|Purpose||analysis of non-solid biological tissue|
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. Therefore, it can also be done more frequently which can better track tumors and mutations over a duration of time. It may also be used to validate the efficiency of a cancer treatment drug by taking multiple liquid biopsy samples in the span of a few weeks. The technology may also prove beneficial for patients after treatment to monitor relapse.
Although only 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, its clinical implementation is not yet widespread.
There are several types of liquid biopsy methods; method selection depends on the condition that is being studied.
- In cancer studies, circulating tumor cells (CTCs) and/or circulating tumor DNA (ctDNA) are collected.
- In heart attack diagnosis, circulating endothelial cells (CECs) are sampled.
- In prenatal diagnosis, cell-free fetal DNA (cffDNA) is extracted from maternal blood. Amniotic fluid can also be extracted and analysed.
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. When studying the central nervous system, cerebrospinal fluid may be sampled instead of blood.
How it works
When tumor cells die, they release ctDNA into the blood. Cancer mutations in ctDNA mirror those found in traditional tumor biopsies, which allows them to be used as molecular biomarkers to track the disease. Scientists can purify and then analyze ctDNA using next-generation sequencing (NGS) or PCR-based methods such as digital PCR. 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. 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.
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