CELL-FREE DNA & CIRCULATING TUMOR CELLS: THE CORE OF LIQUID BIOPSY IN CANCER

Liquid biopsy has emerged as a transformative, minimally invasive approach for cancer diagnosis, prognosis, and therapeutic monitoring. Among its key analytes, cell-free DNA (cfDNA) and circulating tumor cells (CTCs) represent the most informative biomarkers that reflect the molecular and cellular landscape of tumours in real time. cfDNA, including tumor-derived fragments known as circulating tumor DNA (ctDNA), provides valuable genetic and epigenetic insights into tumor heterogeneity, mutation profiling, and treatment resistance mechanisms. Conversely, CTCs offer cellular-level information, enabling phenotypic characterization, enumeration, and culture for functional assays. Together, cfDNA and CTCs form the core of the liquid biopsy concept, offering a comprehensive view of tumor dynamics through a simple blood draw. Recent technological advancements in next-generation sequencing, digital PCR, and microfluidic-based CTC isolation have significantly improved the sensitivity and specificity of these biomarkers. This review summarizes the biology, detection methodologies, and clinical relevance of cfDNA and CTCs, highlighting their synergistic role in early cancer detection, disease monitoring, and personalized therapy. The integration of cfDNA and CTC analyses holds promise for advancing precision oncology and transforming cancer management into a more predictive, preventive, and patient-centric paradigm.