What is a Liquid Biopsy?

Introduction

A liquid biopsy, fluid phase biopsy, or fluid biopsy is a procedure where biological tissue is obtained for sampling and analysis. It is a revolutionary technique that allows new perspectives. It involves the isolation and detection of circulating tumor DNA, circulating tumor cells. And as a source of proteomic and genomic information for individuals with cancer. For many years, healthcare professionals and researchers have tried to find a fast and easy way to diagnose and monitor cancer. This is a technique that can be used to diagnose and monitor diseases such as cancer as it has a benefit of not being too invasive. It can, therefore, be used more frequently for the tracking of tumors, mutations, and validation of cancer treatment efficacy. It can also be used to monitor relapse among patients after their treatment. The liquid refers to samples such as blood or other bodily fluid. 

Types

Depending on the condition of the liquid biopsy, there are several types of liquid biopsy such as:

  • Circulating endothelial cells (CECs) – This can be used in the diagnosis of a heart attack.

  • Cell-free fetal DNA (cffDNA) – This is used for prenatal diagnosis where samples can be obtained from amniotic fluid or maternal blood.

  • Circulating tumor DNA (ctDNA) – This is used for cancer studies. ctDNA are tiny DNA fragments present in the blood as they break away from the tumors. ctDNA can be used to monitor the treatment progress as ctDNA levels are expected to decrease once the tumor has been removed or shrinks. When ctDNA levels in the blood increase, it could signify a recurrence of cancer. Since ctDNA levels increase several months before the cancer recurs, it allows for faster treatment response. 

Various biomarkers can be studied for the detection of other diseases. A good example would be the isolation of protoporphyrin IX for the diagnosis of atherosclerosis. In the study of the central nervous system, both blood and cerebrospinal fluid can be sampled. 

Current Issues in Liquid Biopsy Research

Some ongoing issues related to liquid biopsy research include:

  1. Cancer location identification

This can be done by using the cell free DNA present in the blood to detect the presence of cancer in the body before it becomes visible through other techniques such as mammography, x-rays, colonoscopy, or CT scans. Since the cancer is yet to be visible, physicians need a screening tool that offers guidance on where they can look for cancer. One recent study showed the combination of technologies where protein markers and cell free DNA are observed for different cancer types. With that combination, researchers were able to sort for ctDNA and link the available information to a protein marker which offers clues on where cancer may be located. 

  1. Tiny amounts of ctDNA

Even with significant sized tumors, there is only a very small amount of ctDNA. There are various types of DNA circulating in the blood as seen in pregnant women or those who have suffered a stroke or heart attack. All these DNA fragments are known as cell free DNA. Due to the various DNA fragments that are present in the blood, the researchers should be able to accurately identify ctDNA from other DNA to avoid false positives 

Liquid Biopsy Future

The future of liquid biopsy largely depends on several factors such as:

  1. Catching up to technology

Since technology is advancing rapidly, the ability to analyze the impact of the technology and the best way to use it is left behind. It can be difficult as it takes time, effort, and practice to understand how to use the data that has been collected through translational science. In some centers, artificial intelligence is being used to obtain answer or recognition from data. 

  1. Translation for undiagnosed individuals

This is required to obtain more data regarding the efficacy of liquid biopsy as a screening procedure such as for individuals who have no evidence of cancer.

  1. Safety

The liquid biopsy test is a safe procedure that provides accurate results. Ideally, a liquid biopsy should be able to be used in the detection of cancer in the body, to tell if the individual should be treated, location of cancer, and best treatment options for the most favorable prognosis.

  1. Funding

Research regarding liquid biopsy is important as it helps advance this field of science. While a lot has been achieved, there is still a long way to go. 

Conclusion

Liquid biopsy is a technique that can address various issues. It involves the identification and isolation of circulating tumor cells, ctDNA, exosomes, and various information in patients with cancer. With new techniques, liquid biopsy now has a wide application such as in prognosis, diagnosis, screenings, prediction, and monitoring or treatment efficacy. Further research is necessary to help advance this field. 

References:

  1. Palmirotta R, Lovero D, Cafforio P, et al. Liquid biopsy of cancer: a multimodal diagnostic tool in clinical oncology. Ther Adv Med Oncol. 2018;10:1758835918794630. Published 2018 Aug 29. doi:10.1177/1758835918794630

  2. Liquid biopsy. Wikipedia. Accessed 5/9/2019. https://en.wikipedia.org/wiki/Liquid_biopsy

  3. McDowell S. Liquid biopsies: past, present, future. American Cancer Society. Accessed 5/9/2019. https://www.cancer.org/latest-news/liquid-biopsies-past-present-future.html