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. Later this year, the Cancer Screening Research Network, a clinical trials network coordinated by the Fred Hutchinson Cancer Center, will launch a liquid biopsy pilot study. Known as the Vanguard study, 24,000 participants will determine the feasibility of using liquid biopsy tests in future randomized controlled trials.

10,000 ft View

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.

Tricky Terms

A biomarker—short for “biological marker”—is a molecule objectively measured to indicate disease. For example, prostate-specific antigen (PSA) is a protein used as a biomarker for prostate cancer. Human epidermal growth factor receptor 2 (HER2) is a protein that, when overexpressed, is a biomarker for some breast and gastric cancers.

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.  

Applied Science

Three types of liquid biopsies are in various phases of development:

1. 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.
2. Exosome liquid biopsies collect and identify exosomes as cancer-associated by examining the enclosed DNA or RNA. 
3. 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:

1. Cell Search® CTC Test: detects circulating tumor cells 
2. cobas® EGFR Mutation Test v2: detects a common lung cancer mutation in the EGFR gene in circulating tumor DNA
3. Guardant360® CDx: detects circulating tumor DNA
4. FoundationOne® Liquid CDx: detects circulating tumor DNA

Alphabet Soup

• cfDNA: cell-free DNA
• CTC: circulating tumor cells
• ctDNA: circulating tumor DNA
• CDx: companion diagnostics

Future Perfect

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.

Cocktail Fodder

Currently, ~20 cancer liquid biopsy tests are in development, each with its unique approach. They offer screening for a wide range of tumor types, from two to fifty, in a single test. Some tests, like Delfi’s FirstLook lung cancer test, focus on one cancer. Others, like Grail’s Galleri and Exact Sciences’ Cancerguard, screen for multiple cancers.

Bio Baffled?

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