Current Cancer Biomarkers

By Bentham Science Publishers

Current Cancer Biomarkers is a comprehensive review on the status of biological markers for various types of cancer. It aims to update readers on current developments on the subject. The contents are divided into 5 sections covering a wide range of biomarkers and their diagnostic applications. The range of tumour biomarkers referenced here gives insights into molecular mechanisms behind cancer, including initiation, development, progression, prognosis, response to the therapeutic modalities, recurrence, and point-of-care application to detect cancer.

Key features
- Introduction of the basic features of cancer markers
- Comprehensive and updated coverage of potential and effective biomarkers including genomic, epigenomic, transcriptomic, proteomic, cellular and morphologic factors
- Information on biomarkers in many types of cancers including breast cancer, colorectal cancer, skin cancer, leukemia, liver cancer and prostate cancer
- Applications of biomarkers in cancer diagnosis
- Structured contents with easy-to-understand sections and headings
- References for advanced readers

The updated information about different aspects of cancer markers in the experimental and clinical setting will enrich the reader's understanding of the disease. The information serves as a resource to help in better management of cancer patients and understanding cancer biology when planning medical research projects. The book is intended as a reference for a diverse audience: biomedical science students, medical students, academics, researchers, clinicians and multidisciplinary teams involved in cancer management and research.

• Language: English
• Publisher: Bentham Science Publishers
• Release date: Mar 17, 2008
• ISBN: 9789815079364

Book preview

Part 1: Introduction and Clinically Used Biomarker

Introduction: Current Status and Future Advances in Cancer Biomarkers

Farhadul Islam¹, *

¹ Department of Biochemistry and Molecular Biology, University of Rajshahi, Rajshahi-6205, Bangladesh

Abstract

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.

Keywords: Biomarkers, Cancer markers, Cancer management, Cancer burden, Cell-free DNA, Circulating tumour DNA, Circulating tumour cells, Classical cancer markers, Clinical application, Diagnostic markers, Drug toxicity, Liquid biopsy, Non-coding RNAs, Predictive markers, Prognostic markers, Personalized treatment, Precise medication, Tumour-derived exosomes, Tumor-derived extracellular vesicles.

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* Corresponding author Farhadul Islam: Department of Biochemistry and Molecular Biology, University of Rajshahi, Rajshahi-6205, Bangladesh; E-mail: [e-mail]

INTRODUCTION

Cancer, a group of diseases, can affect any part of the body, involving uncontrolled growth and proliferation of cells caused by different factors, resulting in extreme molecular and cellular heterogeneity in different and even in a single cancer [1]. However, one defining feature of cancer is the rapid generation of abnormal cells that can grow beyond their usual boundaries and

have the potential of local invasion and distance metastasis- migrating to the other parts of the body. The latter, metastases, is the primary reason for cancer-related mortality in patients with cancers.

Cancer is a major health burden and a leading cause of death worldwide. In 2020, cancer accounted for about ten million deaths, with 19.3 million cases globally [2]. According to GLOBOCAN 2020, 1 in 5 people develop cancer during their lifetime, while 1 in 8 men and 1 in 11 women die from the disease globally [3]. The burden of cancer can be reduced (30 to 50%) by avoiding risk factors (e.g. tobacco and alcohol use, unhealthy diet, physical inactivity, air pollution, other non-communicable diseases etc.) and by using existing evidence-based prevention strategies. In addition, the cancer burden can also be reduced by early detection, proper care and appropriate treatment modalities [4]. Many cancers have a high chance of cure if diagnosed early in the disease.

Early detection and diagnosis of cancers, especially asymptomatic cases, are challenging and effective markers or methods yet to be established for point-of-care applications. Thus, there is an urgent need to develop effective biomarkers or panel of biomarkers (cancer biomarkers), which can diagnose patients with cancer at early stage with high specificity and sensitivity. Also, sensitive and specific biomarkers for stratification of stages, disease progression and therapy response could improve the clinical outcome of patients with various cancers. A biomarker or biological marker is a measurable indicator of biological condition and/or state using blood, urine, stool or soft tissues [5]. Measurement of a biomarker provides information on normal biological/cellular processes, pathogenic processes or pharmacologic responses to therapy. Thus, in principle, cancer or tumour biomarker is a biomolecule or part of biomolecules found in blood, urine, stool or body tissues, which elevated in the presence of cancer in biological samples. These biomarkers can be generated directly by a cancer cell or by a non-cancer cell in presence of cancer. Most of the cancer biomarkers can be categorized as tumour-specific antigens or tumour-associated antigens. They could be either (i) products of mutated oncogenes, (ii) products of tumour suppressor genes, (iii) products of other mutated genes, including (a) overexpressed or abnormally expressed cellular proteins or protein fragments, (b) tumour antigens produced by oncogenic viruses, (c) oncofetal antigens, (d) altered cell surface glycoproteins and glycolipids and (e) cell-type specific differentiation antigens, and (iv) altered or aberrant genetic and epigenetic make-up in cancer cells. Thus, a biomarker can be genetic materials, such as DNA, RNAs, including non-coding RNAs, or their products, i.e. proteins or peptides or even epigenetic changes, such as DNA-methylation. However, an ideal cancer biomarker should have the following criteria for effective use in clinical applications [6].

A. Produced in the presence of cancer (significantly elevated levels).

B. Associated with the cancer burden and provide sufficient lead time (length of time between the disease detection and its usual clinical presentation and diagnosis).

C. Significantly higher levels in blood, urine, stools or other biological samples in patients with cancer than in healthy individuals, especially at early or preclinical stages of patients.

D. Highly sensitive and specific for cancer types, preferably one type of cancer.

E. Easy, cost-effective, less labour intensive and able to measure in small quantities in point-of-care settings.

Classical Cancer Biomarker

A cancer biomarker can be used for screening, diagnosis, monitoring disease progression, therapy response and disease recurrence/relapse [7], therefore, giving the information of the disease status in particular patients, which in turn can facilitate the personalized cancer management in patients. Thus, cancer biomarkers can be classified into three broad categories, (i) diagnostic, (ii) prognostic and (iii) predictive biomarkers. However, a biomarker can be used for more than one clinical applications, thereby can fall into more than one of these groups.

Diagnostic Cancer Biomarkers

As mentioned earlier that early detection of cancer can significantly reduce the cancer burden, thereby alleviating economic and social costs associated with cancer. Early detection of cancer allows better response to the treatment, resulting in higher survival rates and less morbidity, along with the lower cost of management [8]. Therefore, a significant improvement can be made in patients with cancers by detecting them at earlier stages, especially at the asymptomatic stages and avoiding delays in proper care.

Early cancer detection can be carried out by screening of mass population using appropriate biomarker tests with the aim to identify individuals with findings indicative of specific cancer or pre-cancer at the asymptomatic phase. Identification of abnormalities during screening suggests further tests to diagnose the disease. The screening test must be inexpensive and safe enough to be used by mass populations and should be very highly sensitive and specific to avoid too many false positives in tested populations [9]. The screening programs for early detection are effective for some cancer types but not all cancer types. Also, the screening programs are far more complex and resource-intensive, requiring special equipment and resource personnel. The most widely used screening methods for early detection cancer are human papilloma virus (HPV), Papanicolaou (Pap) cytology and visual inspection with acetic acid (VIA) testing for cervical cancer, mammography screening for breast cancer. Also, human choriogonadotrophin can be used for germ cell tumours and gestational trophoblastic disease, α-fetoprotein can be used for hepatic and testicular carcinomas screening [9, 10]. However, an effective biomarker test for mass population screening and early cancer detection in clinical settings is yet to be established and poised a greatest challenge in cancer research and management.

On the contrary, a diagnostic cancer biomarker should narrow down the diagnosis and identify specific individual patients in clinical settings. Thus, a diagnostic biomarker test should be prescribed to individuals who have already developed symptoms of specific cancer types. However, there is no well-established biomarker test recommended in clinical practice for cancer diagnosis [6, 11]. Although, a number of well-known markers are widely used as a facilitator in the diagnosis and/or stratification of the cancers’ pathological state. Since, there is no specific and recommended tumour biomarker for diagnosis, they should not be used for cancer diagnostic purposes, while they can be used to monitor or screen certain cancer types or certain cancer cases [12, 13]. Inappropriate and over-investigation would be the results of these biomarker tests if applied without understanding their utility in patient care.

Prognostic Cancer Biomarkers

Prognostic markers are biomarkers used to measure the progression of the disease using patients’ biological samples. They are biomolecules, factors or biological characteristics that can be measured objectively and evaluated to predict the outcome of a disease or response to a therapeutic intervention among individuals with the same trait [14]. Thus, they provide information about the patient's overall outcome irrespective of therapeutic intervention.

The clinically useful prognostic biomarkers are used to stratify the patients into groups, thereby guiding them toward personalized medication. In cancer, the widely used traditional prognostic markers include tumour size, grade, lymph node metastasis, stage and distance metastasis. Larger tumour size, higher grade, advanced staging and presence of metastasis are associated with poor prognosis in patients with cancer [15]. In addition, cancer-specific prognostic markers also used in patient with various cancers. For example, estrogen, progesterone and HER2 levels are used as prognostic markers for patients with breast cancer [16].

Additionally, advances in molecular techniques in genomics, epigenetics and proteomics research, such as microarray, and deep or high throughput sequencing, have provided better opportunities to identify new biomarkers for cancer prognosis. These new generations of prognostic markers can be genetic (i.e., DAN), epigenetic (e.g. methylation, non-coding RNAs), signalling pathways, proteins or protein fragments and metabolic molecules [17, 18]. The newly developed biomarkers can provide information that can facilitate the oncologist to guide personalised management of patients with cancer.

Predictive Cancer Biomarkers

Predictive biomarkers can be used to predict the likelihood benefit of specific therapy and optimize ideal treatment for clinical outcomes [19]. In oncology, predictive biomarkers assess the probable response of the tumour to the drug, thereby introducing a level of personalized treatment regimen in patients. Thus, an effective predictive biomarker could reduce the cost in considerable amounts as the therapy or drugs would be used only in patients likely get benefit from the treatment. However, till now, only a small number of biomarkers such as K-ras mutations, ER, PR and HER2/neu levels, BCR-ABL fusion protein, c-Kit mutations and EGFR1 mutations etc., have predictive clinical utility for patients with cancer [14, 20]. For example, BCR-ABL fusion protein and EGFR1 mutations are used as predictive biomarkers for patients with chronic myeloid leukaemia and non-small cell lung carcinomas, respectively in clinical care [14]. Also, predictive biomarkers (K-ras mutations) in metastatic colorectal cancer can evaluate and improve patients’ survival rates [19]. In addition, a number of predictive biomarkers are gaining clinical acceptance as their objective measurements can give clinical response to the drug; patients only expressing the specific marker will response to the specific drug or will have higher degree of response while patients without the marker won’t exhibit significant drug response [21]. Thus, in individual case by case scenario, predictive markers can differentiate the patients as responder from non-responder to guide the choice of anticancer therapy, resulting in sparing the patients from unnecessary toxicity and side effects of the regimen, thereby improving cancer care.

Future Cancer Biomarkers

The discovery and development of traditional cancer biomarkers could improve the survival rates and quality of life of patients, thereby having significant impacts on the better management of patients with cancers. However, research in the field of classical/traditional cancer biomarkers development is currently discouraging, as most of the newly identified cancer biomarkers are abandoned or fail clinical validation due to poorer analytical performance, resulting in no clinical utility in practical applications [22]. Nonetheless, the recent advancement of sequencing technologies, such as next-generation sequencing, high-throughput or deep sequencing etc., improved analytical platforms and/or methods to detect and analyse single cell or cells cluster allows to identify and develop new generation of cancer biomarkers, popularly known as liquid biopsy, with the potential of clinical utility for patients with cancers [23]. These liquid biopsies have been receiving enormous attention in recent years as easy, rapid and non-invasive tools for cancer screening, diagnosis, prognosis and prediction of therapeutic intervention in cancer patients [24]. The potential candidate for effective liquid biopsies, includes but not limited to, circulating tumour cells (CTCs), metastatic-CTCs, circular tumour-DNA (ctDNA), cell free-DNA (cfDNA), non-coding RNAs (e.g. microRNA, long non-coding RNA, circular RNAs etc.), cancer epigenetics, tumour derived exosomes (TEX), tumour derive extracellular vesicles (TD-EVs) etc., exhibiting promising clinical utility in clinical applications.

CTCs are the disseminated cancer cells found in the peripheral blood in solid malignancies and their presence in blood and quantity associated with the prognosis of various cancers, including breast, colorectal, head and neck, lung, oesophageal, pancreatic, gastric etc., cancers [25]. In addition, molecular and functional characterization of CTCs provide personalized information about the patients, which in turn can dictate the diagnosis, prognosis and prediction of therapy. Profiling of CTCs can also have the potential to be used for predicting micrometastasis, monitoring progression and stratification of cancer [25]. However, analytical grade platforms and /or methodologies for the detection and characterization of CTCs yet to be established. Thus, standardised methods or technologies must be developed to detect and analyse CTCs for their clinical applications.

ctDNA is a tumour-derived DNA fragment found in the peripherals blood, originated only from tumour cells and CTCs. As ctDNA reflect the entire cancer genome, it has the potential of clinical utility as liquid biopsy by drawing blood at various time points to monitor disease progression [26]. Higher levels of ctDNA associated with larger tumour size and ctDNA harbour similar cancer-associated mutations in genomic DNA of patients with cancer, indicating that ctDNA can be used as a cancer detection, prognostic and treatment follow up biomarker [27, 28]. In addition, ctDNA can predict the presence of tumour recurrence by detecting minimal residual disease, whereas conventional imaging methods, such as CT, PET or MRI scan may unable to detect presence of disease after tumour resection. However, the clinical utility of ctDNA for primary cancer screening is limited by the sensitivity of the current technologies to detect low levels of ctDNA presence in patients with small tumours at early stages of the disease [27]. Therefore, clinical application of ctDNA is would be established by developing standardised methods for ctDNA processing and analysis along with the standardization of sample collection, downstream processing such as DNA extraction, amplification, quantification and validation must need to be established for routine analysis in clinical settings.

cfDNA is the freely circulating DNA fragments with a predominant 166bp length, found in the bloodstream, however, not necessarily of tumour origin [29]. The length of fragmentation is an indication of apoptotic fragmentation and altered cfDNA fragmentation is detected in cancer patients [29, 30]. As cfDNA is possibly derived from necrotic, apoptotic and living cells, their profiling and characterization of such epigenetic alterations have potential clinical applications for early detection, prognosis and prediction of therapy response [31].

Non-coding RNAs, including microRNAs (miRNAs), long non-coding RNAs (lncRNA), etc., are RNA molecules that do not translate into a specific protein, however, they regulate the expression and functionality of their targets, either at post-transcriptional or post-translational levels [32]. Since they regulate the expression of tumour suppressors and oncogenes, their alterations in cancer are associated with cancer initiation and disease progression [33]. A number of noncoding RNAs, such as miRNA-1, miRNA-34b, miRNA-miRNA-186, HOTAIR, GAS5, and SNORD50, etc., are associated with prognosis and diagnosis of various cancers [33-35]. Thus, profiling and validation of non-coding RNAs in cancer could have potential biomarkers implication for cancer diagnosis, prognosis and prediction of clinical outcome inpatients with cancer.

Exosomes are nanovesicles derived from all types of cells carrying information (e.g. mRNA, miRNA, circular RNA and proteins) originating from the parental cells. Tumour-derived exosomes (TEXs) carry endogenous cargos containing molecules that reflect the pathological status of cancer, thus, providing their potential to be used as novel non-invasive cancer diagnostics, prognostics and monitoring biomarkers [36, 37]. Also, tumour-derived extracellular vesicles (TD-EVs) can carry multiple cargoes containing DNA, RNAs, and proteins during distant metastasis. Paracrine signalling mediated by TD-EVs between adjacent cancer cells allows crosstalk, which in turn modulates the tumour microenvironment in favour of becoming a premetastatic niche [38]. Hence, TD-EVs could be a potential biomarker for cancer development and metastasis. Therefore, analysis of TD-EVs and TEXs derived genetic materials and proteomics have widespread potential use in cancer diagnosis and treatment. However, established and standardized methods for accurate and sensitive detection and isolation need to be develop for their clinical applications.

CONCLUDING REMARKS

The trial and error approach to cancer treatment and management is largely empirical, costly, and more frequently ineffective, resulting in poor clinical outcomes. The traditional ‘one size fits all’ strategy lead some patients (patients with aggressive tumour load) under treatment, whereas to other patients (patients with indolent disease) over treatments, thereby generating drug-associated toxicity. On the other hand, recent personalised or individualized strategies based on molecular and functional characterization of each cancer patient would provide precise information for the better management of each case. Personalized therapy provides the right drug to the right patient at the right time with the correct dose and schedule. This could provide an optimum clinical outcome for patients with cancer, however, without reliable, robust, validated, sensitive, specific and accurate cancer biomarkers, personalized precise medication would not be successful in practical applications.

CONSENT FOR PUBLICATION

Not applicable.

CONFLICT OF INTEREST

The author declares no conflict of interest, financial or otherwise.

ACKNKOWLEDGEMENT

The author is thankful to the University of Rajshahi for providing the technical support.

REFERENCES

Tumour Markers in Clinical Use

Sujani M. K. Gamage¹, ², *, Chamath D. Ranaweera³, ⁴, Tracie T. Cheng¹, Sharmin Aktar¹, ⁵, Vinod Gopalan¹, Farhadul Islam⁶

¹ School of Medicine, Griffith University, Gold Coast, QLD, Australia

² Faculty of Medicine, University of Peradeniya, Galaha Rd, 20400, Sri Lanka

³ National Cancer Institute of Sri Lanka, Maharagama, Sri Lanka

⁴ Sunshine Coast Hospital and Health Service, QLD, Australia

⁵ Department of Biochemistry and Molecular Biology, Mawlana Bhashani Science and Technology University, Tangail-1902, Bangladesh

⁶ Department of Biochemistry and Molecular Biology, University of Rajshahi, Rajshahi-6205, Bangladesh

Abstract

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.

Keywords: Alpha-fetoprotein (AFP), Breast cancer, Calcitonin cancer, Cancer treatment, Carcinoembryonic antigen (CEA), Chromogranin A, Colorectal cancer, Current guidelines in cancer care, CA 125, CA 19.9, Follow-up in cancer care, Hepatobiliary cancer, Neuroendocrine tumours, Ovarian cancer, Pancreatic cancer, Prostate cancer, Prostate-specific antigen (PSA), Screening, Surveillance, Testicular cancer, Thyroglobulin (Tg), Thyroid cancer, Tumour markers.

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* Corresponding author Sujani M. K. Gamage: School of Medicine, Griffith University, Gold Coast, QLD, Australia; E-mail: [e-mail]

INTRODUCTION

Tumour marker is a substance (commonly a protein, enzyme or hormone) that is present or produced either by tumour cell or by other cells in the body due to the effects of cancer, which can be detectable in body fluids or tissue and provides

valuable information about the aggressiveness of cancer, potential treatment modalities as well as disease and treatment outcomes. Also, they can either be produced within the cancer cells or by the non-cancerous cells as a result of the metabolic alterations caused by cancer [1]. Genetic alterations are also being considered tumour markers, especially for screening purposes. Theoretically, an ideal tumour marker should have the following characteristics: (i) having a high degree of specificity to the particular tumour; (ii) possessing high sensitivity to rule out possible false positives; (iii) allowing a sufficient time frame (lead time) to alter the natural course of the disease; (iv) detectable levels being reliably correlated with the tumour burden, while closely reflecting tumour progression; (v) having a short half-life, permitting serial measurements and (vi) being affordable for patients. Unfortunately, such an ideal tumour marker does not exist, and the available markers have their advantages and limitations [2].

Tumour markers are particularly important in assessing treatment response and residual disease, surveillance and follow-up. Following treatment, normalization of tumour markers usually denotes adequate cancer resection/ treatment. Normalized tumour marker levels with radiological evidence of persistent disease may indicate that the tumour is non-viable. There may be a transient increase in tumour marker levels following effective treatment, secondary to cell lysis. Therefore, an increase in tumour marker levels on its own does not signify treatment failure. However, increasing tumour markers in a clinically deteriorating patient may indicate treatment failure or recurrence, warranting further work-up [3].

Though there are experimental evidence for the utility of a wide range of tumour markers for each cancer, only a handful are used in the actual clinical setting (Table 1). Selected tumour markers, which are routinely used in the clinical setup and are important in the diagnosis and management of cancers, will be discussed in detail in this chapter.

Markers for Colorectal Cancer

Colorectal cancer (CRC) is the third most common cancer worldwide, affecting mostly the population in developed countries [4]. However, the prognosis of patients with CRC depends mainly on the cancer staging at the time of presentation. Tumour markers have particular importance in the diagnosis of disease and determination of prognosis of patients with CRC. Carcinoembryonic antigen (CEA) is the most used tumour marker in clinical practice for CRC. In addition, tissue polypeptide-specific antigen (TPS), carbohydrate antigen (CA 19.9), hematopoietic growth factors (HGF-s) and tumour-associated glycoprotein-72 (TAG-72) are promising as potential tumour markers in CRC [5, 6]. Macrophage-colony stimulating factor (M-CSF), granulocyte-macrophage-colony stimulating factor (GM-CSF), Cathepsin D, interleukin-3, interleukin-6 and enzymes, such as Alcohol Dehydrogenase and Lysosomal Exoglycosidases, are also recognised as potential CRC related tumour markers [7-10]. However, these are still not widely used in clinical practice. Since most cancer-related deaths are due to metastasis, investigations on circulating tumour cells (CTCs) will be promising with respect to gaining information on the prognosis and treatment response of patients with CRC [11-13]. Nevertheless, currently, only CEA is considered a reliable marker for CRC in clinical practice.

Diagnosis

CEA is an oncofetal antigen present in most epithelial tumours and is the most versatile and frequently used tumour marker in clinical settings [6]. Relative cost-effectiveness has warranted its use in routine clinical practice. However, serum CEA levels are elevated in only 17-47% of patients with CRC [14-16]. CEA can be elevated in many benign conditions, including benign liver and kidney disease, pancreatitis, inflammatory bowel disease, obstructive pulmonary disease and other malignancies including gastric, oesophageal, pancreatic, lung, breast and mesotheliomas. Levels may also be higher than the reference range in chronic smokers, and the cut-off point for the upper normal value is twice as for a non-smoker [17, 18]. Therefore, CEA is not used in isolation to diagnose CRC due to its lack of sensitivity and specificity. However, the presence of a high concentration of CEA can be useful in circumstances in which there is a high clinical probability of cancer, and the patient is not fit enough to undergo invasive investigations. Also, markedly raised serum CEA levels (>40µg/L) are usually indicative of metastatic disease [18].

Prediction of Prognosis

Although pathological staging of CRC is the most reliable prognostic predictor, serum CEA levels are routinely performed to reinforce decision-making. High CEA level during the preoperative period is correlated with poor prognosis [15, 18].

Follow up

Several studies have confirmed that intense post-treatment surveillance improves overall survival by detecting treatable metastasis [19, 20]. Along with imaging and endoscopic surveillance, serum CEA is a reliable tumour marker for the detection of recurrences in CRC patients. Up to 50% of patients who undergo curative resection for CRC can develop liver metastasis within 5 years. Resection of resectable liver metastasis is the only curative treatment apart from a liver transplant. Early detection of resectable liver metastasis improves the outcome significantly, and serial monitoring of CEA is extremely useful in that context. Similarly, the patients who develop metastasis are treatable with chemotherapy [21]. According to the National Comprehensive Cancer Network (NCCN) Guidelines, postoperative surveillance of CRC patients with pathological stages II, III and IV should include monitoring serum CEA levels every 3-6 months for 2 years, followed by 6 monthly tests for a total of 5 years. If serial CEA elevation is detected, the patient should be considered for subsequent investigations and treatment for metastasis [1]. Due to clonal changes in cancer cells, tumours secreting CEA at the beginning of the disease may develop metastatic disease, which does not secrete CEA. Therefore, a normal CEA level does not rule out the possibility of tumour recurrence or metastatic disease. Similarly, tumours that do not secrete CEA, in the beginning, may start producing it later due to clonal change, which is the rationale for monitoring those patient’s CEA levels following curative intent treatment.

Markers for Breast Cancer

Breast cancer is the second most common cancer worldwide and the fifth cause for cancer-related death [22]. Early detection is of utmost importance, and it is mainly dependent on the clinical parameters. Although when positive, tumour markers provide a cost-effective and less invasive way of monitoring disease progression and treatment response, the utility of most tumour markers is questioned in the clinical setting due to the low sensitivity at the early stages of the disease [23]. A list of tumour markers related to breast cancer, which have clinical relevance, has been highlighted by the American Society of Clinical Oncology. They are CA 15-3, CA 27.29, CEA, Estrogen receptor (ER), Progesterone receptor (PR), Plasminogen activator inhibitor 1 (PAI-1), Human epidermal growth factor receptor 2 (HER2) and Urokinase plasminogen activator (uPA) [24].

However, the only tumour marker of clinical significance in breast cancer is CA15-3, which is mostly used to monitor disease in clinical settings. It is high molecular weight mucin, a carbohydrate-containing protein antigen. The gene responsible for CA15-3 is MUC1, and it is highly expressed in breast malignancies, making it a reliable marker for the assessment of prognosis [25]. However, the use of CA15-3 for screening is limited because it may be elevated in other malignancies such as ovarian, lung, pancreatic, and colon cancer and in benign conditions, including benign liver and breast diseases [26]. Therefore, tumour markers are not recommended for screening for breast cancer. CA15-3 is a reliable marker of prognosis and treatment efficacy as it has been observed that its serum concentration increases with the stage and size of cancer [27]. European Group on Tumour Markers recommends serial monitoring of CEA and CA15-3 for early detection of recurrence, but it is not included in the standard post-treatment follow-up in guidelines NCCN guidelines. If measured, a 25% rise from the previous value is considered to be significant. To assess the chemotherapy response, CA 15-3 can be measured before every chemotherapy cycle. A reduction below 50% from the previous value is considered a satisfactory response [28].

In summary, none of the current clinical guidelines recommends the routine use of tumour markers in decision-making in breast cancer treatment.

Markers for Thyroid Cancer

Thyroid cancer is becoming increasingly common, especially among females. Differentiated thyroid cancers (DTC), which include Papillary, Follicular and Hurthle cell cancers, are by far the commonest, followed by Medullary and Anaplastic cancers. Thyroid tissue produces Thyroglobulin (Tg) as a precursor of active T3 and T4 hormones [29]. The serum Tg levels are proportional to the volume of active thyroid tissue. Therefore, it can be used to assess the cancer burden of DTC at presentation, adequacy of surgical clearance and monitor recurrences and treatment response [30].

Calcitonin is a hormone, which plays an important role in calcium homeostasis, is produced by parafollicular cells of the thyroid gland and is important as a tumour marker in medullary carcinoma.

Importance of Thyroglobulin in Differentiated Thyroid Cancer (DTC)

Surveillance after Thyroidectomy

Thyroglobulin is a useful marker for differentiated thyroid cancer. The definitive treatment modality for DTC is the surgical removal of the affected lobe (hemithyroidectomy) or the whole gland (total thyroidectomy), usually followed by radioactive iodine ablation of any residual thyroid tissue. It is not uncommon to leave some thyroid tissue behind, inadvertently or deliberately, during a total thyroidectomy due to various technical reasons. This residual thyroid tissue, if survived, may continue to produce Tg secondary to high TSH levels (lack of feedback inhibition). Therefore, measurement of serum Tg level is important in identifying residual thyroid tissue or recurrent disease [29]. Thus, serum Tg levels are routinely measured following total thyroidectomy (TT) as a component of the post-surgical evaluation to identify the residual, recurrent or metastatic disease [1, 29]. Serum Tg levels should be lower than the reference value of the index laboratory, following complete excision/ablation of thyroid tissue and should remain low if treatment is complete. The sensitivity of Tg measurement can be improved by either increasing the TSH value for >30 mIU/L by withholding thyroxin treatment or administering recombinant TSH. In the patient who had hemithyroidectomy or TT not followed by radioactive Iodine treatment, the interpretation of serum Tg values is less reliable due to the inability to differentiate between tumour and thyroid remnant, though the rising trend of Tg may be of clinical significance. Patients with persistently elevated Tg levels or upwardly trending Tg levels should be further evaluated for recurrence or metastatic disease, usually with Radio Iodine whole-body scan and cross-sectional imaging [31]. Nevertheless, 10-25% of patients develop antibodies against Tg (Anti-Tg antibodies), which can interfere with Tg measurement-based follow-up. Therefore, Thyroglobulin antibody (anti-Tg antibody) levels should also be evaluated along with Tg levels to exclude false-negative results secondary to the development of anti-Tg antibodies [29].

Determination of the Requirement of Radioactive Iodine Therapy

Thyroglobulin levels are useful in determining if radioactive iodine (RAI) treatment is required following thyroidectomy. In cases where there is no gross residual disease in the neck, typically RAI therapy is not required if all of the following conditions are met: the cancer is a classic papillary thyroid carcinoma, the largest primary tumour is less than 2cm in size, cancer is intrathyroidal, unifocal or multifocal with all foci are 1cm or less in size, negative post-operative ultrasound and a post-operative unstimulated thyroglobulin level of less than 1ng/ml confirmed 6-12 weeks following total thyroidectomy along with undetectable anti-Tg antibodies [1]. RAI should be selectively recommended if post-operative unstimulated Tg level is less than 5-10ng/ml measured 6-12 weeks following total thyroidectomy. If post-operative unstimulated Tg is more than 5-10ng/ml RAI treatment is recommended. However, care must be taken to exclude any normal thyroid remnant or gross residual disease by cross-sectional imaging such as computed tomography (CT) and magnetic resonance imaging (MRI) neck.

Importance of Calcitonin in Medullary Thyroid Carcinoma (MTC)

As mentioned earlier, MTC originates from parafollicular cells of the thyroid gland, hence it secretes excessive amounts of Calcitonin. Serum Calcitonin and CEA, to a lesser extent, are used as tumour markers in diagnosis, prognostication, assessment of treatment response and detection of recurrence/ residual disease in patients with MTC. Controversy exists on routine testing of Calcitonin levels in the evaluation of thyroid nodules and none of the guidelines recommends it. Using Calcitonin and CEA as a screening test in the setting of inherited MTC is abandoned due to lack of sensitivity. Calcitonin stimulation tests (with Pentagastrin or Calcium) can be used to increase the positive predictive value [31].

Baseline Calcitonin and CEA levels should be checked in all diagnosed patients with MTC before surgical treatment. A level >400 ng/L predicts an increased risk of metastatic disease, especially in the presence of nodal disease, and cross-sectional imaging for staging is indicated. Lymph node (LN) metastasis is common in MTC, and LN clearance is an important component of curative-intent treatment. Calcitonin levels can be used to guide the extent of LN dissection as a biochemical cure can be achieved in >50% of patients with <1000 ng/L of calcitonin, if subjected to bilateral neck prophylactic LN dissection [31].

Serum Calcitonin and CEA levels should be checked in all patients following surgery, and it’s not uncommon to have persistently elevated serum levels post-surgically. Doubling time for these markers can be used to get a more accurate picture of this group of patients. Further evaluation for recurrent or metastatic disease is required, especially if Calcitonin and CEA values are trending upward. Surgery is the only hope of achieving a cure for recurrent MTC, which emphasizes the importance of regular measurement of CEA and Calcitonin. However, there is a subgroup of people who have persistently elevated Calcitonin levels, yet are asymptomatic and imaging negative for recurrence or metastasis [31]. These patients do not require further treatment and can be followed up safely.

Marker for Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) is associated with chronic Hepatitis B and C infections, Aflatoxin B1 fungal toxin ingestion, alcoholic liver cirrhosis, autoimmune hepatitis etc. and HCC is the sixth most prevalent cancer in the world [32]. A number of tumour markers are being investigated for their potential applications in screening, diagnosis and predicting the prognosis of HCC. Out of them, only AFP (alpha-fetoprotein) is of current clinical relevance.

Screening

Patients with cirrhosis due to any reason and patients with hepatitis B infection (even without cirrhosis) are identified as being at high risk of developing HCC [1]. These patients should be screened for HCC by Ultrasound scanning (USS) and measurement of AFP levels. Even though AFP measurement cannot replace USS assessment, high or rising AFP levels are considered a prompt for CT or MRI scanning, regardless of USS results. Positive AFP levels or liver nodule/s of size 10mm or more in USS warrants further investigations to diagnose or exclude HCC [1]. If AFP and USS are negative, it is recommended to monitor with AFP and USS for another 6 months. If liver nodule/s less than 10mm in size are detected in USS, the patient should be followed up with a repeat USS and AFP levels in 3-6 months [1]. There is compelling evidence that screening with AFP and USS enables the detection of smaller HCCs at an earlier stage, thereby increasing the curability [33, 34].

Staging and Further Assessment

In patients with confirmed HCCs, comorbidity and liver reserve are assessed, and staging is determined by multidisciplinary evaluation. Alfa fetoprotein measurement is important for this staging process, along with evaluation of levels of bilirubin, liver transaminases, alkaline phosphatase, PT/INR, blood urea nitrogen (BUN), albumin, creatinine, platelets and chest X-ray etc [1].

Surveillance in HCC

Following definitive treatment for HCC, surveillance is done by monitoring AFP levels and imaging (multiphasic abdominopelvic MRI/ multiphasic CT) every 3-6 months during the first 2 years following surgery and 6 monthly thereafter [1]. Following adequate tumour resection, AFP levels should decline with a half-life of 3.5-4 days. Inadequate resection can be suspected when the half-life is longer or when AFP levels are not normalized following resection [34].

Markers for Gall Bladder and Cholangiocarcinoma

Gall bladder and biliary tract cancers are relatively rare, with worldwide age-standardized incidence rates of 2-3 per 100,000 population [35]. Gall bladder carcinomas are fatal, with only 10% of patients