 Circulating tumor cells, CTCs, are rare cancer cells that circulate in the blood after sloughing off from the primary tumor. Understanding their metastatic cascade has potential for identifying targets against cancer metastasis. Detecting CTCs is challenging due to their rarity, but emerging technologies have facilitated their clinical application. Molecular markers such as epithelial cell adhesion molecule are commonly used to detect CTCs, which have increased metastatic capacity due to properties associated with epithelial to mesenchymal transition and stem-ness. Only a small proportion of CTCs can survive and initiate metastases, suggesting an interaction between CTCs and the hostile blood microenvironment is essential for metastasis. Single-cell sequencing has revealed the genome and transcriptome of CTCs, and has clinical applications in monitoring response to cancer treatment and evaluating prognosis. Overall, CTCs provide significant insights into metastatic processes and will open new avenues for useful clinical applications. This article was authored by Ganfeng Lin, Les Anxion, Meng Luo, and others. We are article.tv, links in the description below.