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.