Clinical applications and future perspectives of circulating tumor cells in solid tumors

Metastasis remains the leading cause of cancer-related mortality, despite notable advancements in cancer diagnosis and treatment. Circulating tumor cells (CTCs), malignant cells shed from primary or metastatic lesions into the bloodstream, have emerged as promising biomarkers with considerable potential across the cancer care continuum. Unlike disseminated tumor cells (DTCs), which reside in distant tissues and require invasive sampling, CTCs can be isolated through minimally invasive liquid biopsies, enabling real-time monitoring of disease progression, therapeutic response, and emergence of resistance. However, current CTC detection methods face limitations in sensitivity, particularly in early-stage disease where cell counts are low. Recent technological innovations, including microfluidic platforms, size-based filtration, and nanotechnology-enhanced assays, aim to improve both sensitivity and specificity, allowing for deeper molecular characterization. Beyond enumeration, CTCs offer insight into tumor heterogeneity, epithelial-to-mesenchymal transition (EMT), and resistance mechanisms, and may hold predictive value in therapy selection. While CTC phenotyping and genotyping have shown prognostic significance in various solid tumors, standardized clinical protocols for integrating CTC analysis into treatment decision-making remain under development. Future research is focused on elucidating the functional biology of CTCs, including their role in metastasis and tumor dormancy. Additionally, CTC-based biomarkers could guide precision oncology strategies, allowing for patient-specific therapies and longitudinal surveillance. As detection platforms mature and clinical validation progresses, CTCs are poised to become integral tools in personalized cancer management.