Role of circulating tumor cells in breast cancer

Circulating tumor cells (CTCs) are tumor cells that shed from the primary tumor or metastatic loci, intravasate, and circulate in the bloodstream. CTCs have been suggested to play a major role in the metastatic spread of cancer, constantly shedding from tumors during proliferation or as a result of mechanical insults. Breast cancer (BC) is one of the most representative tumors in CTC research, with several studies conducted on its clinical validity and utility in both early and advanced BC (EBC and ABC, respectively). The assessment of the number and molecular profiles of CTCs is expected to provide a more tailored therapy for patients with BC. The detection of CTCs is usually dependent on molecular markers, and epithelial cell adhesion molecules are widely used. Although the CellSearch^® technology has been widely utilized for CTC detection, recent advances have led to the development of novel detection methods, facilitating further molecular analysis. In this review, we discuss the clinical applications of CTCs, current status of research, and efforts to incorporate CTC analysis into clinical practice. Additionally, we discuss potential challenges and future directions for integrating CTC analysis into clinical practice.