Introduction
Cancer represents one of the most life-threatening diseases posing a
major health challenge all over the world(Li, Xu, Ding, & Tang, 2019).
Urothelial cell carcinoma (UCC) also known as bladder cancer is among
the principal causes of cancer-related deaths globally(Garg, 2016;
Kobayashi, 2016). The incidence of bladder cancer is ranked
9th with a total number of 549,393 new cases and
199,922 deaths globally(Bray et al., 2018; Saginala et al., 2020). These
numbers are forecasted to double in 2040, particularly in the developed
countries, signifying a severe health crisis in the future which can
lead to financial burden on countries due to the exorbitant treatments,
high recurrence rates and subsequent need for long-term follow-up(Leal,
Luengo-Fernandez, Sullivan, & Witjes, 2016; Soria et al., 2018).
Urothelial cell carcinoma is reported to be the second most frequent
malignant tumour of the genitourinary tract with men at risk four times
higher than women. The most common bladder cancer is transitional cell
carcinoma (TCC) or urothelial cell carcinoma (UCC), classified into;
non-muscle-invasive bladder cancers (NMIBCs) and muscle-invasive bladder
cancers (MIBCs). The NMIBCs accounts for about 70-80 percent of all
diagnosed patients, with the tendency of future recurrences and may
advance into muscle-invasive bladder cancers(Gao et al., 2020). Whereas
MIBCs accounts for about 20-25 percent of patients, signifying an
active, locally invasive carcinoma with a metastatic
potential.10
Despite diagnostic and therapeutic advances for UCC, if it is not
detected early, will remain a big challenge. Although there have been
great achievements in its management and treatments that include
surgical procedures, radiotherapy, pre- and post-operative treatments
and chemotherapy have been made, there has been no significant progress
in survival rates for bladder cancer patients.11Moreover, these treatments are presented with various side effects that
lead to other health problems.4 As a result,
healthcare providers receive substantial number of cases with relapse
and progression, leading to long-term follow-up. All these challenges
made bladder cancer an expensive disease to manage.7The need to identify novel molecular markers in bladder cancer in order
to predict medical outcomes, especially in patients with relapse has
made researchers in recent years to focus more on the molecular aspects
of the disease with the aim of boosting its biological understanding in
order to unravel the molecular factors that can be utilized as targets
for therapies and guiding assessment of risk and help in informed
decision making in clinical practice.12
Transcriptomic technologies employ methods that study and quantify
organism’s transcriptome,13 a complete set of RNA
transcripts in a cell for a specific developmental stage or
physiological state. Understanding transcriptome is essential for
interpreting the functional elements of the genome and revealing the
molecular constituents of the cells and tissues to better understand the
development of diseases.14 Identifying transcripts and
quantifying the level of gene expression have been the major focus in
molecular biology since the discovery of the RNA as an essential
intermediate between the genome and the proteome.15The last decades have witnessed the use of microarray technology and
bioinformatic analysis in screening genetic changes at the genome level
which has greatly assisted in the identification of differentially
expressed genes (DEGs) and functional pathways implicated in
cancer.16 However, with technological advancement and
elucidation of noncoding RNAs, transcriptomic approaches have given room
for deeper understanding of the intricacies of the regulation of gene
expression, alternate splicing events, functions of noncoding RNAs and
ascertaining the importance of such approaches in the correct
construction and annotation of complex genomes.1
Furthermore, high-throughput RNA sequencing (RNA-Seq) has opened
opportunities for transcriptomic studies and has advanced into a
standard technique used in biomedical studies. This technique is
currently utilized in the estimation of gene expression, identification
of noncoding genes, discovery of new genomic characteristics and drug
discoveries. It is well established that RNA-Seq has strong advantages
over the previously developed sequencing
techniques.17 This makes RNA-Seq a vital tool in
cancer biology that can be exploited for tumour classification, patient
stratification and monitoring of patients’ response to
therapy.18 However, despite the high level of
correlation that exists between RNA-Seq and other techniques such as
microarray, studies have strongly emphasised the merits of RNA-Seq over
the other techniques.19 The discovery of gene fusion
and differential expression of RNA transcripts that are known for
causing diseases are some of the prospects of the
RNA-Seq.20 In this review, we summarized the current
literature status of transcriptomic studies carried out on urothelial
cell carcinoma and identified the possible areas for future research.