1 expression status in CTCs isolated from ~25 patients with bladder cancer. Collectively, this study implicates the possibility that PD-L1 expression status could be analyzed at the levels of CTCs instead of the matching primary tumor tissue biopsy, probably with a better clinical diagnostic option.Citation Format: Yongjoon Suh, Seong-Kun Kim, Hye Seon Lee, Yun-Gyu Jeong, Jeong-Mi Moon, Myoung Shin Kim, Byung Hee Jeon, U-Syn Ha. Detection of PD-L1 positive circulating tumor cells from patient with bladder cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 1359.