Liquid biopsy: a step closer to transform diagnosis, prognosis and future of cancer treatments

Abstract

Over the past decade, invasive techniques for diagnosing and monitoring cancers are slowly being replaced by non-invasive methods such as liquid biopsy. Liquid biopsies have drastically revolutionized the field of clinical oncology, offering ease in tumor sampling, continuous monitoring by repeated sampling, devising personalized therapeutic regimens, and screening for therapeutic resistance. Liquid biopsies consist of isolating tumor-derived entities like circulating tumor cells, circulating tumor DNA, tumor extracellular vesicles, etc., present in the body fluids of patients with cancer, followed by an analysis of genomic and proteomic data contained within them. Methods for isolation and analysis of liquid biopsies have rapidly evolved over the past few years as described in the review, thus providing greater details about tumor characteristics such as tumor progression, tumor staging, heterogeneity, gene mutations, and clonal evolution, etc. Liquid biopsies from cancer patients have opened up newer avenues in detection and continuous monitoring, treatment based on precision medicine, and screening of markers for therapeutic resistance. Though the technology of liquid biopsies is still evolving, its non-invasive nature promises to open new eras in clinical oncology. The purpose of this review is to provide an overview of the current methodologies involved in liquid biopsies and their application in isolating tumor markers for detection, prognosis, and monitoring cancer treatment outcomes.

Keywords: Cancer; Circulating tumor DNA; Circulating tumor cells; Liquid biopsy; Non-invasive tumor detection; Precision medicine Cancer diagnosis; Tumor extracellular vesicles.

Fig. 1

Comparison of traditional tissue biopsy and liquid biopsy. The schematic illustrates the advantages that liquid biopsies have gained over traditional invasive surgical methods over the past decade. Shown here are methods of extracting a test sample which usually includes a small tissue fragment in case of tissue biopsies and blood in LBs. Analytes that are isolated and monitored in LBs include ctDNA, CTCs, and tumor EVs

Fig. 2

Entities analyzed in liquid biopsies and their application. The various analytes isolated from blood in LBs provide a wide variety of information regarding tumors. Each analyte has a specific application in tumor diagnosis, monitoring, and treatment as described

Fig. 3

Overview of CTC isolation, detection, characterization and clinical utility. Schematic illustrating various methods of CTC isolation and detection. CTCs must be filtered out from the rest of the cells in the blood like WBCs, RBCs, etc. (a) Isolation and enrichment methods include assays based on physical properties (like size, density, etc.) of CTCs, their tendency to bind/not bind antibodies and microfluidic properties that assist in filtering out CTCs from rest of the cells in the sample like plasma or serum. (b) Detection and characterization of CTCs involve various techniques that employ primers requiring prior information of gene sequence (left) relative to those are exclusively deep sequencing-based (right). PARE: Personalized analysis of rearranged ends; TAm-Seq: tagged amplicon deep sequencing; CAPP-Seq: Cancer personalized profiling by deep sequencing; Safe-SeqS: safe sequencing system; BEAMing: beads, emulsion, amplification & magnetic and draw clinically relevant information regarding tumors. (c) The section summarizes the application of CTCs in clinical oncology

Fig. 4

Extracellular vesicle biogenesis and cargo. (a) The schematic illustrates the synthesis of EVs (via endosomal sorting complex required for transport (ESCRT) dependent or independent pathway), inside the cell that begins by inward budding of the plasma membrane. Early endosomes formed to take up cytoplasmic cargo that includes biomolecules like DNA, RNA, and proteins that play a role in cell-to-cell communication. Multivesicular bodies, thus, formed containing a wide variety of cellular cargo, soon merge with plasma membrane releasing EVs. Cell-specific surface antigens are known to be tagged along in certain cases while EVs emerge from a cell. (b) The figure depicts the wide array of biomolecular cargo (both internalized and surface bearing) that EVs carry and exploited as markers in the characterization of tumors. Tumor derived EVs bearing numerous markers (as depicted) provide efficient noninvasive ways of LBs that offer real-time monitoring of tumor progression and treatment