Liquid biopsy enables repeated, minimally invasive assessments of tumor evolution and therapeutic responses. In addition to cfDNA, circulating tumor cells (CTCs) provide intact cellular material for capturing comprehensive genomic, transcriptomic, and proteomic features. Currently, the most established utility of CTCs is prognostic; in metastatic breast cancer, patients with ≥5 CTCs per 7.5 mL of blood exhibit significantly shorter OS (approximately 10 months vs. 18 months). While the use of CTCs to direct targeted therapies remains largely investigational, emerging evidence suggests that CTC characterization, including epithelial-mesenchymal transition and rare states detectable by single-cell RNA sequencing, reflects critical tumor heterogeneity and plasticity. Future progress will depend on reducing preanalytical variability, addressing platform-dependent capture bias, and establishing harmonized clinical thresholds. Integrating these refined CTC readouts with other liquid biopsy modalities is essential to enable clinically deployable multimodal strategies and optimize personalized treatment outcomes
Keywords: Circulating Tumor Cells; Biomarkers; Liquid Biopsy; Neoplasm Metastasis
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