It now seems likely that liquid biopsies will have a well-defined and important role in the diagnosis of cancer and the screening of treated cancer patients for recurrences. The value of the procedure continues to improve due to new scientific discoveries (see: Scientific Breakthrough on the Correlation of Liquid Biopsies with Cancer Type) and a recent article was the most positive of any that I have read about the value of liquid biopsies (see: Liquid Biopsy Is Effective at Guiding Treatment of Lung Cancer, Study Finds). Below is an excerpt from it:
...[T]wo years ago, Dr. Li and his colleagues [at Memorial Sloan Kettering] began a prospective clinical study to evaluate whether a liquid biopsy test could help guide treatment decisions for people with lung cancer....The authors conclude that liquid biopsy–guided treatment is “feasible, rapid, and useful.”....[Patients in the study] all had advanced-stage non-small cell lung cancer that either had no known mutation that could be targeted with a drug or had stopped responding to a targeted therapy. Their cancers had spread beyond the primary location. Each patient had the liquid biopsy test performed on a blood sample. About half of the patients (106) also had their tumor tissue genetically sequenced by MSK’s DNA-sequencing platform, called MSK-IMPACT, [a targeted test for mutations]. Among the most important benefits of the liquid biopsy was the quick turnaround time..... In the study, just over 45% of the patients were found by liquid biopsy to have a mutation that could be targeted by an approved or investigational drug. About 22% of the patients (46 people) received one such drug, and nearly all of them experienced a benefit — namely, a decrease in the size of their tumors.
The particular liquid biopsy test used in this study is made by Resolution Bioscience, a biotech company.... It looks for mutations in 21 genes that are known to be involved in non-small cell lung cancer. By comparing the results of the liquid biopsy to those of tumor tissue, the team determined that the overall concordance rate between the two approaches was 56.6%. This means that for a little more than half of the people, both tests identified at least one mutation in common. What cheered the team more was that when they looked just at people who tested positive for a cancer mutation on the liquid biopsy, 89.6% had that same mutation also identified by the test of tumor tissue. Finally, when the investigators looked at only patients with driver mutations found on the liquid biopsy — those that matter most in terms of treatment — the rate of agreement between the two tests was 96.1%.
As I reflect on the advances that have been made made with regard to liquid biopsies, I recall that there has been speculation for decades that surgical pathology could be replaced some day by some sort of "biochemical analysis" of malignant tissue. My personal understanding of how this would work was very vague but involved the idea that the malignant tumors were biochemically different in some ways from normal tissue. It now turns out that the "biochemical process" underlying liquid biopsies is the genomic analysis of cell-free circulating tumor DNA which has known differences from normal DNA.
The major advantage that a liquid biopsy holds over normal histopathological examination of paraffin-embedded tissue by a pathologist is the possible avoidance, one day, of the need for a biopsy. Tumors will often be located in inaccessible places which makes the liquid biopsy, if reliable, very attractive. The question then arises as to what extent liquid biopsies will replace physical biopsies in the future. It's premature to speculate about such a question. We don't have answers yet as to whether a cancer in its early stages releases cells into the circulation and whether cell-free DNA from such early lesions can be detected.
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