A liquid biopsy, also known as fluid biopsy or fluid phase biopsy, is the sampling and analysis of non-solid biological tissue, primarily blood. Like traditional biopsy, this type of technique is mainly used as a diagnostic and monitoring tool for diseases such as cancer, with the added benefit of being largely non-invasive. Liquid biopsies may also be used to validate the efficiency of a cancer treatment drug by taking multiple samples in the span of a few weeks. The technology may also prove beneficial for patients after treatment to monitor relapse.
The clinical implementation of liquid biopsies is not yet widespread but is becoming standard of care in some areas.
Liquid biopsy refers to the molecular analysis in biological fluids of nucleic acids, subcellular structures, especially exosomes, and, in the context of cancer, circulating tumor cells.
Types There are several types of liquid biopsy methods; method selection depends on the condition that is being studied.
Disease Tissue sampled Sampling procedure Invasiveness Substance isolated Isolation and detection method Analysis RefsCancer (various) Blood Phlebotomy Minimally invasive Circulating tumor cells (CTCs) Various (e.g. CellSearch, RosetteStep, Dynabeads) Flow cytometry, nucleic acid extraction, immunocytochemistry, functional assays Cancer (various) Blood Phlebotomy Minimally invasive Circulating tumor DNA (ctDNA) DNA extraction Next-generation sequencing Urothelial carcinoma Urine Urine collection Non-invasive Urinary tumor DNA (utDNA) DNA extraction Next-generation sequencing Non-urological cancers Urine Urine collection Non-invasive Urine proteins, metabolites HPLC-MS Proteomics, metabolomics Bladder and prostate cancerUrineUrine collectionNon-invasiveExfoliated cancer cellsUrinalysisFluorescence in situ hybridizationHeart attack Blood Phlebotomy Minimally invasive Circulating endothelial cells (CECs) Various (e.g. CellSearch, HD-CEC) Flow cytometry Neurological diseases / brain tumors Cerebrospinal fluid Lumbar puncture Minimally invasive CSF proteins, nucleic acids Various ELISA, multiplex assay, next-generation sequencing Prenatal diagnosis Blood (maternal) Phlebotomy Minimally invasive Cell-free fetal DNA (cffDNA) DNA extraction Karyotyping, fluorescent in situ hybridization Prenatal diagnosis Blood (maternal) Phlebotomy Minimally invasive Fetal cells in maternal blood (FCMB) Flow cytometry Karyotyping, fluorescent in situ hybridization Prenatal diagnosis Blood (umbilical cord) Cordocentesis Invasive Umbilical blood cells and molecules Various Karyotyping, blood typing, blood tests, Kleihauer–Betke test, flow cytometry Prenatal diagnosis Amniotic fluid Amniocentesis Invasive Amniotic fluid cells and molecules Various Karyotyping, blood typing, L/S ratio, S/A ratio
A wide variety of biomarkers may be studied to detect or monitor other diseases. For example, isolation of protoporphyrin IX from blood samples can be used as a diagnostic tool for atherosclerosis. Cancer biomarkers in the blood include PSA (prostate cancer), CA19-9 (pancreatic cancer) and CA-125 (ovarian cancer).
Mechanism
Circulating tumor DNA (ctDNA) refers to DNA released by cancerous cells into the blood stream."What is circulating tumor DNA and how is it used to diagnose and manage cancer? ". National Institutes of Health Genetics Home Reference. 5 March 2019. Retrieved 12 March 2019. Cancer mutations in ctDNA mirror those found in traditional tumor biopsies, which allows them to be used as molecular biomarkers to track the disease."Liquid Biopsies Show High Correlation with Tissue Biopsy for Genetic Mutations" . Oncology Practice Management. July 2016. Retrieved 12 March 2019."Cell-free DNA as a biomarker in cancer". Extracell Vesicles Circ Nucleic Acid. Aug 2022. Retrieved 04 Aug 2022. These tests can have sensitive limits of detection, allowing monitoring of minimal residual disease after treatment. Scientists can purify and analyze ctDNA using next-generation sequencing (NGS) or PCR-based methods such as digital PCR.Picher, Andy."Liquid Biopsy, Key for Precision Medicine". Genetic Engineering & Biotechnology News. 23 July 2018. Retrieved 12 March 2019. NGS-based methods provide a comprehensive view of a cancer's genetic makeup and is especially useful in diagnosis while digital PCR offers a more targeted approach especially well-suited for detecting minimal residual disease and for monitoring treatment response and disease progression."Liquid Biopsy: Differences Among Technologies" . OncLive. 17 September 2017. Retrieved 12 March 2019.Ellis, Jen."dPCR: The Emergence of the Digital Age". Biocompare. 7 May 2018. Retrieved 12 March 2019. Recent progress in epigenetics has expanded the use of liquid biopsy for the detection of early-stage cancers, including by approaches such as Cancer Likelihood in Plasma (CLiP) .
Liquid biopsies can detect changes in tumor burden months or years before conventional imaging tests can, making them suitable for early tumor detection, monitoring, and detection of resistance mutations.McDowell, Sandy."Liquid Biopsies: Past, Present, and Future". American Cancer Society. 12 February 2018. Retrieved 12 March 2019."Liquid Biopsy: Using DNA in Blood to Detect, Track, and Treat Cancer". National Cancer Institute. 8 November 2017. Retrieved 12 March 2019. The increase in the adoption of NGS in various research fields, advancement in NGS, and increase in the adoption of personalized medicine are expected to drive growth in the global liquid biopsy market.
Clinical application
In cancer, liquid biopsy can be used for either multi-cancer screening tests, when solid tumor biopsies are not possible, to compare different treatments as part of clinical trials, to inform decisions for doctors/patients on which precision medicine treatment to select, and for minimal residual disease detection (disease monitoring). Liquid biopsy of circulating tumor DNA for EGFR-mutated lung cancer is approved by the FDA.
The CellSearch method for enumeration of circulating tumor cells in metastatic breast, metastatic colon, and metastatic prostate cancer has been validated and approved by the FDA as a useful prognostic method.
See also Radiographic imaging Cancer screening#Blood tests Circulating free DNA
External links NucPosDB: a database of nucleosome positioning in vivo and nucleosomics of cell-free DNA
References