Liquid biopsy definition, research and when to use
What is a cancer liquid biopsy?
Liquid biopsies are tests that use blood or other body fluids to find out if someone has cancer, to determine the best options for treatment, or to monitor how patients respond to treatment. The earliest liquid biopsies involved looking at chromosomes under a microscope to find abnormalities, specifically to find out if patients had certain types of leukemia. In the past 20 years, advances in technology have made liquid biopsies more useful. Now they can detect cancer early, classify diseases, check for small amounts of remaining disease, and even assess the risk of developing a disease by measuring different substances in the blood, like DNA and proteins.
What does the research on liquid biopsies show?
Recently, the company Grail conducted a study involving 15,000 patients at 142 different sites. They wanted to see how well different liquid biopsy tests could detect various types of cancer. The tests looked for 1) mutations in genes, 2) abnormalities in the number of copies of certain genes (CNA), and 3) specific patterns of chemical changes in DNA called methylation. The mutation tests had high specificity (a positive result is typically associated with the presence of cancer), but they often gave false negatives (low sensitivity). They also weren’t ideal for pinpointing where the cancer might be. The CNA tests had moderate accuracy, acceptable sensitivity, but not-so-great ability to locate the cancer. The methylation tests performed the best and were chosen for further development. They led to the creation of the Galleri test.
Ongoing studies are being conducted to see how useful the Galleri multi-cancer early detection test is in improving patient outcomes. The recently completed Pathfinder study tested over 10,000 patients between the ages of 40 and 77, from seven different health systems. The test found signs of cancer in 1.4% of the patients, with the highest percentage in high-risk populations. They confirmed 36 different types of cancer in 35 individuals. Initial analysis showed that the test was 97% accurate in identifying the most likely type of cancer based on the affected tissue. Further analysis revealed that 0.9% of the population had cancer, and the test had a 99.1% specificity (ruling out cancer when it wasn’t present), and a 43% rate of cancer when it was present.
What are some other examples of liquid biopsy tests?
CellSearch® assay (by Menarini Silicon Biosystems), detects circulating tumor cells in patients with metastatic breast cancer, prostate cancer, or colorectal cancer. CellSearch, originally developed by Janssen (a division of J&J), was approved by the FDA in 2004, and while the test has not been universally adopted, various studies suggest that it has value in the management of patients with these conditions.
Other liquid biopsy tests include EpiSwitch™ (Oxford BioDynamics), Guardant Reveal™ (Guardant Health) MRD (Minimal Residual Disease) test, Cologuard® (Exact Sciences), and others. These tests have major advantages, including being non-invasive and having relatively high specificity (positive result is typically associated with the presence of cancer). However, they all have the drawbacks of modest to low sensitivity (giving frequent false negatives) and unclear directions of action. In addition, because the markets are competitive, there is a lack of transparency about the methods and details of the tests. This leaves healthcare providers to make decisions without knowledge of what is being measured.
Are there liquid biopsy tests available for my pet?
Liquid biopsy testing is an emerging field in veterinary medicine, but the lack of regulation adds to the uncertainty of testing. PetDx (OncoK9®) and Volition (Nu.Q®) are among the companies offering versions of liquid biopsy testing for cancer. These tests have the same limitations as tests developed for human patients. However, they offer fewer benefits because there are fewer options for precision guided treatments in veterinary medicine, and because the testing (and subsequent tests recommended by the results) are not generally covered by insurance.