Detection of Circulating Tumor Cells and Their Implications as a Biomarker for Diagnosis, Prognostication, and Therapeutic Monitoring in Hepatocellular Carcinoma

Abstract

Hepatocellular carcinoma (HCC) is among the leading causes of worldwide cancer-related morbidity and mortality. Poor prognosis of HCC is attributed primarily to tumor presentation at an advanced stage when there is no effective treatment to achieve the long term survival of patients. Currently available tests such as alpha-fetoprotein have limited accuracy as a diagnostic or prognostic biomarker for HCC. Liver biopsy provides tissue that can reveal tumor biology but it is not used routinely due to its invasiveness and risk of tumor seeding, especially in early-stage patients. Liver biopsy is also limited in revealing comprehensive tumor biology due to intratumoral heterogeneity. There is a clear need for new biomarkers to improve HCC detection, prognostication, prediction of treatment response, and disease monitoring with treatment. Liquid biopsy could be an effective method of early detection and management of HCC. Circulating tumor cells (CTCs) are cancer cells in circulation derived from the original tumor or metastatic foci, and their measurement by liquid biopsy represents a great potential in facilitating the implementation of precision medicine in patients with HCC. CTCs can be detected by a simple peripheral blood draw and potentially show global features of tumor characteristics. Various CTC detection platforms using immunoaffinity and biophysical properties have been developed to identify and capture CTCs with high efficiency. Quantitative abundance of CTCs, as well as biological characteristics and genomic heterogeneity among the CTCs, can predict disease prognosis and response to therapy in patients with HCC. This review article will discuss the currently available technologies for CTC detection and isolation, their utility in the clinical management of HCC patients, their limitations, and future directions of research.

Figure 1.

Circulating Tumor Cells in Hepatocellular Carcinoma HCC exhibits epithelial characteristics with surface expression of epithelial markers such as EpCAM and CK, as well as hepatocyte-specific markers such as ASGPR and GPC3. HCC cells enter the bloodstream to become CTCs in different ways - (1) maintaining the epithelial characteristic, (2) undergoing EMT with the expression of mesenchymal markers such as Twist and Vimentin, and (3) as CTC clusters consisting of multiple tumor cells as well as RBCs, platelets, stromal cells and fibroblasts. Upon entering the circulation, most CTCs get destroyed by anoikis, shear stress or immune attack. Some epithelial CTCs undergo EMT in transit. Eventually, CTCs that survive have acquired a more metastatic molecular profile with increased survival and decreased apoptosis. CTC clusters are protected from the processes that would kill isolated CTCs. Both the individual CTCs and CTC clusters that survive go on to metastasize and develop highly heterogeneous genetic, epigenetic and transcriptomic heterogeneity as well as polyploidy. The CTCs and CTC clusters can be collected and isolated from the peripheral blood via a variety of different enrichment techniques and can help with early detection, prognostication, and molecular characterization of HCC. Abbreviations: CTC, circulating tumor cells; EMT, epithelial to mesenchymal transition; HCC, hepatocellular carcinoma