Plasma and urine biomarkers in acute viral hepatitis E

Dysregulated metabolites and lipids in serum of patients with acute hepatitis E: A longitudinal study

Hepatitis E is a disease associated with acute inflammation of the liver. It is related to several dysregulated metabolic pathways and alterations in the concentration of several metabolites. However, longitudinal analysis of the alterations in metabolites and lipids is generally lacking. This study investigated the changes in levels of metabolites and lipids over time in sera from men with acute hepatitis E compared to healthy controls similar in age and gender. Untargeted measurement of levels of various metabolites and lipids was done using mass spectrometry on 65 sera sequentially sampled from 14 patients with acute hepatitis E and 25 serum samples from five controls. Temporal changes in intensities of metabolites and lipids were determined over different times at 3-day periods for the hepatitis E virus (HEV) group. In carbohydrate metabolism, glucose levels, fructose 1-6-bisphosphate and ribulose-5-phosphate were increased in the HEV-infected persons compared to the healthy controls. HEV infection is significantly associated with decreased levels of inosine, guanosine, adenosine and urate in purine metabolism and thymine, uracil and β-aminoisobutyrate in pyrimidine metabolism. Glutamate, alanine and valine levels were significantly lower in the HEV group than in healthy individuals. Homogentisate of tyrosine metabolism and cystathionine of serine metabolism were increased, whereas kynurenate of tryptophan metabolism decreased in the HEV group. Metabolites of the bile acid biosynthesis, urea cycle (arginine and citrulline) and ammonia recycling (urocanate) were significantly altered. Co-enzymes, pantothenate and pyridoxal, and co-factors, lipoamide and FAD, were elevated in the HEV group. The acylcarnitines, sphingomyelins, phosphatidylcholine (PC), phosphatidylethanolamine (PE), lysoPC and lysoPE tended to be lower in the HEV group. In conclusion, acute hepatitis E is associated with altered metabolite and lipid profiles, significantly increased catabolism of carbohydrates, purines/pyrimidines and amino acids, and decreased levels of several glycerophospholipids.

Urinary Protein and Peptide Markers in Chronic Kidney Disease

Chronic kidney disease (CKD) is a non-specific type of kidney disease that causes a gradual decline in kidney function (from months to years). CKD is a significant risk factor for death, cardiovascular disease, and end-stage renal disease. CKDs of different origins may have the same clinical and laboratory manifestations but different progression rates, which requires early diagnosis to determine. This review focuses on protein/peptide biomarkers of the leading causes of CKD: diabetic nephropathy, IgA nephropathy, lupus nephritis, focal segmental glomerulosclerosis, and membranous nephropathy. Mass spectrometry (MS) approaches provided the most information about urinary peptide and protein contents in different nephropathies. New analytical approaches allow urinary proteomic-peptide profiles to be used as early non-invasive diagnostic tools for specific morphological forms of kidney disease and may become a safe alternative to renal biopsy. MS studies of the key pathogenetic mechanisms of renal disease progression may also contribute to developing new approaches for targeted therapy.

The development and clinical applications of proteomics: an Indian perspective

INTRODUCTION

Proteomic research has been extensively used to identify potential biomarkers or targets for various diseases. Advances in mass spectrometry along with data analytics have led proteomics to become a powerful tool for exploring the critical molecular players associated with diseases, thereby, playing a significant role in the development of proteomic applications for the clinic.

AREAS COVERED

This review presents recent advances in the development and clinical applications of proteomics in India toward understanding various diseases including cancer, metabolic diseases, and reproductive diseases. Keywords combined with 'clinical proteomics in India' 'proteomic research in India' and 'mass spectrometry' were used to search PubMed.

EXPERT OPINION

The past decade has seen a significant increase in research in clinical proteomics in India. This approach has resulted in the development of proteomics-based marker technologies for disease management in the country. The majority of these investigations are still in the discovery phase and efforts have to be made to address the intended clinical use so that the identified potential biomarkers reach the clinic. To move toward this necessity, there is a pressing need to establish some key infrastructure requirements and meaningful collaborations between the clinicians and scientists which will enable more effective solutions to address health issues specific to India.

Urine proteomics study reveals potential biomarkers for the differential diagnosis of cholangiocarcinoma and periductal fibrosis

Cholangiocarcinoma (CCA) is a primary malignant tumor of the epithelial lining of biliary track associated with endemic Opisthorchis viverrini (Ov) infection in northeastern Thailand. Ov-associated periductal fibrosis (PDF) is the precancerous lesion for CCA, and can be detected by ultrasonography (US) to facilitate early detection. However, US cannot be used to distinguish PDF from cancer. Therefore, the objective of this study was to discover and qualify potential urine biomarkers for CCA detection in at-risk population. Biomarker discovery was conducted on pooled urine samples, 42 patients per group, with PDF or normal bile duct confirmed by ultrasound. After depletion of high abundance proteins, 338 urinary proteins were identified from the 3 samples (normal-US, PDF-US, CCA). Based on fold change and literature review, 70 candidate proteins were selected for qualification by multiple reaction monitoring mass spectrometry (MRM-MS) in 90 individual urine samples, 30 per group. An orthogonal signal correction projection to latent structures discriminant analysis (O-PLS-DA) multivariate model constructed from the 70 candidate biomarkers significantly discriminated CCA from normal and PDF groups (P = 0.003). As an independent validation, the expression of 3 candidate proteins was confirmed by immunohistochemistry in CCA tissues: Lysosome associated membrane glycoprotein 1 (LAMP1), lysosome associated membrane glycoprotein 2 (LAMP2) and cadherin-related family member 2 (CDHR2). Further evaluation of these candidate biomarkers in a larger cohort is needed to support their applicability in a clinical setting for screening and monitoring early CCA and for CCA surveillance.

Hepatitis E virus genotype 3 and capsid protein in the blood and urine of immunocompromised patients

OBJECTIVES

Hepatitis E virus genotype 3 (HEV3) is responsible for acute and chronic liver disease in solid organ transplant (SOT) recipients. HEV was recently found in the urine of some acutely and chronically genotype 4-infected patients.

METHODS

We examined the urinary excretion of HEV3 by 24 consecutive SOT recipients at the acute phase of HEV hepatitis and characterized the excreted virus.

RESULTS

Urinary HEV RNA was detected in 12 (50%) of the 24 transplanted patients diagnosed with HEV hepatitis. Urinary HEV antigen (Ag) was detected in all but one of the patients (96%). The density of RNA-containing HEV particles in urine was low (1.11-1.12 g/cm³), corresponding to lipid-associated virions. The urinary HEV RNA/Ag detected was not associated with impaired kidney function or de novo proteinuria. Finally, there was more HEV Ag in the serum at the acute phase of HEV infection in SOT recipients whose infection became chronic.

CONCLUSIONS

HEV3 excreted via the urine of SOT recipients at the acute phase of HEV hepatitis has a lipid envelope. Renal function was not impaired. While urinary HEV Ag was a sensitive indicator of HEV infection, only acute phase serum HEV Ag indicated the development of a chronic infection.

Hepatitis E virus: Infection beyond the liver?

Hepatitis E virus (HEV) infections are not limited to the liver but may also affect other organs. Several diseases, including Guillain-Barré syndrome, neuralgic amyotrophy, glomerulonephritis, cryoglobulinemia, pancreatitis, lymphoma, thrombopenia, meningitis, thyroiditis and myocarditis have been observed in the context of hepatitis E. To date, the definite pathophysiological links between HEV and extrahepatic manifestations are not yet established. However, it is suggested that HEV infection might be causative based on serological studies, case series, in vitro data and animal models. In particular, neuronal and renal diseases as well as pancreatitis seem to be caused by HEV, while a causative relationship between HEV and other diseases is more doubtful. Either direct cytopathic tissue damage by extrahepatic replication, or immunological processes induced by an overwhelming host immune response, are possible origins of HEV-associated extrahepatic manifestations. Hepatologists should be aware of the possibility that acute or chronically HEV-infected patients could develop extrahepatic manifestations. Neurologists, nephrologists, rheumatologists and other groups of physicians should consider HEV infection as a potential differential diagnosis when observing one of the diseases described in this review. Ribavirin and steroids have been used in small groups of patients with extrahepatic manifestations of HEV, but the efficacy of these drugs still needs to be verified by large, multicenter studies. This article comprehensively reviews the published literature regarding HEV and extrahepatic manifestations. We discuss the probability of specific extrahepatic diseases being caused by previous or ongoing HEV infection, and summarize the published knowledge about antiviral treatment in extrahepatic disorders.

Full coding hepatitis E virus genotype 3 genome amplification method

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A new amplification method for the complete HEV coding genome was described.

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HEV genome organization and function were reviewed.

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Polymorphic amino acids of each HEV genome region were analyzed in reference sequences.

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Complete coding HEV sequence of an immunocompromised patient with acute infection was analyzed.

Hepatitis E virus (HEV) genotype 3 produces zoonotic infection associated with the consumption of infected animals. HEV infections can become chronic in immunocompromised (IC) patients. The viral genome has three well defined open reading frames (ORF1, ORF2 and ORF3) within which various domains and functions have been described. This paper (i) describes a new method of complete sequencing of the HEV coding region through overlapping PCR systems, (ii) establishes a consensus sequence and polymorphic positions (PP) for each domain, and (iii) analyzes the complete coding sequence of an IC patient. With regard to the consensus, a high percentage of PP was observed in protease (PP = 19%) and the X domain (PP = 22%) within ORF1, the N-terminal region of the S domain (PP = 22%) in ORF2, and the P1 (PP = 35%) and P2 (PP = 25%) domains in ORF3. In contrast, the ORF1 Y, ORF2 S, ORF2 M and ORF3 D1 domains were conserved in the reference sequences (0.40, 1, 0.70 and 0% of PP, respectively). The sequence from the IC patient had more mutations in the RpRp (D1235G, Q1242R, S1454T, V1480I, I1502 V, K1511R, G1373 V, E1442D, V1693 M), the terminal ORF2 S- domain (F10L, S26T, G36S, S70P, A105 V, I113 V), the X domain (T938 M, T856 V, S898A) and the helicase (S1014N, S975T, Q1133 K).

TGF-β1 gene - 509C > T promoter polymorphism modulates TGF-β1 levels in hepatitis E patients

Elevated levels of transforming growth factor-β1 (TGF-β1) and its positive correlation with Foxp3 expression in hepatitis E patients have indicated involvement of TGF-β1 in hepatitis E pathogenesis. The current study determined polymorphisms in TGF-β1 gene, plasma TGF-β1 levels and T effector (Teff) cell proliferation and explored their association in a case control study. Polymorphisms in three selected sites (- 509C > T, + 869T > C and + 915G > C) of TGF-β1 gene by PCR & restriction fragment length polymorphism methods, plasma TGF-β1 quantitation by ELISA and Teff (CD4 + CD25 -) cell proliferation by CFSE method were carried out in 277 hepatitis E patients (HE) with self-limiting infection and 233 ethnically matched healthy controls (HCs) from western India. Frequency of CT genotype of - 509C > T site was significantly higher in hepatitis E patients compared to healthy controls (p = 0.017; OR 1.53, 95% CI 1.07-2.17). Plasma TGF-β1 levels were significantly higher in HE compared to HCs. TGF-β1 level of patient group having CT genotype of - 509C > T site was significantly higher compared to those having CC or TT genotypes. Teff cell proliferation was negatively correlated with plasma TGF-β1 levels in HE patients (r = - 0.568; p = 0.014). Influence of TGF-β1 promoter (- 509C > T) polymorphism on plasma TGF-β1 levels and inverse correlation of Teff cell proliferation with plasma TGF-β1 levels in self-limiting hepatitis E patients suggest key role of TGF-β1 in augmentation of reported T regulatory cell mediated pathogenesis in hepatitis E.

[Proteomics in infectious diseases]

Infectious diseases have a high incidence in the population, causing a major impact on global health. In vitro culture of microorganisms is the first technique applied for infection diagnosis which is laborious and time consuming. In recent decades, efforts have been focused on the applicability of "Omics" sciences, highlighting the progress provided by proteomic techniques in the field of infectious diseases. This review describes the management, processing and analysis of biological samples for proteomic research.

Quantitative proteomics identifies host factors modulated during acute hepatitis E virus infection in the swine model

Hepatitis E virus (HEV) causes acute enterically transmitted hepatitis. In industrialized countries, it is a zoonotic disease, with swine being the major reservoir of human HEV contamination. The occurrence and severity of the disease are variable, with clinical symptoms ranging from asymptomatic to self-limiting acute hepatitis, chronic infection, or fulminant hepatitis. In the absence of a robust cell culture system or small-animal models, the HEV life cycle and pathological process remain unclear. To characterize HEV pathogenesis and virulence mechanisms, a quantitative proteomic analysis was carried out to identify cellular factors and pathways modulated during acute infection of swine. Three groups of pigs were inoculated with three different strains of swine HEV to evaluate the possible role of viral determinants in pathogenesis. Liver samples were analyzed by a differential proteomic approach, two-dimensional difference in gel electrophoresis, and 61 modulated proteins were identified by mass spectroscopy. The results obtained show that the three HEV strains replicate similarly in swine and that they modulate several cellular pathways, suggesting that HEV impairs several cellular processes, which can account for the various types of disease expression. Several proteins, such as heterogeneous nuclear ribonucleoprotein K, apolipoprotein E, and prohibitin, known to be involved in other viral life cycles, were upregulated in HEV-infected livers. Some differences were observed between the three strains, suggesting that HEV's genetic variability may induce variations in pathogenesis. This comparative analysis of the liver proteome modulated during infection with three different strains of HEV genotype 3 provides an important basis for further investigations on the factors involved in HEV replication and the mechanism of HEV pathogenesis.

IMPORTANCE

Hepatitis E virus (HEV) is responsible for acute hepatitis, with clinical symptoms ranging from asymptomatic to self-limiting acute hepatitis, chronic infection, or fulminant hepatitis. In industrialized countries, HEV is considered an emerging zoonotic disease, with swine being the principal reservoir for human contamination. The viral and cellular factors involved in the replication and/or pathogenesis of HEV are still not fully known. Here we report that several cellular pathways involved in cholesterol and lipid metabolism or cell survival were modulated during HEV infection in the swine model. Moreover, we observed a difference between the different swine strains, suggesting that HEV's genetic variability could play a role in pathogenesis. We also identified some proteins known to be involved in other viral cycles. Our study provides insight into the mechanisms modulated during HEV infection and constitutes a useful reference for future work on HEV pathogenesis and virulence.

[Hepatitis E: molecular virology, epidemiology and pathogenesis]

Hepatitis E represents a significant proportion of enteric transmitted liver diseases and poses a major public health problem, mainly associated with epidemics due to contamination of water supplies, especially in developing countries. Hepatitis E virus (HEV) is responsible for self-limiting acute liver oral-faecal infections. In industrialised countries, acute hepatitis E is sporadic, detected in travellers from endemic areas but also in sporadic cases with no risk factors. HEV is a non-enveloped virus with a single-stranded RNA genome classified into 4 genotypes and a single serotype. Genotypes 1 and 2 only infect humans, and are predominant in the developing countries, while 3 and 4 are predominant in industrialised countries, and also infect other species of mammals, especially pigs, and multiple evidence classifies HEV as a zoonotic agent. Some HEV chronic infections have recently been reported in kidney and liver transplant patients. The mortality rate of HEV infection is greater than hepatitis A. In addition to faecal-oral transmission, parenteral transmission of HEV has also been reported. Several vaccines are currently in development. The severity of this infection in some groups of patients, especially pregnant women, and the occurrence of chronic hepatitis, even with progression to cirrhosis, have raised interest in the application of interferon and/or ribavirin therapy.

The crystal structure of human α1-microglobulin reveals a potential haem-binding site

We describe the 2.3 Å (1 Å=0.1 nm) X-ray structure of α1m (α1-microglobulin), an abundant protein in human blood plasma, which reveals the β-barrel fold typical for lipocalins with a deep pocket lined by four loops at its open rim. Loop #1 harbours the residue Cys34 which is responsible for covalent cross-linking with plasma IgA. A single disulfide bond between Cys72 and Cys169 connects the C-terminal segment to the β-barrel, as in many other lipocalins. The exposed imidazole side chains of His122 and His123 in loop #4 give rise to a double Ni2+-binding site together with a crystallographic neighbour. The closest structural relatives of α1m are the complement protein component C8γ, the L-prostaglandin D synthase and lipocalin 15, three other structurally characterized members of the lipocalin family in humans that have only distant sequence similarity. In contrast with these, α1m is initially expressed as a bifunctional fusion protein with the protease inhibitor bikunin. Neither the electron density nor ESI–MS (electrospray ionization MS) provide evidence for a chromophore bound to the recombinant α1m, also known as ‘yellow/brown lipocalin’. However, the three side chains of Lys92, Lys118 and Lys130 that were reported to be involved in covalent chromophore binding appear to be freely accessible to ligands accommodated in the hydrophobic pocket. A structural feature similar to the well-known Cys–Pro haem-binding motif indicates the presence of a haem-binding site within the loop region of α1m, which explains previous biochemical findings and supports a physiological role in haem scavenging, as well as redox-mediated detoxification.

Cytokine profiles, CTL response and T cell frequencies in the peripheral blood of acute patients and individuals recovered from hepatitis E infection

Background

Hepatitis E is a major public health problem in the developing countries. Pathogenesis of hepatitis E virus (HEV) infection is poorly understood.

Methods

This case-control study included 124 Hepatitis E patients (46 acute and 78 recovered), 9 with prior exposure to HEV and 71 anti-HEV negative healthy controls. HEV induced CTL response by Elispot, cytokines/chemokines quantitation by Milliplex assay and peripheral CD4+ & CD8+ T cell frequencies by flow cytometry were assessed.

Results

Among the patient categories, HEV specific IFN-γ responses as recorded by Elispot were comparable. Comparisons of cytokines/chemokines revealed significantly high levels of IL-1α and sIL-2Rα during acute phase. Circulating peripheral CD4/CD8+ T-cell subsets in acute and recovered individuals were comparable compared to controls, while among patient categories CD8+T cell subset was significantly higher in recovered individuals.

Conclusions

Our findings suggest that IL-1α and sIL-2Rα play a role in the pathogenesis of acute Hepatitis E infection. Lack of robust HEV ORF2-specific CTL response in the peripheral blood of HEV infected patients during the acute and recovered phases of the disease may be associated with involvement of innate immune cells/localization of the immune events at the site of infection.

Metabonomic analysis of hepatitis E patients shows deregulated metabolic cycles and abnormalities in amino acid metabolism

Hepatitis E, which is endemic to resource-poor regions of the world, is largely an acute and self-limiting disease, but some patients have an increased susceptibility to develop fulminant hepatitis. The pathogenesis of hepatitis E in humans is poorly characterized. To understand the metabolic pathways involved in the pathophysiology of hepatitis E, we have used (1) H nuclear magnetic resonance spectroscopy to quantify various metabolites in the plasma and urine of the patients with hepatitis E. These were compared with specimens from patients with acute hepatitis B as disease controls and healthy volunteers. Data were analysed using chemometric statistical methods and metabolite databases. The main metabonomic changes found in patients with hepatitis E, but not in those with hepatitis B, included increased plasma levels of L-isoleucine, acetone, and glycerol, reduced plasma levels of glycine, and reduced urinary levels of imidazole, 3-aminoisobutanoic acid, 1-methylnicotinamide, biopterin, adenosine, 1-methylhistidine, and salicyluric acid. Patients with hepatitis E or B both showed increased levels of plasma and urinary L-proline and decreased levels of various other metabolites. Pathway analysis tools suggest the involvement of glycolysis, tricarboxylic acid cycle, urea cycle, and amino acid metabolism in patients with acute hepatitis E. These findings may help better understand the clinical and biochemical manifestations in this disease and the underlying pathophysiologic processes. Based on our findings, it would be worthwhile determining whether patients with hepatitis E are more prone to develop lactic acidosis and ketosis compared with other forms of viral hepatitis.

The hepatitis E virus ORF3 protein regulates the expression of liver-specific genes by modulating localization of hepatocyte nuclear factor 4

The hepatitis E virus (HEV) is a small RNA virus and the cause of acute viral hepatitis E. The open reading frame 3 protein (pORF3) of HEV appears to be a pleiotropic regulatory protein that helps in the establishment, propagation and progression of viral infection. However, the global cellular effects of this protein remain to be explored. In the absence of traditional in vitro viral infection systems or efficient replicon systems, we made an adenovirus based ORF3 protein expression system to study its effects on host cell gene expression. We infected Huh7 hepatoma cells with recombinant adenoviruses expressing pORF3 and performed microarray-based gene expression analyses. Several genes down regulated in pORF3-expressing cells were found to be under regulation of the liver-enriched hepatocyte nuclear factor 4 (HNF4), which regulates hepatocyte-specific gene expression. While HNF4 localizes to the nucleus, its phosphorylation results in impaired nuclear localization of HNF4. Here we report that pORF3 increases HNF4 phosphorylation through the ERK and Akt kinases, which results in impaired nuclear translocation of HNF4 and subsequently the down modulation of HNF4-responsive genes in pORF3-expressing cells. We propose that modulation of several hepatocyte specific genes by pORF3 will create an environment favorable for viral replication and pathogenesis.

Emerging and neglected tropical diseases: translational application of proteomics

The challenges of identifying and controlling emerging diseases impact individual health, as well as political, social and economic situations. In this review we discuss the role of proteomics for investigation of pathogen discovery, outbreak investigation, bio-defense, disease control, host-pathogen dynamics and vaccine development of emerging and neglected tropical diseases (NTDs). In the future the discipline of proteomics may help define multiple aspects of emerging and NTDs with respect to personalized medicine and public health.

Mass spectrometry-coupled techniques for viral-related disease biomarker identification

The advent of high-resolution mass spectrometers coupled with proteomic techniques has facilitated the discovery and characterization of novel viral proteins and the detection of virus-induced changes in the cellular proteome. These advances have enabled a more comprehensive characterization of viral interactions involved in infection and pathogenesis, and allowed the discovery of viral biomarkers. This article focuses on the role of mass spectrometry proteomic techniques to identify and characterize both prospective and verified viral biomarkers, and their implications on the diagnosis of disease.

Molecular virology of hepatitis E virus

This review details the molecular virology of the hepatitis E virus (HEV). While replicons and in vitro infection systems have recently become available, a lot of information on HEV has been generated through comparisons with better-studied positive-strand RNA viruses and through subgenomic expression of viral open reading frames. These models are now being verified with replicon and infection systems. We provide here the current knowledge on the HEV genome and its constituent proteins--ORF1, ORF2 and ORF3. Based on the available information, we also modify the existing model of the HEV life cycle.

Plasma peptidome profiling of acute hepatitis E patients by MALDI-TOF/TOF

Background

Hepatitis E is endemic to resource-poor regions, where it manifests as sporadic cases and large waterborne outbreaks. The disease severity ranges from acute self-limited hepatitis with low mortality to fulminant hepatic failure with high mortality. It is believed that the host response plays an important role in determining the progression and outcome of this disease. We profiled the plasma peptidome from hepatitis E patients to discover suitable biomarkers and understand disease pathogenesis.

Results

The peptidome (< 10 kDa) fraction of plasma was enriched and analyzed by mass spectrometry. A comparative analysis of the peptide pattern of hepatitis E patients versus healthy controls was performed using ClinPro Tools. We generated a peptide profile that could be used for selective identification of hepatitis E cases. We have identified five potential biomarker peaks with m/z values of 9288.6, 7763.6, 4961.5, 1060.572 and 2365.139 that can be used to reliably differentiate between hepatitis E patients and controls with areas under the receiver operating characteristic curve (AUROC) values of 1.00, 0.954, 0.989, 0.960 and 0.829 respectively. A number of proteins involved in innate immunity were identified to be differentially present in the plasma of patients compared to healthy controls.

Conclusions

Besides the utility of this approach for biomarker discovery, identification of changes in endogenous peptides in hepatitis E patient plasma has increased our understanding of disease pathogenesis. We have identified peptides in plasma that can reliably distinguish hepatitis E patients from healthy controls. Results from this and an earlier proteomics study are discussed.

Cancer biomarkers: are we ready for the prime time?

A biomarker is a characteristic that is objectively measured and evaluated as an indicator of normal biologic processes, pathogenic processes, or pharmacologic responses to a therapeutic intervention. In cancer, a biomarker refers to a substance or process that is indicative of the presence of cancer in the body. A biomarker might be either a molecule secreted by a tumor or it can be a specific response of the body to the presence of cancer. Genetic, epigenetic, proteomic, glycomic, and imaging biomarkers can be used for cancer diagnosis, prognosis and epidemiology. These markers can be assayed in non-invasively collected biofluids. However, few cancer biomarkers are highly sensitive and specific for cancer detection at the present time. Consequently, biomarkers are not yet ready for routine use due to challenges in their clinical validation for early disease detection, diagnosis and monitoring to improve long-term survival of patients.