Liquid biopsy is a set of minimally invasive techniques that analyze cancer related material circulating in body fluids, mainly blood. Instead of cutting out tumor tissue, clinicians examine fragments of DNA, whole cells or vesicles shed by tumors, which makes repeated sampling feasible and safer.

Three main components are studied. Circulating tumor DNA (ctDNA) consists of short DNA fragments from cancer cells that carry characteristic mutations or chromosomal changes. Circulating tumor cells (CTCs) are intact cells released from primary or metastatic sites into the bloodstream and can reveal morphology, protein markers and functional properties. Extracellular vesicles such as exosomes transport DNA, RNA and proteins that reflect the molecular state of the tumor and its microenvironment.

Liquid biopsy is being used to detect actionable mutations, guide targeted therapies, and monitor minimal residual disease and early relapse. Because blood can be drawn repeatedly, it allows real time tracking of tumor evolution and treatment resistance. High sensitivity assays can detect very low levels of ctDNA, although distinguishing tumor signals from normal background remains technically challenging.

Current research focuses on improving detection limits, standardizing protocols, and combining multiple biomarkers, for example integrating ctDNA with CTCs or exosomal RNA to increase accuracy. Applications extend beyond oncology to organ transplantation, prenatal testing and monitoring graft rejection or tissue injury by measuring cell free DNA patterns. Although not yet a full replacement for tissue biopsy, liquid biopsy is becoming an important complementary tool for precision medicine, enabling earlier intervention and more personalized treatment strategies.