Cancer diagnoses usually require a surgical biopsy—removal and examination of the suspicious tissue for signs of cancer. Liquid biopsies offer a simpler and less painful alternative.
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Surgical biopsies are often highly invasive if they can be performed at all.
In contrast, liquid biopsies are tests that detect the presence of cancer using blood, urine, saliva, or other bodily fluids. This technique is possible because cancerous tissues shed cells, DNA, and tiny lipid-encased vesicles called exosomes that contain cancer-associated biomarkers.
A biomarker—short for “biological marker”—is a molecule objectively measured to indicate disease.
Why Liquid Biopsies Matter
Surgical biopsies are often expensive and difficult to procure. Liquid biopsies offer an alternative testing method using a blood draw or other fluid collection kit, which saves time, money, pain, and potential complications.
Three types of liquid biopsies are in various phases of development:
- Cell-free DNA (cfDNA) liquid biopsies identify the DNA released when cancer cells die. This diagnostic identifies cancer-specific mutations using tools such as PCR or next-generation sequencing analysis.
- Exosome liquid biopsies collect and identify exosomes as cancer-associated by examining the enclosed DNA or RNA.
- Circulating tumor cell (CTC) liquid biopsies identify cells splintered from a tumor and circulating in the bloodstream through tumor-specific proteins on their surfaces.
Bench to Bedside
Four liquid biopsy tests are currently FDA-approved:
- Cell Search® CTC Test: detects circulating tumor cells
- cobas® EGFR Mutation Test v2: detects a common lung cancer mutation in the EGFR gene in circulating tumor DNA
- Guardant360® CDx: detects circulating tumor DNA
- FoundationOne® Liquid CDx: detects circulating tumor DNA
- cfDNA: cell-free DNA
- CTC: circulating tumor cells
- ctDNA: circulating tumor DNA
- CDx: companion diagnostics
Today, liquid biopsies primarily monitor the progress of or response to cancer treatment rather than initial diagnostic tests. A major goal in the liquid biopsy field is to develop tests that routinely detect cancer in seemingly healthy people; generally, early detection translates to better treatment outcomes.
A study assessing the efficacy of a cfDNA blood biopsy test detected no tumor DNA in the blood of roughly 15 percent of cancer patients. This poor result highlights the need to combine different diagnostic approaches to detect cancer in body fluids.
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