Liquid Biopsy Biomarkers in Bladder Cancer: A Current Need for Patient Diagnosis and Monitoring

Abstract

Bladder Cancer (BC) represents a clinical and social challenge due to its high incidence and recurrence rates, as well as the limited advances in effective disease management. Currently, a combination of cytology and cystoscopy is the routinely used methodology for diagnosis, prognosis and disease surveillance. However, both the poor sensitivity of cytology tests as well as the high invasiveness and big variation in tumour stage and grade interpretation using cystoscopy, emphasizes the urgent need for improvements in BC clinical guidance. Liquid biopsy represents a new non-invasive approach that has been extensively studied over the last decade and holds great promise. Even though its clinical use is still compromised, multiple studies have recently focused on the potential application of biomarkers in liquid biopsies for BC, including circulating tumour cells and DNA, RNAs, proteins and peptides, metabolites and extracellular vesicles. In this review, we summarize the present knowledge on the different types of biomarkers, their potential use in liquid biopsy and clinical applications in BC.

Keywords: biomarkers; bladder cancer; liquid biopsy.

Figure 1

Liquid biopsy samples and biomarkers. Liquid biopsy samples include urine, serum, plasma, saliva, cerebrospinal and pleural fluid, among others. In BC, the liquid biopsies more widely used as detection and surveillance systems are urine (by its intimate contact with the tumour), as well as serum and plasma, which allow the follow-up of advanced disease. These liquid biopsies present several biomarkers, such as circulating tumour cells (CTCs), circulating cell-free tumour DNA (ctDNA), RNAs, proteins, metabolites and extracellular vesicles (EVs). Additionally, exfoliated cells derived from a tumour can be found in urine.

Figure 2

CTC and ctDNA processing methods. Scheme showing some enrichment techniques to isolate CTCs from peripheral blood cells (erythrocytes and leukocytes) and different detection systems based on immunomagnetic assays, using specific antibodies to recognize antigens present in tumour cells (like EpCAM or cytokeratins) as well as to exclude leukocytes (using antibodies against CD45) (left panel). Right panel displays the different DNA alterations (including mutations, copy number variations (CNVs), gene rearrangements or methylation variations) which can be analysed from ctDNA, as well as different detection methods and their correspondent limit of detection.

Figure 3

Hypothetical flowchart of liquid biopsies management in BC. In NMIBC patients, urine could be the best type of biofluid for diagnosis, prognosis, surveillance and therapy response due to its intimate contact with the tumour, whilst in MIBC patients, though urine could also be used, plasma and serum acquire more importance to monitor patients.