The Current Role of Circulating Biomarkers in Non-Muscle Invasive Bladder Cancer

Michael Rink; Heidi Schwarzenbach; Malte W. Vetterlein; Sabine Riethdorf; Armin Soave; on behalf of the EAU Young Academic Urologists—Urothelial Cancer Working party

Disclosures

Transl Androl Urol. 2019;8(1):61-75. 

In This Article

Abstract and Introduction

Abstract

Non-muscle invasive bladder cancer (NMIBC) is characterized by its high rate of disease recurrence and relevant disease progression rates. Up to today clinical models are insufficiently predicting outcomes for reliable patient counseling and treatment decision-making. This particularly is a serious problem in patients with high-risk NMIBC who are at high risk for failure of local treatment and thus candidates for early radical cystectomy or even systemic (neoadjuvant) chemotherapy. Next to its clinical variability, bladder cancer is genetically a highly heterogeneous disease. There is an essential need of biomarkers for improving clinical staging, real-time monitoring of disease with or without active treatment, as well as improved outcome prognostication. Liquid biopsies of circulating biomarkers in the blood and urine are promising non-invasive diagnostics that hold the potential facilitating these needs. In this review we report the latest data and evidence on cell-free circulating tumor desoxyribonucleic acid (ctDNA) and circulating tumor cells (CTC) in NMIBC. We summarize their current status in clinical diagnostics, discuss limitations and address future needs.

Introduction

Urothelial carcinoma of the bladder (UCB) is one of the most common epithelial malignancies among men and women ranking top ten in the western world.[1] At initial presentation, the majority of patients have non-muscle invasive bladder cancer (NMIBC), a disease that is potentially curable with transurethral resection of the bladder tumor (TURBT) with or without adjuvant instillation therapy.[2] Both, the natural history of NMIBC and its treatment strategies, are highly variable. In general, up to 70% of NMIBC patients eventually present with disease recurrence and 10–20% experience disease progression to muscle invasive bladder cancer (MIBC),[3] while overall survival usually is only marginally affected, if appropriate treatment is timely applied.[4] Indeed, while some patients never experience disease recurrence, others experience disease progression and eventually die of their disease.[5] Many efforts have been put into identifying risk factors particularly in NMIBC patients with high risk of disease recurrence and progression to optimize treatment recommendations with regard to adjuvant therapies.[6] In addition, identification of NMIBC patients at highest risk for disease progression that need more aggressive treatments including radical cystectomy and perioperative systemic chemotherapy is of crucial importance. Still, predicting the individual short- and long-term risk of disease recurrence and progression is mainly based on clinical and standard histopathological parameters. The two most common scoring systems and risk tables (i.e., the EORTC Genito-Urinary Cancer Group or the CUETO group) both only rely on clinic-pathologic parameter.[2,4] Meanwhile, several groups have analyzed the reliability of these scoring systems based on long-term outcome data and found that both previously mentioned models exhibit a poor discrimination for both disease recurrence and progression, respectively.[7] While clinical factors may indicate the risk for disease-specific endpoints in NMIBC, they do not account for the underlying genetics of each individual tumor.

Thus, it is important to consider that UCB is not only clinically, but also genetically a highly heterogeneous disease. The role of tissue biomarker has been extensively explored in NMIBC and subsets of biomarkers are routinely used in clinical practice for improved outcome prediction.[8] Biomolecular predictors hold the potential to unmask individual genomic, epigenetic, transcriptomic, and proteomic alterations.[4,9] Investigations on genomic variability may be performed on tissue, blood or urine samples in UCB. Of importance, several studies demonstrated relevant heterogeneity between the primary tumor and its metastasis in individual UCB patients that may explain the variable clinical course of disease.[10–12] Genetic variability and instability may be an indicator for aggressive cancer subclones and thus represent important targets even in early disease stages such as NMIBC.

Carcinogenesis is accompanied by deregulated tumor cell death and changes in proliferative processes, leading to increased levels of circulating cell-free desoxyribonucleic acid (cfDNA) in the surrounding body fluids of cancer patients. The physiological events leading to the release of cfDNA in human blood comprise processes such as apoptosis and necrosis along with active cell secretion.[13] While apoptotic cells produce DNA fragments of 180–200 bp or multiples of this unit and necrotic cells deliver higher molecular-weight DNA fragments in size of over 10,000 bp, both are cleared by macrophages for elimination.[14] Our experimental data have shown that cfDNA is highly fragmented[15] and exists predominantly as mono- and oligonucleosomes in the blood.[16,17] Its levels are generally higher than those of circulating tumor cells (CTC).[18] However, the majority of cfDNA in peripheral blood originates from leukocytes, and only a small fraction is circulating tumor desoxyribonucleic acid (ctDNA). Apart from the primary tumor, this ctDNA may derive from CTC and metastatic sites, and reflects their genetic and epigenetic alterations. Thus, in the blood, ctDNA forms a pool of diverse aberrations that may come from different sources, but may also remain unnoticed in biopsy specimens because of their heterogeneity. In NMIBC patients, the main sources of ctDNA are urine and blood, and most investigations were carried out using urine samples. Although urine, particularly from bladder cancer patients, is well eligible for cfDNA analyses, the fragmentation of cfDNA may be higher in urine than in plasma or serum, and therefore, could impair its analyses. However, in a seminal study from 1991, Sidransky et al. provided proof of the feasibility of urine-based ctDNA analyses in bladder cancer patients, and identified p53 gene mutations in cells from urine sediments.[19]

Tumor cell dissemination into the peripheral blood is an essential step during disease progression and prerequisite for development of distant metastasis. CTC are malignant epithelial cells captured in the circulation and potentially represent micrometastatic disease.[20] CTC are extremely rare (10−6) compared to other mono-nucleated blood cells.[21,22] Postulating CTC as surrogates for micrometastatic disease theoretically may change the treatment algorithm in NMIBC. While NMIBC usually is considered controllable with localized treatment without systemic chemotherapy, the presence of CTC in NMIBC may indicate the need of more aggressive treatment or even chemotherapy. In consequence, detection of CTC even in NMIBC has a significant potential in regards of more precise staging as well as outcome prediction.[23] Indeed, the impact of CTC in muscle-invasive and metastatic bladder cancer has been investigated in several studies,[24] but their advantage in early-stage bladder cancer remains unclear. The concept of liquid biopsy promotes the encouraging opportunity to detect and monitor disease together with therapy response without conventional biopsies or surgical excision of the primary tumor or its metastases.[24]

In this review, we summarize and discuss the current value of ctDNA and CTC in NMIBC. Circulating biomarkers, including ctDNA and CTC, are measured by non-invasive real-time techniques for dynamic disease surveillance and response monitoring.[20,25] We discuss the prognostic potential, clinical status as well as the limitation of these interesting biomarkers in the context of the most recent literature.

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