Circulating Tumor Cells – An Overview of the Current Progress and Clinical Perspectives

Circulating tumor cells (CTCs) are cancerous cells that can detach from the primary tumor and circulate through the blood vessels until they reach a tissue or an organ and initiate metastasis. It is worth noting that in many types of cancer, the presence of CTCs in blood samples either independently or in clusters is considered a poor prognostic marker. This is because it indicates a lower overall survival (OS), a poorer progression-free survival (PFS), and a higher potential for metastasis. Characterising circulating tumor cells (CTCs) and monitoring their numbers can provide crucial information in managing cancer progression. Therefore, CTCs can be extremely useful in therapeutic monitoring, allowing doctors to follow treatment efficacy and make certain adjustments depending on their quantification. Research on CTCs as a liquid biopsy analyte has seen significant advancements, leading to the translational use of CTCs as potential biomarkers. However, low concentration and the lack of standardised detection methods make it challenging to detect CTCs. We offer an overview of the various phenotypic changes of CTCs and the epithelialmesenchymal transition (EMT) process that promotes the spread of cancerous cells. We also explore the biomarkers that characterise CTCs, as well as the primary isolation techniques. Finally, we highlight the clinical perspectives of CTCs and their relevance in monitoring cancer progression and response to treatment. Thus, we believe that the study of CTCs can provide a deeper understanding of the metastasis process, which could ultimately lead to improved patient outcomes.