Circulating tumor cells (CTCs) refer to cancer cells that have detached from a primary tumor and entered the bloodstream, where they can circulate throughout the body and potentially form secondary tumors in other organs. The study of CTCs is an important area of cancer research as they provide valuable information about the spread of cancer, cancer progression, and treatment resistance. By analyzing CTCs, researchers can gain insights into the biology of cancer metastasis, develop personalized treatment strategies, and monitor the efficacy of cancer therapies. Detection and characterization of CTCs are challenging due to their rarity in the bloodstream, heterogeneity, and dynamic nature. Various technologies, such as liquid biopsy techniques and microfluidic devices, are being developed to isolate and analyze CTCs for clinical applications. Overall, the study of CTCs holds promise for improving cancer diagnosis, prognosis, and treatment.