Evaluation of PD-L1 expression on circulating tumor cells (CTCs) in patients with advanced urothelial carcinoma (UC)

Abstract

Immune checkpoint inhibition (ICI) of the PD-1/PD-L1 axis shows durable responses in a subset of patients with metastatic urothelial carcinoma (UC). However, PD-L1 expression in tumor biopsies does not necessarily correlate with response to PD-1/PD-L1 inhibitors. Thus, a reliable predictive biomarker is urgently needed. Here, the expression of PD-L1 on circulating tumor cells (CTCs) in blood from patients with advanced UC was analyzed. For this purpose, an assay to test PD-L1 expression on CTCs using the CellSearch® system was established using cells of five UC cell lines spiked into blood samples from healthy donors and applied to a heterogeneous cohort of UC patients. Enumeration of CTCs was performed in blood samples from 49 patients with advanced UC. PD-L1 expression in ≥1 CTC was found in 10 of 16 CTC-positive samples (63%). Both intra-and inter-patient heterogeneity regarding PD-L1 expression of CTCs were observed. Furthermore, vimentin-expressing CTCs were detected in 4 of 15 CTC-positive samples (27%), independently of PD-L1 analysis. Both CTC detection and presence of CTCs with moderate or strong PD-L1 expression correlated with worse overall survival. Analyses during disease course of three individual patients receiving ICI suggest that apart from CTC numbers also PD-L1 expression on CTCs might potentially indicate disease progression. This is the first study demonstrating the feasibility to detect CTC-PD-L1 expression in patients with advanced UC using the CellSearch® system. This assay is readily available for clinical application and could be implemented in future clinical trials to evaluate its relevance for predicting and monitoring response to ICI.

Microfluidic Assaying of Circulating Tumor Cells and Its Application in Risk Stratification of Urothelial Bladder Cancer

“…Nicolazzo et al (44) investigated the expression of survivin in the isolated CTCs and found that survivin expression was closed correlated with disease-free survival and cancer-specific survival in NMIBC patients. Similarly, a strong expression of PD-L1 in CTCs was reported to lead to a worse overall survival of patients with urothelial carcinoma (45). What's more, beyond the scope of CTCs, hemato-chemical biomarkers have also been explored in order for a more accurate risk stratification of bladder cancer.…”

Immune Checkpoint Inhibitors in Urothelial Carcinoma: Recommendations for Practical Approaches to PD-L1 and Other Potential Predictive Biomarker Testing

“…Preliminary findings suggest that it may be feasible to measure PD-L1 in circulating tumor cells (CTCs). However, these methods would not include PD-L1 expression on tumor-infiltrating ICs and the reproducibility and clinical utility of these assays remain to be proven [ 54 ].…”

Circulating Tumor Cells from Enumeration to Analysis: Current Challenges and Future Opportunities

“…The isolation and capture of CTCs based on biological characteristics of those heterogeneous cells utilize different biological markers expressed in the cells ( Table 2 ) [ 18 , 19 , 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 , 37 , 38 , 39 , 40 , 41 , 42 , 43 , 45 , 56 , 57 , 58 , 59 , 60 , 61 , 62 ]. The first data describing the detection and characterization of carcinoma cells in the systemic circulation (bone marrow) based on cytokeratin and MUC-1 glycoprotein expression in epithelial cancer cells, but not in healthy cells, were published 25 years ago [ 63 ].…”