Current Cancer Biomarkers

Cancer is a major health problem and a leading cause of morbidity and mortality worldwide. The cancer burden can be reduced significantly using reliable, robust, sensitive, accurate, validated and specific biomarkers for early diagnosis, better prognosis and prediction. Traditionally, a number of biomolecules exhibit the potential to be used as diagnostic, prognostic and predictive biomarkers roles, however, they failed to be used in point-of-care settings for routine analysis. Recent advancements in sequencing techniques and analytical methods facilitate the development of novel and effective cancer biomarkers (liquid biopsies) with the fidelity of clinical application. These biomarkers provide personalized “omics” based information on the pathological state, molecular nature and biological aggressiveness of individual patients. Nevertheless, standardized platforms and/or methods for these biomarkers are yet to be established. Thus, adopting a combination of classical and new cancer biomarkers would offer a better understanding of the disease, resulting in improved clinical outcomes for patients with cancer.

Despite ever-growing experimental evidence for the utility of a wide range of tumour markers, only a handful are understood to be useful in clinical applications. Tumour markers are useful for screening and diagnosis of cancers, prognostication, guiding treatment pathways and post-treatment surveillance studies. The tumour makers play a significant role in cancer care and the markers included in the current treatment guidelines will be discussed in detail in this chapter. The utility of the tumour markers in the management of colorectal, breast, thyroid, hepatobiliary, pancreatic, ovarian, testicular, neuroendocrine and prostate cancer are detailed herein to provide an update on the current use of tumour markers in the clinical settings. 

Epigenetic modifications are heritable changes to gene expression without physical changes to the actual DNA sequence. The most widely studied epigenetic modification is DNA methylation, as it is influenced by aging, diet, diseases and the environment. DNA methylation involves direct chemical modification to the DNA and plays an important role in gene regulation by preventing proteins from binding to certain regions of the DNA, which causes these regions to be repressed. It is essential for normal development, cell differentiation and regulation of cellular biology. The DNA methylation landscape of each unique cell type helps to determine which genes are expressed and silenced. It is well known today that the accumulation of both genetic and epigenetic abnormalities contributes to the development of cancers. Aberrant DNA methylation is a hallmark of cancer. During cancer development and progression, the methylation landscape undergoes aberrant remodelling. Recently within cancer research, the advancements in DNA methylation mapping technologies have enabled methylation landscapes to be studied in greater detail, sparking new interest in how the methylation landscape undergoes a change in cancer and possible applications of DNA methylation. This chapter focuses on reviewing DNA methylation landscapes in normal cells and then how they are altered in cancer. It also discusses the applications of DNA methylation as cancer biomarkers.

Chromosomal abnormalities induce genomic instability and are associated with cancer hallmarks. Chromosomal abnormalities can be categorised into structural and numerical aberrations and are seen under a light microscope. Given the ease of detecting and observing such changes using karyotyping, chromosomal aberrations may be a useful diagnostic tool. For example, the discovery of the Philadelphia chromosome was a cytogenetic hallmark of chronic myeloid leukaemia and acute lymphoblastic leukaemia. Thus, this chapter explores potential aberrations which have the potential to be used as cancer markers in a clinical setting. Recurrent structural aberrations with known genetic mutations are observed in cancers of the bones, lungs, salivary glands, soft tissue, stomach, thyroid, and uterus. The association of these genetic alterations with various cancers suggests a causative role of structural aberrations in carcinogenesis and is characteristic of some cancers. Additionally, mono- and tri-somies, known as aneuploidy, are common to all cancer types, however, their roles as a cause or consequence are difficult to establish due to the sheer loss or gain of genetic material, respectively. Cancers with the most frequent trisomies, include Ewing’s sarcoma of the bone, astrocytoma of the brain, and renal adenocarcinoma. Common cancer monosomies include meningioma of the brain and ovarian adenocarcinoma. These chromosomal aberrations forge the path to a better understanding of cancer genetics. Though there are potential chromosome markers in cancer, the heterogeneity of cancer genetics makes this a challenging tool to incorporate into current oncological diagnostic guidelines. 

Cancer pathogenesis is a multistep process involving the accumulation of complex genetic and epigenetic alterations. The disease can be sporadic or familial in nature. The genes associated with much familial cancer or inherited cancer susceptible syndrome have already been identified. Thus, genetic testing for pathogenic variants of these genes could predict whether an individual has a high risk of developing cancer in their lifetime. Also, tumour DNA sequencing in patients with cancer can be used for therapy selection and to predict treatment outcomes. The recent development of high throughput sequencing enables the exploration of whole genome profiling, including mutations, structural variations, transcriptomes, splicing events, etc., in patients with cancer, thereby providing guidelines for personalized precision medicine in clinical practice. However, the translation of cancer genome sequencing information into the clinical treatment plan is highly complicated, needs multidisciplinary expert panels and is not cost-effective for mass application. Further development in sequencing analysis and data interpretation are imperative for point-of-care settings applications. This chapter outlines the clinical significance of tumour DNA testing and genomic sequencing in various cancers.

Liquid biopsies, such as tumor-relevant proteins, miRNAs, circulating tumour cells (CTC) and cell-free DNA (cfDNA), have all been shown to have promising potential to be used as cancer biomarkers. However, the sensitivity and specificity of these biomarkers are currently insufficient, prohibiting their widespread application in clinical practice. Circulating tumour DNA (ctDNA) has received a lot of attention in recent years as a potential diagnostic and prognostic tool. Since tumours release genetic material, (i. e. ctDNA) into the bloodstream before they are apparent on imaging or cause symptoms, thus, ctDNA is one of the most promising liquid biopsy biomarkers for early diagnosis, prognosis, and treatment monitoring of patients with cancer. Accordingly, extensive preclinical and clinical research support that ctDNA has the potential to be considered a novel tool in early cancer diagnosis and prognosis. Also, ctDNA analysis can reliably predict tumour growth and treatment efficacy, as well as can aid in targeted therapy. Herein, this chapter will discuss the clinical significance of ctDNA in the management of patients with cancer as a potential liquid biopsy biomarker. 

Circulating tumour cells (CTCs), as 'liquid biopsy”, has a major benefit over traditional tissue biopsy and has the potential to become a less invasive and more costeffective cancer biomarker. The presence of CTCs in the circulation indicates the presence of a tumour and the possibility of metastatic spread. Hence, the characterisation of CTCs is expected to provide crucial insights into the mechanisms of metastasis. It can also provide useful information about the future use of CTCs as a surrogate endpoint biomarker in diagnosis, prognosis, and treatment response prediction by minimizing the limitations of tissue biopsies. Also, it provides a new horizon for the development of novel targeted therapies. However, the lack of specific and effective methods is the key limitation in CTC detection and isolation in patients with cancer. Therefore, more responsive methods and approaches may be needed to improve the accuracy of CTC measurements. Herein, this book chapter will provide a current picture of CTCs as surrogate biomarkers for disease diagnosis, prognosis and predicting therapy response, along with the risk of relapse in cancers.

Cancer is one of the leading causes of death worldwide and it is becoming increasingly important to be able to efficiently identify and map the progression of cancers. The study of the diagnostic, predictive and prognostic value of protein biomarkers has become one of the main aspects at the forefront of cancer research. The diversity of various biomarkers for different cancers and their varying roles in each disease presents a continual challenge for researchers to understand, with new biomarkers still being discovered today. Understanding the role of protein biomarkers ensures patients are diagnosed with greater confidence and helps clinicians with treatment regimes. This chapter aims to discuss the clinical significance of various protein biomarkers in terms of their diagnostic, prognostic, and predictive value in the treatment of their respective cancers.

Enzymes catalyse biochemical reactions and tightly regulate biophysical and metabolic pathways to maintain cellular homeostasis. However, the unregulated activity of these enzymes results in metabolic disorders and genetic diseases, including cancer. In cancer, significant alteration of enzyme levels and/or activity can be detected during malignant transformation, thus, it can be used as a potential biomarker in clinical applications. For example, serum levels of lactate dehydrogenase (LDH), neuron-specific enolase (NSE) and thymidine kinase 1(TK1), alkaline phosphatases (ALPs), tumour M2-PK, hexokinase (HK), etc., significantly increased in patients with various cancers, such as metastatic breast cancer, intracranial germ cell tumours, ovarian serous carcinomas, oesophagus, cervical, gastrointestinal, prostate, renal cell carcinoma, head and neck and lung cancers. Also, they are associated with various clinicopathological factors, such as stage, grade, lymph node metastasis, distant metastasis, etc. In addition, overexpression of carbonic anhydrase XII (CAXII), matrix metalloproteinases (MMPs) and aldehyde dehydrogenase 1 (ALDH1), in cancer tissues, is associated with the presence of several cancers and correlated with the progression of the diseases. Therefore, screening of these enzymes at the point-of-care settings could facilitate better management of patients with cancer. This chapter summarizes the roles of cancer associated-enzymes, especially emphasizing their clinical significance in patients with various cancers. 

Glycoproteins or glycosylated proteins are carbohydrates (oligosaccharide chains or glycan’s) linked proteins and execute important functions in the biological systems, such as embryonic development, cell-to-cell recognition, adhesion, pathogen identification and immune functions. It is evident that the alteration of glycoproteins in cells are associated with a number of human diseases, including cancer, rheumatoid arthritis, inflammatory diseases as well as immunodeficiency diseases. Recent advances in modern technologies in cancer treatment are promising. However, researchers and clinicians are still searching for appropriate biomarkers for the early detection and management of patients with cancer. Altered glycoprotein levels are associated with critical events in cancer pathogenesis and progression. Also, abnormal glycosylation of protein is a common regulatory event in carcinogenesis, therefore, aberrant glycosylation could act as a promising resource in identifying a cancer biomarker for diagnosis and monitoring of the progression of patients with cancers. This chapter summarizes the major clinically approved glycoproteins utilized for screening, diagnosis, and monitoring of the treatment response of patients with cancers.

Among all the cancer biomarkers, hormones are less discussed despite having the ability to be used as potential biomarkers in the diagnosis and prognosis of various cancers. When a tissue, normally produces hormones in lesser quantity, produces a hormone in excess levels, then hormones can be used as tumour biomarkers. Sometimes it is also seen that a hormone is produced by the tissue, which is not normally associated with the secretion of that hormone. For example, calcitonin, a protein hormone produced by the thyroid gland, is reported to be increased in production in thyroid carcinoma. Another protein hormone, namely human chorionic gonadotropin (hCG), is used as a biomarker in choriocarcinoma, testicular tumors, etc. On the other hand, a lower level of testosterone hormone is found in prostate cancer, indicating its role in prostate cancer prognosis. There are other peptidase and steroid hormones, such as insulin, glucagon, estrogen and progesterone which significantly contribute to various tumours and are used as valuable biomarkers in the diagnosis and prognosis. Taken into consideration, in this chapter, we discuss the roles of multiple peptides and steroid hormones in the diagnosis and prognosis of various cancer types. 

Despite the fact that the mortality rate of many types of cancer has decreased in the last decades, cancer remains one of the most challenging diseases in the world. The number of newly diagnosed cases with advanced stages in different types of cancer is still high because available tests are not efficient enough to be used for screening. In addition, the available diagnostic tests failed to diagnose certain types of cancer until late presentation. Furthermore, therapeutic agents currently in clinical use to treat a certain type of malignant tumours still show a high rate of resistance in some patients. Many types of available cancer biomarkers failed to manage and resolve this problem because of the lack of both sensitivity and specificity of these markers. Advanced researches in epigenetics highlight the importance of certain non-coding genes in diagnosing and follow-up of patients with different types of cancer. One of these substances is microRNAs (miRNAs) which showed high sensitivity and specificity as cancer biomarkers. miRNAs are highly stable and expressed in different types of human body samples; some of them are tissue specific. These features make them available as cancer biomarkers, and they are started to be in clinical use recently. 

According to the miRBase (v 22.1), released on October 2018, there are more than 1900 identified human microRNA mature sequences. MicroRNAs (aka miRNAs or miRs) are a class of short non-coding RNA sequences, which have been detected within the cells or in body fluids. They act as gene expression regulators and intervene in numerous physiologic and development processes. They posttranscriptionally/ translationally regulate expression of some proteins by forming miRNA-induced silencing complex (mRISC) by binding to 3’-UTR regions of the target messenger RNA to inhibit the protein synthesis. It has been noted that up- and down-regulation of miRs are associated with the pathogenesis of several types of human cancers since their target proteins are tumor-suppressive or oncogenic ones. This chapter will present a general summary of miRNA biogenesis, their link to cancer, and biological methods for their detection. Thanks to their ease of use and high sensitivity, electrochemical and optical techniques were used to detect miRNAs with or without the assistance of amplification methods. We will review the state-of-the-art electrochemical and optical methods for their detection, emphasizing the progress achieved in the last five years (2015-2020). Finally, we will present the main advantages, challenges, and future prospects for future research on detecting miRNAs for clinical diagnosis or prognosis in cancers.

Biosensors are common analytical devices, capable of sensing a myriad of biological analytes, including cancer biomarkers. Although biosensors have different transducer types, electrochemical biosensors provide fast analysis time, high sensitivity, and the ability to perform complex measurements such as multiplexed analysis or screening tests for early diagnosis and prognosis of cancer. This chapter describes the background and theory of electrochemical sensors and introduces the main readout techniques. Innovative electrochemical biosensing strategies for analysis and quantification of important early cancer biomarkers, which include circulating nucleic acids (e.g., circulating tumour DNA, gene mutations, and microRNA) proteins, circulating tumour cells, and extracellular vesicles are discussed with the recent developments to provide an overview of the possible academic and clinical approaches