Liquid Biopsy

The next frontier?

The term "liquid biopsy" refers to the non-invasive examination of biomarkers in biological fluids (such as blood, plasma, urine, liquor, and saliva) in order to detect and track the progression of cancer over time. This method circumvents the drawbacks of invasive procedures and provides sufficient molecular information similar to tissue biopsies. By tracking circulating proteins, cell free RNA, peripheral free circulating DNA (cfDNA), and other components, liquid biopsy enables early screening. Markers of cancer such circulating tumour cells (CTCs), circulating tumour DNA (ctDNA), and extracellular vesicles (Evs) can be found in peripheral blood and other bodily fluids and detected as a part of liquid biopsy.

Circulating tumor cells : Cancer cells known as CTCs separate from the main tumour and enter the bloodstream. Their resistance to anoikis allows them to survive in the bloodstream and avoid binding to the extracellular matrix (ECM). This resilience makes it possible to obtain CTCs by non-invasive methods, which makes it an effective tool for tracking and identifying cancer and its metastases. Currently a number of techniques for CTC analysis & detection. The CellSearch system, immunochemistry, flow cytometry, and reverse-transcriptase polymerase chain reaction are the most often employed techniques. The only platform authorised by the FDA is CellSearch.

Circulating Tumor DNA (ctDNA) : CfDNA makes up a sizable amount of the DNA released by tumours into the urine and peripheral circulation. As a result, whereas the majority of the DNA in plasma comes from healthy cells, a tiny amount of it comes from circulating tumour DNA (ctDNA) in cancer patients. In particular, ctDNA fragments released into the blood or urine can be used to identify epigenetic alterations linked to the onset and spread of cancers. One of the most important epigenetic mechanisms in bladder cancer is DNA methylation. DNA methyltransferases (DNMTs) often methylate CpG dinucleotides in human DNA, which results in transcriptional silence that prevents tumour growth and cancer cell invasion. The notion that DNA methylation contributes to the carcinogenesis and aggressiveness of cancer is supported by the fact that hypomethylation can happen in cancer patients. One study found that NMIBC had significant hypomethylation in comparison to other malignancies.

Extracellular Vesicle’s (EV’s) : All particle types that are spontaneously released by cells, have a lipid bilayer around them, and are incapable of replicating are referred to as “EVs.” After being discharged into bodily fluids, these vesicles release information that affects target cells.

For bladder cancer, the FDA has now authorised six urinary diagnostic assays for clinical use. Two of these measure proteins produced in the urine (NMP22 and BTA tests), while three of them (UroVysion, BladderCheck, and ImmunoCyt) identify changes in DNA, RNA, or proteins in urinary cells. These are currently being used as an adjunct to other tests in the clinical practice. 

For prostate cancer, due to the incredibly low sensitivity of commonly used analysis, liquid biopsy is not useful in the early stages of prostate cancer. For instance, ctDNA in patients with localised prostate cancer could not be detected by an ultra-lowpass whole-genome sequencing technique. However in studies, ctDNA tumour variants were found in two out of eight patients with localised disease prior to treatment, and they were linked to a very quick progression and recurrence of the disease. It is currently unclear how ctDNA detection can be used to forecast the course of early prostate tumours.

Thus, though various methods of liquid biopsy appear promising, further refinement and research is required before they can become a stand alone diagnostic tools and are currently used only as adjuncts. 

Dr Anuj Sharma

Max Super-speciality, Saket