Figure 1.

The depiction of CTCs involves their detachment from the primary tumor, intravasation into the bloodstream, and subsequent circulation for the purpose of colonizing distant organs. Following extravasation, they establish secondary metastases. Fundamentally, the process involves circulating tumor cells undergoing epithelial-to-mesenchymal transition (EMT). During EMT, cancerous epithelial cells lose their cell-to-cell contact, adopting a more motile and less differentiated mesenchymal phenotype. CTCs can manifest either as single cells or as cell clusters, the latter exhibiting an enhanced metastatic potential. This diversity in CTC presentation captures a broader spectrum of clonal populations within a tumor, providing a comprehensive portrayal of tumor composition and its dynamic changes over time. Distinguishing themselves from other circulating cells in the blood, CTCs express specific EMT biomarkers, such as epithelial cell adhesion molecules (EpCAM) and cytokeratins (CKs).