Liquid biopsy is a minimally invasive method that uses blood or other body fluids to detect and monitor cancer. Instead of surgically sampling a tumor, clinicians analyze tumor derived material that circulates in the bloodstream, such as circulating tumor cells, circulating tumor DNA, cell free nucleic acids, exosomes and tumor educated platelets.

These components can reveal the presence of cancer, its molecular characteristics and how it changes over time. For example, fragment patterns and mutations in circulating tumor DNA can indicate specific tumor types, track tumor burden and identify emerging resistance to targeted therapies. Circulating tumor cells provide information about metastatic potential and can be analyzed for surface markers and gene expression. Exosomes and other extracellular vesicles carry proteins, RNA and DNA that reflect the biology of the originating tumor cells.

Liquid biopsy enables repeated sampling, which is particularly useful for monitoring disease progression, minimal residual disease and response to treatment in real time. It can detect molecular changes before they are visible on imaging and can capture heterogeneity better than a single tissue biopsy, since blood carries material from multiple tumor sites.

However, challenges remain. Tumor derived material is often rare and diluted within a background of normal components, so highly sensitive and specific technologies are required. Pre analytical variables, assay standardization and clinical validation are still being optimized. Despite these limitations, liquid biopsy is increasingly used in clinical practice for companion diagnostics, treatment selection and longitudinal follow up, and it is being studied for early cancer detection and screening across multiple tumor types.