Abstract IA09: Beyond counting: Imaging flow cytometry-based detection of therapeutic molecular targets in circulating tumor cells
Authors: Tinhofer Ingeborg 
Published: September 2020

Abstract
Detection of circulating tumor cells (CTCs) has been established as a blood-based biomarker of poor prognosis in most types of epithelial cancer. The observation of increased CTC detection rates in patients with metastatic disease supported the hypothesis that CTCs might represent the precursor cells of distant metastases. Experimental proof for this hypothesis was provided by studies in experimental mouse models in which single metastasis-initiating cells within the total pool of CTCs could be causally linked to the formation of distant metastases. In addition, a potential of CTCs of reseeding at the primary site has been reported, suggesting that CTCs could also play a role in local tumor recurrence. Enumeration and molecular characterization of CTCs might thus be clinically exploited for improving the clinical management of epithelial cancers both in the locally advanced and recurrent/metastatic disease setting. Numerous studies reported on the presence of CTCs in peripheral blood samples of head and neck squamous cell carcinoma (HNSCC) patients. Significant associations with clinical high-risk parameters such as advanced stage, high tumor burden, nodal disease, and distant metastasis were reported. Accordingly, CTC detection was correlated with increased risk of local and/or distant recurrence, progression-free and overall survival. Current data in HNSCC are not yet robust enough for the implementation of CTC detection in clinical routine. In addition, the mere enumeration of CTCs has proven insufficiently informative to prompt widespread clinical adoption. There is accumulating evidence that more extended phenotyping of CTCs might be necessary for improving their diagnostic value. Indeed, despite the estimated daily shedding of millions of tumor cells from the bulk tumor tissue, only a small subpopulation of CTCs is able to reach and survive in the blood circulation and to contribute to the formation of distant metastasis. Identification of the true metastasis-inducing subclones within the bulk CTC population remains a challenge but is imperative in order to improve the diagnostic potential of CTCs. In addition, improved knowledge of the relevant biologic mechanisms endowing CTCs with the potential to emigrate from the primary site to blood circulation, to survive their journey, and to reseed at distant organs will support the development of novel antimetastatic therapies. Several technologies are currently available that allow multiparametric CTC phenotyping at the single-cell level. These platforms include imaging flow cytometry (IFC), by which multispectral images from a large number of cells acquired in suspension can be analyzed. By combining the features of flow cytometry and fluorescent microscopy, information on the cell morphology together with the extent of target protein expression and its subcellular localization can be collected. This provides a unique opportunity for statistical analysis of large populations, but also helps in avoiding artifacts. In the talk, the evidence of a prognostic role of CTCs in HNSCc will be summarized. Results from recent studies reporting on multiparametric CTC phenotyping at the single-cell level will be presented. Examples of CTC-based biomarkers that could be exploited for the optimization of current molecular treatment strategies in HNSCC will be discussed.
Citation Format: Ingeborg Tinhofer. Beyond counting: Imaging flow cytometry-based detection of therapeutic molecular targets in circulating tumor cells [abstract]. In: Proceedings of the AACR-AHNS Head and Neck Cancer Conference: Optimizing Survival and Quality of Life through Basic, Clinical, and Translational Research; 2019 Apr 29-30; Austin, TX. Philadelphia (PA): AACR; Clin Cancer Res 2020;26(12_Suppl_2):Abstract nr IA09.