When a patient is having chest pain and trouble breathing, there are many potential lung problems that can cause these symptoms, one of them being lung cancer. If the doctor suspects that there could be a tumor in the lungs, she runs some tests. The best way to determine if there is a cancerous tumor is to do a biopsy, in which the doctor performs surgery to remove a tissue sample.
But a new technique known as a liquid biopsy can be used by doctors to screen for non-small cell lung cancer, the most common type of lung cancer. Liquid biopsies will not completely eliminate biopsies for a variety of reasons, but the benefits of liquid biopsies make the technique a great development in cancer research—one that is surely here to stay.
Difference Between a Biopsy and a Liquid Biopsy
While a typical biopsy requires an invasive surgery, lung cancer detection with a liquid biopsy only requires a blood sample. This immediately has two great advantages: a lower cost and a simple, non-invasive procedure. Another advantage is speed. A liquid biopsy returns results in 9 days, while a typical biopsy requires 20.
Basics of Liquid Biopsies
When I first learned about liquid biopsies, I had to wonder how blood, that circulates throughout the body, can tell us if a patient has a cancerous tumor in the lungs. The key, it turns out, is biomarkers.
A biomarker is like a footprint you might find in the woods. You don’t see the bear itself, but you can figure out quickly that the footprint means a bear must be close by.
In tumors, the cancerous cells emit a certain biomarker that doctors call ctDNA—or circulating tumor DNA—little pieces of DNA that exist in the blood and signal that a tumor is present in the body.
Because liquid biopsies detect even small amounts of miniscule molecules, ctDNA produce results 6-12 months earlier than a cancer diagnosis based on imaging, such as a CT Scan, as one study found in 2017. Beyond this, cancer testing via liquid biopsies also reduces patient exposure to radiation, reducing the chance of other diseases when radiation exposure is high.
Monitoring Cancer with Liquid Biopsies
Because liquid biopsies are non-invasive and have quicker turnaround times, they make for great tests not just to detect cancer, but also to monitor its progression overtime. There is a correlation between the amount of ctDNA—the footprints that doctors use to detect cancer—and the severity of the cancer in the lungs. In other words, a decrease in the amount of ctDNA detected by the liquid biopsy suggests that the size of the tumor is decreasing.
Current liquid biopsy techniques are not perfect because of the test’s specificity. A test is very specific if it rarely shows false negatives. A false negative result, in this case, means that the test concluded that there is no cancer when, in fact, there really is a tumor in the lungs. Because liquid biopsies yield false negative results at too high of a rate, doctors often need to perform other tests to confirm a liquid biopsy test that returns a negative. With our bear in the woods analogy, it would be like we concluded that there was no bear in the woods because we did not find any tracks.
Liquid biopsies clearly have their advantages and disadvantages. While the test is great at detecting the presence of cancerous tumors, the high rate of false negative results does not allow doctors to stop performing invasive biopsies, which still remain the pinnacle of cancer detection. It is clear, however, that the cost and speed advantages make liquid biopsies a great tool in the doctor’s toolkit for detecting and monitoring the growth of cancerous tumors in the lungs.
Liquid biopsies are not only done for lung cancers, there is also research that shows a similar method can be used for breast cancer. The liquid biopsy test is just another piece of the growing move to individualized care for cancer. It won’t replace all other cancer testing, but it is sure to be a mainstay in cancer treatment.
Tontonoz, Matthew (2018). Liquid Biopsy Is Effective at Guiding Treatment of Lung Cancer, Study Finds. Memorial Sloan Kettering Cancer Center, https://www.mskcc.org/news/liquid-biopsy-effective-guiding-treatment-lung-cancer-study-finds.
U.S National Library of Medicine (2020). What is circulating tumor DNA and how is it used to diagnose and manage cancer? Medline Plus, https://medlineplus.gov/genetics/understanding/testing/circulatingtumordna/
Tucker, Nichole (2020). What’s Driving, and Blocking the Liquid Biopsy Evolution in Non–Small Cell Lung Cancer? Targeted Oncology, https://www.targetedonc.com/view/what-s-driving-and-blocking-the-liquid-biopsy-evolution-in-non-small-cell-lung-cancer
Revelo, A. E., Martin, A., Velasquez, R., Kulandaisamy, P. C., Bustamante, J., Keshishyan, S., & Otterson, G. (2019). Liquid biopsy for lung cancers: an update on recent developments. Annals of translational medicine, 7(15), 349. https://doi.org/10.21037/atm.2019.03.28. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6712255/
Jamal-Hanjani, M., Wilson, G. A., McGranahan, N., Birkbak, N. J., Watkins, T. B., Veeriah, S., & Salm, M. (2017). Tracking the evolution of non–small-cell lung cancer. New England Journal of Medicine, 376(22), 2109-2121. https://www.nejm.org/doi/full/10.1056/NEJMoa1616288.
Rolfo, C., Russo, A (2020). Liquid biopsy for early stage lung cancer moves ever closer. Nat Rev Clin Oncol 17, 523–524. https://doi.org/10.1038/s41571-020-0393-z.