Fig. 3. Liquid biopsy.

a CTCs, ctDNA, and cmiRNA are minor components of the blood, mixed with the normal erythrocytes, leucocytes, and cell-free nucleic acids. A minimally invasive venous blood collection has the potential to provide genetic information of all tumours within the body. b Plasma derived circulating nucleic acids (DNA, RNA, miRNA) are generally extracted using commercially available kits. Following extraction, ctDNA or cmiRNA can be detected by real time-qPCR, digital PCR or NGS, to detect the presence of disease, to detect mutations or SCNAs for diagnostic, prognostic, or genetic changes in response to therapy. c Circulating tumour cells are isolated from the blood by antibody directed methods such as immunomagnetic beads, or through their physical properties such as size and deformability. Once isolated, CTCs can be indirectly quantified using RT-PCR, or directly quantified using immunocytochemistry. Fluorescence in-situ hybridisation (FISH) can be used to detect SCNAs or changes to mRNA or miRNA expression. Single cell sequencing of CTCs can provide mutational and/or chromosomal copy number information.