Circulating tumor cells (CTCs) are rare cells shed from primary and metastatic cancers and mixed with blood components, making their isolation and characterization challenging. CTCs are crucial for understanding metastasis and serve as biomarkers for non-invasive tumor genotype monitoring. Advances in CTC isolation technologies enable clinical applications like early cancer detection and treatment response prediction. CTCs are identified in the bloodstream and are thought to be viable metastatic precursors. Current CTC detection methods include nucleic acid-based approaches, physical property-based methods, and antibody-based capture. The CellSearch system and microfluidic CTC-chip are widely used, with the latter offering higher yield and purity. However, these methods have limitations in sensitivity and purity. CTCs have been shown to correlate with prognosis in breast, prostate, and colorectal cancers. Higher CTC counts are associated with poorer outcomes. CTCs can also be used to monitor treatment response, with decreases in CTC numbers indicating effective therapy. CTCs from localized cancers may shed before metastasis, suggesting their potential for early detection. Molecular characterization of CTCs reveals genetic and epigenetic changes, including aneuploidy, gene amplification, and mutations. These changes can indicate drug resistance and tumor evolution. CTCs can be analyzed for signaling pathways, proliferation, and apoptosis, providing insights into treatment response and metastatic potential. CTC clusters have been identified in cancer patients, suggesting they may contribute to metastasis. These clusters are more resistant to autolysis and may have protective effects against vascular shear stress. Further research is needed to understand their clinical significance. Future perspectives include the development of more sensitive and reliable CTC detection technologies, which could revolutionize cancer metastasis research and treatment. These technologies may enable non-invasive monitoring of tumor genotypes and the identification of metastatic precursor cells. As CTC research advances, it holds promise for improving cancer diagnosis, prognosis, and treatment strategies.Circulating tumor cells (CTCs) are rare cells shed from primary and metastatic cancers and mixed with blood components, making their isolation and characterization challenging. CTCs are crucial for understanding metastasis and serve as biomarkers for non-invasive tumor genotype monitoring. Advances in CTC isolation technologies enable clinical applications like early cancer detection and treatment response prediction. CTCs are identified in the bloodstream and are thought to be viable metastatic precursors. Current CTC detection methods include nucleic acid-based approaches, physical property-based methods, and antibody-based capture. The CellSearch system and microfluidic CTC-chip are widely used, with the latter offering higher yield and purity. However, these methods have limitations in sensitivity and purity. CTCs have been shown to correlate with prognosis in breast, prostate, and colorectal cancers. Higher CTC counts are associated with poorer outcomes. CTCs can also be used to monitor treatment response, with decreases in CTC numbers indicating effective therapy. CTCs from localized cancers may shed before metastasis, suggesting their potential for early detection. Molecular characterization of CTCs reveals genetic and epigenetic changes, including aneuploidy, gene amplification, and mutations. These changes can indicate drug resistance and tumor evolution. CTCs can be analyzed for signaling pathways, proliferation, and apoptosis, providing insights into treatment response and metastatic potential. CTC clusters have been identified in cancer patients, suggesting they may contribute to metastasis. These clusters are more resistant to autolysis and may have protective effects against vascular shear stress. Further research is needed to understand their clinical significance. Future perspectives include the development of more sensitive and reliable CTC detection technologies, which could revolutionize cancer metastasis research and treatment. These technologies may enable non-invasive monitoring of tumor genotypes and the identification of metastatic precursor cells. As CTC research advances, it holds promise for improving cancer diagnosis, prognosis, and treatment strategies.