Liquid biopsy tests hold much promise. But inconsistencies in their findings provoke scrutiny and calls from researchers for further development before they can be considered reliable enough for diagnostic use
Many commercial developers of liquid biopsy tests tout the accuracy and benefits of their diagnostic technology. However, there are an equal number of medical laboratory experts who believe that this technology is not yet reliable enough for clinical use. Critics also point out that these tests are being offered as Laboratory Developed Tests (LDTs), which are internally developed and validated and have not undergone regulatory review.
Dark Daily has published several e-briefings on researchers who have sent the same patient samples to different genetic testing labs and received back materially different test results. Now, a new study by Johns Hopkins University concludes that liquid biopsy technology “must improve” before it should be relied upon for diagnostic and treatment decision making.
‘Certification for Medical Laboratories Must Improve’
Liquid Biopsy is the term for drawing whole blood and looking for cancer/tumor cells circulating in the blood stream. This is one factor in the imprecision of a liquid biopsy. Did the blood sample drawn actually have tumor cells? After all, only a limited number of tumor cells, if present, are in circulation.
Researchers at The James Buchanan Brady Urological Institute at Johns Hopkins School of Medicine know this and recently compared results of two liquid biopsy tests to determine which one would be more beneficial for patients. They published their findings in the December issue of JAMA Oncology.
To perform the study, researchers collected blood samples from 40 patients with metastatic prostate cancer and sent the same patient samples to two different Clinical Laboratory Improvement Amendments (CLIA) licensed College of American Pathologists (CAP) accredited laboratories. The labs then performed DNA next-generation sequencing on the samples following the directions of the two liquid biopsy manufacturers.
In reporting the DNA findings and results from the two medical laboratory companies, researchers discovered that the results completely matched in only three of the 40 patients! The Johns Hopkins researchers are concerned that patients could be prescribed certain cancer treatments based on which lab company’s liquid biopsy test their physician orders, instead of an accurate identification of the unique mutations in their tumors.
“Liquid biopsy is a promising technology, with an exceptional potential to impact our ability to treat patients, but it is a new technology that may need more time and experience to improve,” Gonzalo Torga, MD, Postdoctoral Fellow and Instructor at Johns Hopkins, and the lead author of the study, told Forbes. “We can’t tell from these studies which laboratory’s panel is better, but we can say that certification for these laboratories must improve.”
Unlocking New View of Tumors
Two commercial tests were used for the study:
Guardant360 from Guardant Health, Inc., uses digital sequencing to analyze genomic data points at the single molecular level. It examines 73 genes, including all National Comprehensive Cancer Network (NCCN) listed genes. The test searches for DNA fragments among billions of cells and digitally tags each fragment. This process unlocks a view of tumors that is not seen with tissue biopsies, which helps doctors prescribe the best treatment options for a particular patient.
“As a simple blood test, it provides physicians with a streamlined, cost-effective method to identify genomic alterations that can comprehensively influence a patient’s therapy response,” Helmy Eltoukhy, PhD, co-founder and Chief Executive Officer at Guardant Health, told MDBR.
“The only way of keeping ahead of those diseases and tracking those mutations has been through surgery, through doing a tissue biopsy and physically cutting a piece of the tumor out and sequencing it,” Eltoukhy noted in an interview with Xconomy. “What we’re able to do is essentially get the same, or sometimes better performance to tissue biopsy, but through two teaspoons of blood.”
According to the Guardant Health website, it takes just 14 days for a full report from Guardant360 to reach the ordering physician. In addition, the blood test provides samples with an adequate level of cell-free DNA to test 99.8% of the time and reduces errors and false positives found in standard sequencing methods by 1,000 times. It is common for samples used for tissue sequencing to have insufficient DNA for testing 20% to 40% of the time.
“We believe that conquering cancer is at its core a big data problem, and researchers have been data-starved,” explained Eltoukhy in VentureBeat. “Our launch of the world’s first commercial comprehensive liquid biopsy sparked a boom in cancer data acquisition. Every physician who orders one of our tests, and every patient whose tumor DNA we sequence, adds to this larger mission by improving our understanding of this complex disease.”
PlasmaSELECT-R64, manufactured by Personal Genome Diagnostics (PGDx), evaluates a targeted panel of 64 genes that have biological and functional relevance in making treatment decisions. PGDx announced the expanded version of its PlasmaSELECT assay in March of 2017.
“We are proud to launch the revolutionary PlasmaSELECT 64 expanded assay just six months after we introduced the most accurate, clinically actionable liquid biopsy tumor profiling assay to the market,” said Doug Ward, Chief Executive Officer at PGDx, in a press release. “This update is the first liquid biopsy assay that includes MSI (microsatellite instability) testing as a biomarker for high tumor mutational load, thereby providing cancer patients and their oncologists with information on whether they might be candidates for immuno-oncology therapies. The ability to generate DNA tumor profiling non-invasively using blood or plasma offers many advantages and makes genomic testing more accessible and usable.”
Regulations of LDTs Could be Needed to Improve Liquid Biopsy Tests
There are pathologists and clinical laboratory professionals who believe the technology behind liquid biopsies is not yet reliable enough for clinical use. The tests are being offered as LDTs, which are internally developed and validated, and the Food and Drug Administration (FDA) allows LDTs to be sold without regulatory reviews at this time. However, there are discussions regarding if and how to regulate LDTs, the outcome of which could impact how clinical laboratories are allowed to market the LDTs they develop.
Clearly, liquid biopsies are still in their relatively early stages of development. More testing and evaluation is needed to determine their efficacy. However, their potential to revolutionize cancer detection and care is obvious and a strong motivator for LTD developers, which means there will be future developments worth noting.