Liquid Biopsy

What is a liquid biopsy?

A liquid biopsy is a blood test sometimes used to detect cancer. It can detect tumor cells, which have broken off from a tumor and entered the bloodstream. These are called circulating tumor cells. It can also detect fragments of DNA from the tumor in the blood, called circulating tumor DNA (or ctDNA). These fragments of ctDNA contain genetic information about the cancer cell’s behavior.

What is the difference between a liquid biopsy and a biopsy?

A biopsy takes a sample of tissue directly from the tumor to test for cancer. A liquid biopsy is blood sample taken to test for evidence or signs of cancer, such as tumor cells and tumor DNA.

A biopsy is the gold standard procedure when diagnosing cancer. If a tumor is present, it isn’t guaranteed to show signs that are detectable in a blood sample.

However, when a liquid biopsy does detect cancer, it can offer valuable information about the cancer which can help in treatment planning.

When is a liquid biopsy performed?

A liquid biopsy may be recommended for screening (for certain cancers in certain patients), if you have advanced cancer (cancer which has spread or metastasized) or if your current treatment isn’t working.

Metastatic cancer has spread from the site of the original tumor. As it spreads to other parts of the body, pieces of the tumor break off and travel through the blood.

A liquid biopsy may be recommended to:

• Screen for cancer: To improve adherence of colorectal cancer screening, a liquid biopsy test may be offered to patients who are not up to date with their colorectal cancer screening and who are not willing/able to have a colonoscopy or FIT (fecal immunochemical test).
• Determine a prognosis: The number of CTCs identified can give an indication of outcome. Doctors may perform ongoing tests to monitor your condition and adjust your treatment if needed.
• Inform treatment decisions: A liquid biopsy can indicate which types of targeted treatment you may be a good candidate for. As liquid biopsies give information about the cancer cells DNA, and targeted therapy works by destroying certain types of cancer cells, the test can therefore detect certain characteristics of the tumor and the most appropriate treatment be given.
• When a biopsy isn’t possible: Biopsies are more invasive that a liquid biopsy. If a tumor is hard to access, a liquid biopsy may be recommended.

Liquid biopsy and colorectal cancer

There are different types of liquid biopsy test available and many more are at different stages of research and development.

One type of liquid biopsy test that is approved for use to screen for colorectal cancer, is designed to provide an option for patients who may refuse standard tests like colonoscopy or FIT.

Another type of liquid biopsy test is sometimes used in patients with metastatic colorectal cancer. It is a test that can detect circulating tumor cells and is useful in monitoring cancer and providing prognosis.

Does a liquid biopsy replace a colonoscopy?

It is important to note that a liquid biopsy does not replace a colonoscopy. Colonoscopy is the gold standard for colorectal cancer screening, due to its proven track record in reducing the incidence of and number of deaths from colorectal cancer.

A colonoscopy has several advantages over a liquid biopsy:

• Direct visualization and intervention: Colonoscopy allows doctors to directly visualize the entire colon and rectum, identifying abnormalities such as polyps or tumors. It also enables immediate removal of polyps or biopsy of suspicious lesions during the procedure.
• Diagnostic accuracy: Colonoscopy is more accurate in detecting early-stage colorectal cancer and pre-cancerous changes compared to liquid biopsy. This makes it more reliable for comprehensive screening and prevention.
• Limited information: While a liquid biopsy can detect circulating tumor DNA or specific biomarkers in the blood, it doesn’t give detailed information about the location, size, or stage of the tumor.
• Screening limitations: Although liquid biopsy may be considered as a screening tool for colorectal cancer, it is not approved for screening colorectal cancer precursors (like advanced precancerous polyps). A liquid biopsy may be recommended for certain patient populations under certain circumstances, rather than as a replacement for colonoscopy. Patients who meet any of the following criteria might be candidates for liquid biopsy:
• Patients who can’t have a colonoscopy: This may be due to medical conditions that make colonoscopy unsafe, such as severe heart or lung diseases, or those who cannot tolerate sedation.
• High-risk or reluctant patients: Patients who are at high risk of complications from invasive procedures or those who refuse to undergo colonoscopy despite its recommendation.
• High-risk patients: Those with a family history of colorectal cancer or known genetic predispositions, where regular monitoring is necessary, and colonoscopy frequency may need to be supplemented with non-invasive tests.
• Post-treatment surveillance: For patients with a history of colorectal cancer, a liquid biopsy can be used to monitor for recurrence or progression alongside standard follow-up protocols.
• When traditional methods are inconclusive: If stool-based tests, imaging, or other non-invasive methods are inconclusive then liquid biopsy may be recommended before more invasive diagnostics are performed.

Liquid biopsy tests have the potential to aid in the diagnosis and monitoring of certain cancers, like colorectal cancer, in certain patients. It is important to remember that a liquid biopsy is not a replacement for routine colorectal cancer screening.

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