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Abstract

Neuroendocrine neoplasia (NEN) is a heterogeneous group of tumours and often represents a therapeutic challenge to clinicians. The peptides chromogranin A (CgA), chromogranin B (CgB) and cocaine- and amphetamine-regulated transcript (CART) are widely distributed throughout the neuroendocrine system. CgA and CgB have been used as general NEN biomarkers for many years, while CART has only recently been identified. Of these biomarkers, CgA is the most commonly used. However, circulating CgA concentrations exhibit considerable intra-individual biological variation, are altered by proton pump inhibitors (PPIs) and somatostatin analogues and are elevated in non-NEN malignancies. Therefore, interpretation of CgA results must be in the context of these confounding factors. The effects of treatment and non-NEN conditions on circulating CgB and CART concentrations are less well understood. CgB is less affected by impaired renal function and PPIs than CgA; while, circulating CART concentrations lack a diurnal variation in humans and are more reliable markers of pancreatic NEN malignancy than CgA. The utility of circulating CgA measurements in NEN prognosis, surveillance and disease recurrence has been widely investigated. However, the utility of CgB and CART in NEN management is yet to be elucidated. Further studies are needed to establish whether CgB and CART are useful alternatives to CgA.

Keywords

Tumour markers clinical studies chromogranin A chromogranin B cocaine-regulated transcript amphetamine-regulated transcript neuroendocrine neoplasia

Introduction

Neuroendocrine neoplasia (NEN) constitutes a heterogeneous group of tumours, which are often clinically silent, thus presenting a considerable diagnostic and therapeutic challenge. Since 70% of NEN patients present with metastatic disease, these tumours are commonly associated with a poor outcome.¹ Therefore, circulating biomarkers which facilitate early diagnosis and hence improve survival are critical. Ideally, such biomarkers would also distinguish between stable and progressive tumours to guide imaging and treatment.

NEN often secrete chromogranins into the circulation which can be measured to provide information on diagnosis, treatment monitoring and disease recurrence. Chromogranins, particularly chromogranin A (CgA), are used as general NEN biomarkers, although they are not always elevated in NEN patients. Furthermore, false-positive results may occur, whereby circulating CgA is elevated in patients without a NEN. Such limitations in the diagnostic accuracy of current NEN biomarkers have led to calls for more reliable circulating biomarkers.² Cocaine- and amphetamine-regulated transcript (CART) is a recently identified NEN biomarker. We discuss its role in NEN diagnosis, with reference to chromogranins, as the most commonly used circulating NEN biomarker.

Chromogranins

Neurons and neuroendocrine cells contain membrane delimited stores of peptide hormones, biogenic amines and neurotransmitters that appear electron-dense on transmission electron microscopy. These dense-core secretory vesicles, present throughout the neuroendocrine system, store and release chromogranins. Chromogranins are a group of acidic, soluble secretory proteins. The most widely studied chromogranin is CgA, which was first isolated from chromaffin cells of the adrenal medulla.³ CgA is a single polypeptide chain of 439 amino acids and 10 dibasic cleavage sites. Chromogranin B (CgB), isolated from a rat prohormone convertase 12 (PC12) phaeochromocytoma cell line, is a larger single polypeptide chain of 657 amino acids containing 15 dibasic cleavage sites.⁴ In humans, the CgA gene is localized on chromosome 14q32 and CgB is localized to chromosome 20pter – p12.⁵ Chromogranins are pro-proteins, with multiple recognition sites for endopeptidases, including the serine endopeptidases, PC1 and PC2.⁶ Both CgA and CgB undergo post-translational processing, generating several products (Figure 1). The antibodies used in assays which measure circulating chromogranins are developed using fragments and not the whole chromogranin molecule.

Figure 1.

Representation of chromogranin A and B peptides. Below each full length representation are the processed functional peptides with their amino acid number position. Dashed lines indicate the sites of dibasic peptides where processing occurs. Both chromogranins have a disulphide bridge (S–S) located at the N-terminal end.

Functions of chromogranins

Intracellularly, chromogranins contribute to the overall biogenesis of vesicle formation and facilitate the sorting of other regulated secretory proteins. Down-regulation of CgA expression by antisense RNA in PC12 cells reduces secretory granules and reduces the number of secretory granule proteins in these cells, with CgA restoring granules and secretory granule protein levels.⁷

Processing of chromogranins gives rise to multiple bioactive peptides. The peptides formed include the vasodilator vasostatin (human CgA 1–76), the catecholamine release inhibitor catestatin (human CgA 352–372)³ and the dysglycemic peptide pancreastatin (human CgA 250–301) (Figure 1). Pancreastatin regulates glucose metabolism in cells and isolated organs by inhibiting glucose-stimulated insulin release from pancreatic islet cells, it also inhibits glucose uptake by adipocytes and hepatocytes.^8–10 CgA has been investigated considerably more than CgB, although fragments of CgB have been attributed bacteriolytic effects and in the regulation of calcium signalling.¹¹

CART

CART was first characterized as an mRNA transcript up-regulated in the rat brain following administration of psychostimulants in 1995.¹² However, 14 years previously, the first 30 amino acids of a peptide known as somatostatin (SST)-like peptide was isolated from ovine hypothalamus and partially sequenced.¹³ This partially sequenced peptide was an N-terminal portion of the peptide CART (55–102) and indicated that CART was translated into a protein product. A complete analysis of the CART cDNA revealed that it was highly conserved between rats and humans, with 95% homology at the deduced amino acid sequence.¹⁴

CART structure and processing

CART is highly conserved between species suggesting an important physiological role. In the rat, CART mRNA is alternatively spliced to produce two CART mRNA forms. One lacks 39 nucleotides in the coding region. Thus, CART is expressed as a precursor of either 116 or 129 amino acid residues. There is a predicted signal sequence of 27 amino acid residues which is cleaved to produce a mature CART protein of either 102 (long form) or 89 (short form) amino acids¹² (Figure 2). However, only the short form is found in humans.¹⁴ In humans, the CART gene is located to chromosome 5q13–14.¹⁵

Figure 2.

Representation of the CART peptide. preproCART contains a 27-amino acid signal sequence which is cleaved to produce the mature peptide. This is further processed at dibasic amino acids, indicated by the dashed lines. K and R are the single amino acid abbreviation for lysine and arginine, respectively.

CART peptides have been analysed in the rat hypothalamus, pituitary and adrenal glands. CART (42–89) and CART (49–89) are expressed in the hypothalamus. The anterior pituitary lobe contains only CART (42–89), while the posterior pituitary lobe contains only CART (49–89). CART (1–89) and CART (10–89) are both detected in the adrenal gland, and both exist in forms with or without a post-translational modification of about 80 mass units. Interestingly, there is no evidence of a translation product from the long splice variant.¹⁶

Both CART (1–102) and CART (1–89) are substrates for the PC2 and PC1/3 in vitro and in vivo.¹⁷ PC1/3 is more potent than PC2 in generating the intermediate form, CART (33–102) and CART (1–27), from long pro-CART and is exclusively responsible for generating the intermediate form CART (10–89), from the short precursor. In contrast, PC2 is much more efficient than PC1/3 in generating CART (55–102) and CART (62–102). The biological activity of CART peptides resides in CART fragments (55–102) and (62–102) with CART (55–102) being more extensively studied than any other fragment.¹⁸

CART distribution

CART mRNA and peptides are found in a number of locations in the central nervous system and the periphery. CART mRNA is expressed at particularly high levels in the hypothalamus, where it has been proposed to be the third most abundant tissue-specific mRNA.^19,20 Immunocytochemistry studies have identified CART peptides in pancreatic islet SST-producing cells in adult rats,²¹ in myenteric neurons throughout the rat gastrointestinal tract and in rat antral gastrin cells.²² CART peptides are expressed in normal rat pancreatic tissue and high amounts are expressed in rat pancreatic glucagonomas.²³ There is little data on CART distribution in the human gut, but it has been found in human intra-pancreatic neurons and in islet cells during foetal development, and to co-localize with insulin in human insulinomas.²⁴ Interestingly, a recent large study demonstrated CART-immunoreactivity in 80% NEN tumour specimens originating from thyroid, stomach, ileum, pancreas and rectum.²⁵ There is only one study which compares human tissue CgA-immunoreactivity and CART-immunoreactivity. The samples, obtained from three family members with well-differentiated neuroendocrine carcinoma, had strong CgA-immunoreactivity for all three patients with scattered CART-immunoreactivity in two patients.²⁶

Functions of CART

Evidence suggests that the CART system plays a role in feeding, stress, reward and reinforcement and endocrine regulation.

CART-immunoreactivity is localized to hypothalamic regions involved in the regulation of energy homeostasis, including the ventromedial hypothalamus, dorsomedial nucleus, lateral hypothalamus, arcuate nucleus and the paraventricular nucleus.²⁷ Early studies of CART have thus investigated its role in appetite regulation. In rats, central administration of CART (55–102) powerfully inhibits food intake. Furthermore, administration of antibodies against CART peptides increased feeding, suggesting an anorectic role for CART.²⁸ Central administration of CART (55–102) induced c-Fos expression in hypothalamic regions involved in appetite and neuroendocrine control.²⁹

The anorectic effects of CART (55–102) may be secondary, however, to effects on behaviour and motor function. Central administration of CART (55–102) causes loss of co-ordination and compromises overall motoric competence.²⁹ More recent rodent studies of the effects of CART on energy balance dispute its anorectic role have shown CART to increase food intake.^30,31

CART mRNA and peptides have been localized in the paraventricular nucleus, anterior pituitary and the adrenal glands^19,27 suggesting that CART plays a role in mediating the stress response. Corticotrophin-releasing factor (CRF) increases CART expression in cultured anterior pituitary cells, and peripheral CRF injection in rodents increases serum CART and adrenocorticotrophic hormone.³² In addition, CART increases CRF mRNA levels and CRF release from hypothalamic explants.^32,33 Interestingly, CART mRNA and CART-immunoreactivity are reduced in the arcuate nucleus of adrenalectomized rats, and this effect is reversed with corticosterone,³⁴ suggesting a role for CART in the negative feedback regulation of the hypothalamic–pituitary–adrenal (HPA) axis.

Sympathetic tone, exercise and heart failure

It has long been known that the circulating concentration of CgA varies with sympathoadrenal activity. Standing and exercise will result in a modest rise in circulating CgA concentrations which peak 2–15 min after starting activity.^35,36 Therefore, blood samples should be taken from patients at rest. Given the association of CgA with sympathetic tone it is perhaps not surprising that CgA concentrations are also elevated in patients with heart disease and CgA concentrations were associated with a higher risk of mortality.³⁷ However, the use of CgA measurement does not provide any additional prognostic information to existing heart failure biomarkers.³⁸ No studies have investigated circulating CgB or CART concentrations in exercise or human heart failure, although increased plasma concentrations of CgB have been measured in the post-myocardial infarction heart failure mouse model.³⁹

Serum versus plasma measurement

Although CgA can be measured in either serum or plasma, there are conflicting results as to whether the sample type makes a difference to the concentration measured. In six healthy volunteers, no difference in CgA concentrations was found in samples collected using various anticoagulants (heparin, EDTA or fluoride/oxalate), or none at all (serum sample).⁴⁰ Furthermore, a strong positive correlation (r = 0.9858) between serum and plasma samples was found in samples taken from 40 patients with carcinoid.⁴¹ In other studies, however, higher concentrations of CgA have been measured in plasma compared to serum in two different commercially available kits (Cis-Bio and Alpco).^42,43 A possible explanation for this difference is the formation of CgA aggregates in the presence of free calcium ions, which may be prevented by EDTA present in the plasma collection tube.⁴⁴ Given the conflicting reports, it is recommended that a laboratory using a CgA assay should establish a detailed collection protocol and reference range.

There are no published comparisons on serum and plasma measurements for CgB and CART.

In vitro stability of plasma CgA, CgB and CART

The stability of all three analytes in plasma has been assessed. Plasma CgA was unaffected by 10 cycles of freeze thawing and incubation at 37℃ for four days.⁴⁰ Plasma CgB (420–436)-like immunoreactivity (LI) decreased by 31% and CgB (440–457)-LI decreased by 4% after storage for one day at room temperature. After six days at room temperature, the decrease was 35% and 15% for plasma CgB (420–436)-LI and plasma CgB (440–457)-LI.⁴⁵ Plasma CART concentration was unchanged after an eight-hours incubation period at room temperature.⁴⁶ However, these stability studies have been performed on very few subjects; two⁴⁶ and six ⁴⁰ healthy subjects and seven NEN patients.⁴⁵ Table 1 details sample collection requirements for CgA, CgB and CART measurement.

Table 1.

Sample collection requirements for CgA, CgB and CART measurement.

CgA	CgB	CART
Drug-related effects	If possible, no proton pump inhibitors should be taken two weeks before sample collection. H2 receptor antagonists can be used as a substitute	Proton pump inhibitors may mildly elevate circulating CgB concentrations. If possible, no proton pump inhibitors should be taken two weeks before sample collection.	Not known if any treatments change plasma CART concentrations
Sample type	EDTA-plasma
Sample volume	250 µL
Sample collection procedures	After an overnight fast, collect sufficient blood into an EDTA tube and transfer to the centrifuge within 15 min of venepuncture. Spin at 1600 g for 10 min at 4℃ then transfer the plasma to a plastic tube and store at −20℃ or colder until assay. Avoid repeated freeze-thawing cycles
Reference ranges	Normal <60 pmol/L	Normal <150 pmol/L	Normal <85 pmol/L

Circulating variation

Sex and age variation

There are conflicting reports as to whether there are sex differences in CgA concentrations. Three studies have found no difference,^37,47,48 one study measuring significantly higher concentrations in men⁴⁹ and another study measuring significantly lower concentrations of CgA in men compared to women.⁵⁰ All studies used different CgA assays which may account for the conflicting results.

There is also uncertainty as to how circulating CgA concentrations change with age. One study observed no significant difference in CgA concentrations between healthy subjects under and over 50 years of age.⁵¹ Another study observed small increases in CgA concentrations with increasing age.⁴⁹ Since renal function decreases with age and circulating CgA is renally cleared, it is likely that small increases in CgA concentrations with age may reflect renal impairment.⁴⁶

There have been no published studies investigating sex and age variation on circulating CgB concentrations. There are two reports on the effects of age and sex on circulating CART concentrations in humans. In a small study of healthy controls, plasma CART concentrations were higher in men than women and this difference was more prominent in hypothyroid patients. For all controls and thyroid patients, plasma CART concentration increased with age.⁵² A subsequent larger study in healthy subjects found no significant difference in circulating CART levels in men and women.⁴⁶

Food intake

The effects of feeding on CgA are also conflicting. While one study observed no difference in concentrations of healthy subjects after an 800 kcal meal,⁵³ three other studies measured higher concentrations in post-prandial healthy subjects and NEN patients with peak concentrations circulating between 60 and 120 min post-prandially.^54–56

No studies have reported on CgB fasting and non-fasting concentrations. Fuel availability has been suggested to play a role in modulating CART levels, as 24 h food restriction prevents any daily variation in CART levels in the periphery and brain.⁵⁷ Furthermore, food restriction has been shown to decrease CART mRNA expression in the hypothalamus of mice.²⁸ However, in humans, there was no significant difference in plasma CART concentrations after consuming a 560 kcal meal in 12 healthy volunteers.⁴⁶ Plasma CART concentrations were found to be significantly higher in anorexia nervosa patients compared to healthy subjects.⁵⁸ Furthermore, for anorexic and recovered anorexic patients, there was a significant inverse correlation with plasma CART and body mass index.

Biological variation

In humans, the adrenal medulla contains the largest amount of CgA-immunoreactivity, with significantly smaller amounts found in the pituitary, pancreas, stomach and small intestine. Selective suppression of the pituitary hormones and adrenalectomy did not significantly reduce circulating concentrations of CgA, but treatment with the ganglionic blocker trimethaphan resulted in a 25% reduction of concentrations after 60 min.^53,59

The biological variation of circulating CgA concentrations has been extensively investigated. The first report examined 44 healthy controls and found an overall mean day-to-day variation of 18%.⁴⁷ Subsequent studies have since reported similar magnitudes of variation, with mean day-to-day variations ranging from 10.4%⁶⁰ to 29%⁵¹ for healthy controls, and mean variations observed in NEN patients ranging from 22%⁶¹ to 29%.⁵⁶ Once the analytical and within-subject variation had been considered, the overall critical difference required for a significant change in serial concentrations was calculated to be between 38.4% and 42.6% depending upon the concentration measured.⁶² As daily variations as high as 113% have been observed for NEN patients,⁵⁶ it may be necessary to determine a patient’s CgA variation before using the biomarker for management and monitoring to enable proper interpretation of results.

Circulating CART peptides were first measured in rats.²³ Diurnal changes in circulating CART peptide concentration have been investigated in the rat and the rhesus macaque. Daily variations in circulating CART concentrations in rats and rhesus macaques parallel the respective rhythm of circulating corticosteroids, suggesting that glucocorticoids may be involved in the regulation of circulating CART peptide.⁶³ Adrenalectomy reduces circulating CART concentrations in rats by 70% and abolished its diurnal rhythm, a reduction which can be reversed by administration of corticosterone.⁵⁷ In humans, plasma CART concentrations have been measured in five healthy volunteers throughout the day (0900 (fasting), 1200, 1500 and 1800 h) and no significant variation was observed.⁴⁶

SST analogues and acid suppressant treatment

SST analogues are an effective treatment to relieve symptoms from NEN.⁶⁴ SST reduces circulating concentrations of CgA.^51,65 The reported effects of SST analogues on CgA concentrations are variable. Infusing 0.5 mg/h of SST for 4 h reduced CgA concentrations significantly after 1 h, reaching a nadir after 2 h⁵⁹; and infusing 0.5 mg/h of octreotide for 4 h reduced CgA concentrations in healthy subjects, patients with gastric carcinoid type I and patients using proton pump inhibitors (PPIs). Reduction was significantly lower after 1 h and reached a nadir 2–3 h after commencing octreotide infusion.⁵⁴ However, another study of octreotide administration to 38 NEN patients resulted in three unresponsive patients, four demonstrating a less than 30% decrease in CgA concentration and a 30–70% decrease in the remainder.⁶⁶

PPIs increase circulating CgA concentrations. Short-term PPI treatment of 30 mg/day results in a significant rise of about 2.5-fold in either plasma or serum CgA concentrations when measured by three different commercially available CgA kits.⁴² This increase is significantly higher with increased doses of PPI.⁶⁷ Serum CgA concentration approximately doubled following medium-term PPI use (90 days),⁶⁸ and approximately trebled following long-term PPI administration (six to more than 12 months).⁶⁹ Discontinuation of PPI resulted in significant decreases of serum CgA after five days,⁶⁷ and continued to decline with a half-life of 4–5 days.⁴² H2 receptor antagonists are not associated with an increase in circulating CgA concentrations and therefore, it is recommended that they are used in place of PPIs prior to measurement of CgA.^69,70

There have been no studies investigating the affect of SST analogue treatment on circulating concentrations of CgB or CART. A single case study has reported decreasing circulating CgB concentrations in a carcinoid patient over 7 months before a subsequent rise in levels.⁷¹

Circulating concentrations of CgB may vary with PPI treatment.⁷² Plasma concentrations of CgA and CgB have been compared in 29 patients treated for more than 3 months with the PPI omeprazole. The study found that 26 of the patients had elevated CgA while only one to two patients had mildly elevated plasma CgB depending on the CgB assay used.⁷³ The study did not, however, specify the diagnosis of the patients or measure pre-treatment concentrations of CgA and CgB. To date, no studies have measured circulating CART concentrations in relation to antacid treatment.

Renal failure

The majority of filtered low molecular weight (MW) (<68 kDa) proteins are reabsorbed by the renal tubules. After reabsorption, these proteins are then further processed in the proximal tubular cells. Thus, a rise is observed in the blood concentration of many low MW proteins following a decline in renal function.^74,75 Elevations in circulating concentrations of other peptide tumour markers have been found in impaired renal function.⁷⁶

Chronic renal failure results in a rise in plasma CgA concentration.⁷⁷ In particular, renal failure resulting in serum creatinine concentrations above 884 µmol/L can result in plasma CgA concentrations similar to those found in NEN patients.⁴⁰ This makes interpretation of plasma CgA results impossible in patients with chronic kidney disease. In patients with advanced renal failure (specified as a glomerular filtration rate (GFR) <20 mL/min), CgA concentrations increased by 22-fold when compared to patients with normal renal function (GFR >100 mL/min).⁷⁸

It has been reported that CgB, unlike CgA, is not raised in patients with renal failure, although the clinically more useful CgB (439–451)-LI assay was more affected than CgB (312–331)-LI assay by impaired renal function.^73,79

A recent comparison of plasma CgA, CgB and CART concentrations in 107 subjects with GFRs ranging from normal to <15 mL/min found that CgA and CART plasma concentrations were more affected than CgB by decreasing renal function. The highest concentrations of CgA and CART were found in subjects with end stage renal failure and did not exceed 500 pmol/L for either analyte suggesting that concentrations above this may be caused by NENs.⁸⁰

Liver failure

CgA concentrations are elevated in patients with liver failure, although the elevation observed is modest compared to those caused by impaired renal function.⁴⁰ The occurrence of larger molecular forms of CgA levels in patients with liver disease suggests that the liver metabolizes CgA.⁸¹ Serum CgA concentrations measured using three different assays in 11 patients with liver cirrhosis were elevated in 46–64% of cases.⁸² Concentrations of CgA in patients with liver cirrhosis were marginally higher than CgA concentrations in chronic hepatitis but both significantly higher than concentrations in healthy subjects.⁸³

There have been no studies examining the effects of liver function on CgB and CART. A summary of conditions and treatments which can change circulating levels of CgA, CgB and CART is given in Table 2.

Table 2.

Conditions and treatments which alter circulating CgA, CgB and CART concentrations.

CgA	CgB	CART
Impaired renal function/renal failure	Mild to very elevated due to decreased renal clearance	Mild to moderate elevation due to decreased renal clearance	Mild to very elevated due to decreased renal clearance
Liver disease	Mild to moderate elevation presumed secondary to reduced hepatic CgA metabolism	Not known	Not known
Proton pump inhibitors	Elevation due to gastrin stimulated CgA release from enterochromaffin cells	Slight elevation	Not known
H2 receptor antagonists	No effect	Not known	Not known
Somatostatin analogue treatment	The effect is of somatostatin analogues on CgA release varies and may result in no effect to strong suppression Suppression is due to decreased CgA synthesis and secretion from tumours	Not known	Not known
Food intake	Mild elevation 60–120 min post-prandially due to co-release with gastrin	Not known	No effect
Exercise	Mild elevation 2–15 min after activity due to increased sympathoadrenal activity	Not known	Not known

Diagnostic use of CgA, CgB and CART

The importance of CgA in diagnosis and prognosis with NENs has been investigated for over 20 years.⁸⁴ Plasma CgA has been proposed as the most reliable NEN marker for indicating progressive disease.⁸⁵ Circulating concentrations of CgA are elevated in a variety of NENs, such as phaeochromocytoma,⁷⁷ NENs of the gastrointestinal tract, lung and ovary,^86,87 CgA is also elevated in non-functioning NENs that are not associated with secretion of a particular hormone, and hence do not present with any clinical syndrome.^88–90 Elevated circulating concentrations of pancreastatin have also been found in patients with a range of NENs, including NENs arising from the gastrointestinal tract,^91–95 neuroblastoma and ganglioneuroma.⁹⁶ Assays specific for the pancreastatin fragment only have been advocated for detecting NENs that have metastasized to the liver.⁹⁷

CgB may also be used as a general NEN biomarker. Using an antiserum directed against CgB (439–451), elevated circulating concentrations were measured in patients with gastroenteropancreatic NENs and phaeochromocytomas.⁴⁵ Elevated CgB concentrations have been detected in some NEN patients when CgA is not raised.⁷³ Plasma concentrations of CgB and its C-terminal fragment (GAWK) are elevated in patients with functioning pancreatic NEN.⁴⁵ In addition, measurement of both CgA and CgB in combination has been shown to increase detection of neuroendocrine tumours, although it was not determined if the increase was statistically significant.⁷³

Although the sensitivity and specificity of circulating CgA measurement in the biochemical diagnosis of NEN have been extensively studied, there has been less focus on CgB measurement and to date, there is one only published study on CART measurement.^{46,73,82,88,98–102} Table 3 summarizes the various studies which investigate the sensitivity and specificity of circulating CgA, CgB and CART measurement in NEN. There is considerable variation in the sensitivity of CgA measurement among the studies. These differences could arise from the heterogeneous composition of NEN subtypes used in the patient groups, the varying number of subjects used in the patient and control groups, the different cut-offs used, the different methods to obtain the cut-offs and the various different CgA assays used. Several studies have compared different commercial CgA assays on the same patient group, and unsurprisingly have found different sensitivities and specificities.^82,102,104 Recently, it has been proposed that a combination of CgA assays, differing in the CgA epitope detected, may be more useful in NEN diagnosis compared to using a single assay.¹⁰⁵

Table 3.

Comparison of the sensitivity and specificity of CgA, CgB and CART in detecting NEN.

Author	NEN (n)	Controls (n)	Assay	CgA		Assay	CgB		Assay	CART
Author	NEN (n)	Controls (n)	Manufacturer	Sensitivity	Specificity	Assay	Sensitivity	Specificity	Assay	Sensitivity	Specificity
Stridsberg et al.⁹⁸	72	40	In-house	99%	NG	In-house	88%	NG	NT
Nobels et al.⁹⁹	208	173*	In-house	58%	90%	NT		NT
Tomassetti et al.¹⁰⁰	80	28	DAKO	56%	100%	NT		NT
Seregni et al.¹⁰¹	127	103	DAKO	68%	86%	NT		NT
Stridsberg et al.¹⁰²	77	31	CIS-BIO	67%	96%	NT		NT
DAKO	85%	85%	NT		NT
Euro Diagnostica	93%	88%	NT		NT
Nehar et al.¹⁰³	158	127^†	CIS-BIO	63%	98%	NT		NT
Stridsberg et al.⁷³	86	214	DAKO	94%	72%	CgB(439-451)	57%	100%	NT
CgB(312-331)	37%	84%	NT
Zatelli et al.⁸⁸	202	129	CIS-BIO	88%	71%	NT		NT
DAKO	84%	85%	NT		NT
Bech et al.⁴⁶	131	29	In-house	86%	NG	In-house	50%	NG	In-house	56%		100%
Molina et al.⁸²	79	52	CIS-BIO	87%	100%	NT		NT
Euro Diagnostica	93%	100%	NT		NT
Epitope Diagnostics	77%	100%	NT		NT

The results are taken from various studies. NT indicates not tested, NG indicates not given.

Control samples taken from non-NEN patients.

†

Control samples taken from healthy subjects and non-NEN patients.

There has only been one study to date investigating circulating concentrations of CART in NEN patients.⁴⁶ Comparing plasma concentrations of CgA, CgB and CART in 131 patients with a range of NENs, CgA was the most sensitive of the three biomarkers, with the sensitivity of CgB and CART being comparable. However, there were differences in tumour marker sensitivity between the different subtypes of NEN with CgA detecting 94% of all midgut and unknown primary NENs, while CART measurement was elevated in 95% of all progressive pancreatic NENs. The overall sensitivity for CgB was 50%

CgA, CgB and CART in non-NEN

High circulating CgA concentrations have been identified in a range of non-NEN tumours. This finding is attributed to the occurrence of tumour neuroendocrine differentiation.^106,107 Using different CgA assays, elevated circulating CgA has been detected in patients with carcinoma of the pancreas, liver, ovary, prostate, colon and breast and colon.^{103,105,108–113} When metastatic non-NEN CgA concentrations were compared with non-metastatic non-NEN CgA concentrations, no significant difference was found.⁸² Although circulating CgA is elevated in some non-NEN tumours, it is unlikely that CgA is more sensitive than traditionally used biomarkers. For instance, CgA measurement was not as sensitive as the breast carcinoma biomarker cancer antigen (CA) 15.3¹⁰⁹ or the prostate biomarker prostate-specific antigen (PSA).¹¹⁰ Furthermore, there was no significant difference in circulating CgA concentrations between patients with prostate cancer and benign prostatic hyperplasia.¹¹¹

Data on circulating CgB and CART concentrations in patients with non-NEN are scarce. Elevated plasma CgB was found in five of 63 patients with hepatoma, four of eight patients with pancreatic adenocarcinoma⁴⁵ and three of 22 patients with prostate carcinoma.¹¹² Elevated plasma CART (>150 pmol/L) has been described in patients with pancreatic, bowel and prostate cancer.⁴⁶

Histological studies have identified CgA-immunoreactivity and CgB-immunoreactivity in prostate carcinoma. In prostate carcinoma tissue, the incidence of CgA-immunoreactivity found ranged from 10% to 100% and CgB-immunoreactivity ranged from 32% to 80%.^107,113,114 A comparison of tissue immuoreactivity and serum concentrations for CgA and CgB in 22 patients with prostate carcinoma revealed a positive correlation for CgA and no correlation for CgB.¹¹²

To date, there have been no histological studies investigating CART-immunoreactivity in non-NEN tumours.

Tumour burden, prognostic indication and monitoring

The behaviour of tumours can be unpredictable and biomarkers, if adequately monitored, can be used to establish changes in tumour progression.¹¹³ Given the possible variation that occurs in circulating biomarkers, it is necessary to first establish a baseline concentration so that treatment and recurrence may be monitored.¹¹⁵

Several studies have shown that circulating concentrations of CgA correlate with tumour burden and extent of metastases.^89,95,103 However, high circulating CgA concentrations have been measured in gastrinoma patients despite the small primary tumour size and absence of metastases, possibly due to CgA secretion from G cells.^89,116 Whilst one study observed no correlation with extra-hepatic tumour burden,¹¹⁷ another study showed high circulating CgA concentrations in patients with diffuse disease compared to local or hepatic disease.¹¹⁸ Circulating CgB concentrations have been shown to correlate with phaeochromocytoma tumour burden.⁷⁹ Currently, it is unknown whether circulating CART concentrations correlate with tumour burden.

The prognostic use of CgA has been investigated in several NEN subtypes including gasteroenteropancreatic NEN and in non-functioning pancreatic NENs.^{86,117,119,120} In all these studies, increasing plasma CgA concentrations were associated with worse survival rates.

A study comparing the prognostic value of tissue CgA-immunoreactivity and CgB-immunoreactivity in medullary thyroid carcinoma found that lower tissue CgB-immunoreactivity was associated with a significantly worse survival, while no significant difference was observed with CgA-immunoreactivity.¹²¹ However, an elevated circulating CgB concentration at the time of diagnosis was associated with a significantly worse survival rates than a normal concentration of CgB. Furthermore, the median survival was lower when compared with an elevated CgA result at diagnosis, suggesting that CgB may be a more useful prognostic indicator.¹²² One explanation for a worse survival with low tissue CgB-immunoreactivity yet elevated circulating CgB concentrations is an increased release of CgB from NEN secretory granules into the circulation, resulting in less CgB available in the cell for staining.

The prognostic value of circulating CART concentrations has not been studied. However, high CART expression in tumour samples from small bowel carcinoid patients was associated with reduced survival compared to low or no CART peptide expression.²⁶

In patients with gasteroenteropancreatic NEN, a high level of concordance has been observed between tumour burden and circulating CgA concentrations suggesting a role for CgA in detecting disease recurrence.¹⁰³ The best evidence for the role of CgA in NEN monitoring is provided by a study comparing CgA, urinary 5HIAA and radiological measurements in patients with a midgut NEN. Of all the tools used, elevated plasma CgA was the first to indicate disease recurrence.⁸⁷ No studies have investigated the CgB or CART in NEN disease recurrence. Elevated plasma CgB concentrations have been shown to return to normal in one patient with a phaeochromocytoma and four patients with a vasoactive intestinal peptide tumour (VIPoma) after tumour resection.⁴⁵ Therefore, it seems possible that disease recurrence may be accompanied by plasma CgB elevation.

Conclusion

Although CgA is widely used for diagnosis, prognosis and monitoring of NEN, it has several limitations including many non-specific causes of elevation and considerable inter-assay variation. CgB may be used as an alternative in patients taking PPIs or with chronic kidney disease. CART may be a useful NEN biomarker. However, further studies are required to evaluate its utility in NEN diagnosis and prognosis.

Footnotes

Acknowledgements

This article was prepared at the invitation of the Clinical Sciences Reviews Committee of the Association for Clinical Biochemistry.

Declaration of conflicting interests

None declared.

Funding

This research received no specific grant from any funding agency in the public, commercial or not-for-profit sectors.

Ethical approval

Ethical approval not required with regard to the content of this review.

Guarantor

SRB.

Contributorship

The authors contributed equally to the article.

References

Pape

Berndt

Muller-Nordhorn

. Prognostic factors of long-term outcome in gastroenteropancreatic neuroendocrine tumours. Endocr Relat Cancer 2008; 15: 1083–1097.

Modlin

Oberg

Chung

. Gastroenteropancreatic neuroendocrine tumours. Lancet Oncol 2008; 9: 61–72.

Banks

Helle

. The release of protein from the stimulated adrenal medulla. Biochem J 1965; 97: 40C–41C.

Lee

Huttner

. Tyrosine-O-sulfated proteins of PC12 pheochromocytoma cells and their sulfation by a tyrosylprotein sulfotransferase. J Biol Chem 1983; 258: 11326–11334.

Mahata

Kozak

Szpirer

. Dispersion of chromogranin/secretogranin secretory protein family loci in mammalian genomes. Genomics 1996; 33: 135–139.

Eskeland

Zhou

Dinh

. Chromogranin A processing and secretion: specific role of endogenous and exogenous prohormone convertases in the regulated secretory pathway. J Clin Invest 1996; 98: 148–156.

Kim

Tao-Cheng

Eiden

. Chromogranin A, an “on/off” switch controlling dense-core secretory granule biogenesis. Cell 2001; 106: 499–509.

Gonzalez-Yanes

Sanchez-Margalet

. Pancreastatin modulates insulin signaling in rat adipocytes: mechanisms of cross-talk. Diabetes 2000; 49: 1288–1294.

O'Connor

Cadman

Smiley

. Pancreastatin: multiple actions on human intermediary metabolism in vivo, variation in disease, and naturally occurring functional genetic polymorphism. J Clin Endocrinol Metab 2005; 90: 5414–5425.

10.

Sanchez-Margalet

Lucas

Goberna

. Pancreastatin: further evidence for its consideration as a regulatory peptide. J Mol Endocrinol 1996; 16: 1–8.

11.

Taupenot

Harper

O'Connor

. The chromogranin-secretogranin family. N Engl J Med 2003; 348: 1134–1149.

12.

Douglass

McKinzie

Couceyro

. PCR differential display identifies a rat brain mRNA that is transcriptionally regulated by cocaine and amphetamine. J Neurosci 1995; 15: 2471–2481.

13.

Spiess

Villarreal

Vale

. Isolation and sequence analysis of a somatostatin-like polypeptide from ovine hypothalamus. Biochemistry 1981; 20: 1982–1988.

14.

Douglass

Daoud

. Characterization of the human cDNA and genomic DNA encoding CART: a cocaine- and amphetamine-regulated transcript. Gene 1996; 169: 241–245.

15.

Dominguez

. The CART gene: structure and regulation. Peptides 2006; 27: 1913–1918.

16.

Thim

Kristensen

Nielsen

. Tissue-specific processing of cocaine- and amphetamine-regulated transcript peptides in the rat. Proc Natl Acad Sci USA 1999; 96: 2722–2727.

17.

Dey

Xhu

Carroll

. Biological processing of the cocaine and amphetamine-regulated transcript precursors by prohormone convertases, PC2 and PC1/3. J Biol Chem 2003; 278: 15007–15014.

18.

Dylag

Kotlinska

Rafalski

. The activity of CART peptide fragments. Peptides 2006; 27: 1926–1933.

19.

Couceyro

Koylu

Kuhar

. Further studies on the anatomical distribution of CART by in situ hybridization. J Chem Neuroanat 1997; 12: 229–241.

20.

Gautvik

. Overview of the most prevalent hypothalamus-specific mRNAs, as identified by directional tag PCR subtraction. Proc Natl Acad Sci USA 1996; 93: 8733–8738.

21.

Wierup

Kuhar

Nilsson

. Cocaine- and amphetamine-regulated transcript (CART) is expressed in several islet cell types during rat development. J Histochem Cytochem 2004; 52: 169–177.

22.

Ekblad

Kuhar

Wierup

. Cocaine- and amphetamine-regulated transcript: distribution and function in rat gastrointestinal tract. Neurogastroenterol Motil 2003; 15: 545–557.

23.

Jensen

Kristensen

Clausen

. The hypothalamic satiety peptide CART is expressed in anorectic and non-anorectic pancreatic islet tumors and in the normal islet of Langerhans. FEBS Lett 1999; 447: 139–143.

24.

Wierup

Sundler

. CART is a novel islet regulatory peptide. Peptides 2006; 27: 2031–2036.

25.

Landerholm

Falkmer

Jarhult

. Cocaine- and amphetamine-regulated transcript in neuroendocrine tumors. Neuroendocrinology 2011; 94: 228–236.

26.

Landerholm

Shcherbina

Falkmer

. Expression of cocaine- and amphetamine-regulated transcript is associated with worse survival in small bowel carcinoid tumors. Clin Cancer Res 2012; 18: 3668–3676.

27.

Koylu

Couceyro

Lambert

. Immunohistochemical localization of novel CART peptides in rat hypothalamus, pituitary and adrenal gland. J Neuroendocrinol 1997; 9: 823–833.

28.

Kristensen

Judge

Thim

. Hypothalamic CART is a new anorectic peptide regulated by leptin. Nature 1998; 393: 72–76.

29.

Vrang

Larsen

Kristensen

. Central administration of cocaine-amphetamine-regulated transcript activates hypothalamic neuroendocrine neurons in the rat. Endocrinology 2000; 141: 794–801.

30.

Abbott

Rossi

Wren

. Evidence of an orexigenic role for cocaine- and amphetamine-regulated transcript after administration into discrete hypothalamic nuclei. Endocrinology 2001; 142: 3457–3463.

31.

Kong

Stanley

Gardiner

. A role for arcuate cocaine and amphetamine-regulated transcript in hyperphagia, thermogenesis, and cold adaptation. FASEB J 2003; 17: 1688–1690.

32.

Stanley

Murphy

Bewick

. Regulation of rat pituitary cocaine- and amphetamine-regulated transcript (CART) by CRH and glucocorticoids. Am J Physiol Endocrinol Metab 2004; 287: E583–E590.

33.

Smith

Vaughan

Donaldson

. Cocaine- and amphetamine-regulated transcript activates the hypothalamic-pituitary-adrenal axis through a corticotropin-releasing factor receptor-dependent mechanism. Endocrinology 2004; 145: 5202–5209.

34.

Balkan

Koylu

Pogun

. Effects of adrenalectomy on CART expression in the rat arcuate nucleus. Synapse 2003; 50: 14–19.

35.

O'Connor

Bernstein

. Radioimmunoassay of chromogranin A in plasma as a measure of exocytotic sympathoadrenal activity in normal subjects and patients with pheochromocytoma. N Engl J Med 1984; 311: 764–770.

36.

Elias

Wilson

Pandian

. Chromogranin A concentrations in plasma of physically active men after acute exercise. Clin Chem 1992; 38: 2348–2349.

37.

Omland

Dickstein

Syversen

. Association between plasma chromogranin A concentration and long-term mortality after myocardial infarction. Am J Med 2003; 114: 25–30.

38.

Rosjo

Masson

Latini

. Prognostic value of chromogranin A in chronic heart failure: data from the GISSI-Heart Failure trial. Eur J Heart Fail 2010; 12: 549–556.

39.

Heidrich

Zhang

Strasser

. From bench to bedside: chromogranin B-a promising novel biomarker in heart failure. Congest Heart Fail 2011; 17: 314–315.

40.

O'Connor

Pandlan

Carlton

. Rapid radioimmunoassay of circulating chromogranin A: in vitro stability, exploration of the neuroendocrine character of neoplasia, and assessment of the effects of organ failure. Clin Chem 1989; 35: 1631–1637.

41.

Woltering

Hilton

Zolfoghary

. Validation of serum versus plasma measurements of chromogranin a levels in patients with carcinoid tumors: lack of correlation between absolute chromogranin a levels and symptom frequency. Pancreas 2006; 33: 250–254.

42.

Mosli

Dennis

Kocha

. Effect of short-term proton pump inhibitor treatment and its discontinuation on chromogranin A in healthy subjects. J Clin Endocrinol Metab 2012; 97: E1731–E1735.

43.

Glinicki

Kapuscinska

Jeske

. The differences in chromogranin A (CgA) concentrations measured in serum and in plasma by IRMA and ELISA methods. Endokrynol Pol 2010; 61: 346–350.

44.

Jeske

Glinicki

Kapuscinska

. Commentary to “chromogranin A: biological function and clinical utility in neuroendocrine tumor disease”. Ann Surg Oncol 2011; 18: 293–293.

45.

Sekiya

Ghatei

Salahuddin

. Production of GAWK (chromogranin-B 420-493)-like immunoreactivity by endocrine tumors and its possible diagnostic value. J Clin Invest 1989; 83: 1834–1842.

46.

Bech

Winstanley

Murphy

. Elevated cocaine- and amphetamine-regulated transcript immunoreactivity in the circulation of patients with neuroendocrine malignancy. J Clin Endocrinol Metab 2008; 93: 1246–1253.

47.

O'Connor

Deftos

. How sensitive and specific is measurement of plasma chromogranin A for the diagnosis of neuroendocrine neoplasia? Ann N Y Acad Sci 1987; 493: 379–386.

48.

Drivsholm

Paloheimo

Osterlind

. Chromogranin A, a significant prognostic factor in small cell lung cancer. Br J Cancer 1999; 81: 667–671.

49.

Tsao

. Development of an ELISA for the detection of serum chromogranin A (CgA) in prostate and non-neuroendocrine carcinomas. Clin Chim Acta 2001; 313: 21–29.

50.

Braga

Ferraro

Mozzi

. Biological variation of neuroendocrine tumor markers chromogranin A and neuron-specific enolase. Clin Biochem 2012; 46: 148–151.

51.

Takiyyuddin

Neumann

Cervenka

. Ultradian variations of chromogranin A in humans. Am J Physiol 1991; 261: R939–R944.

52.

Koylu E, Erdogan M, Karadeniz M, et al. Plasma CART peptide levels in thyroid patients: body mass index, gender, and age-related changes [abstract]. Washington, DC: Society for Neuroscience, 2006.

53.

Takiyyuddin

Cervenka

Pandian

. Neuroendocrine sources of chromogranin-A in normal man: clues from selective stimulation of endocrine glands. J Clin Endocrinol Metab 1990; 71: 360–369.

54.

Jianu

Fossmark

Syversen

. A meal test improves the specificity of chromogranin A as a marker of neuroendocrine neoplasia. Tumour Biol 2010; 31: 373–380.

55.

Fossmark

Jianu

Martinsen

. Serum gastrin and chromogranin A levels in patients with fundic gland polyps caused by long-term proton-pump inhibition. Scand J Gastroenterol 2008; 43: 20–24.

56.

Granberg

Stridsberg

Seensalu

. Plasma chromogranin A in patients with multiple endocrine neoplasia type 1. J Clin Endocrinol Metab 1999; 84: 2712–2717.

57.

Vicentic

. CART peptide diurnal variations in blood and brain. Peptides 2006; 27: 1942–1948.

58.

Stanley S, Connan F, Small CJ, et al. Elevated circulating levels of cocaine- and amphetamine-regulated transcript (CART) in anorexia nervosa [abstract]. In: Proceedings of the 22nd Joint Meeting ofthe British Endocrine Societies, Glasgow, UK, 24–27 March 2003, p0C30.

59.

Takiyyuddin

Baron

Cervenka

. Suppression of chromogranin-A release from neuroendocrine sources in man: pharmacological studies. J Clin Endocrinol Metab 1991; 72: 616–622.

60.

Peracchi

Conte

Gebbia

. Plasma chromogranin A in patients with sporadic gastro-entero-pancreatic neuroendocrine tumors or multiple endocrine neoplasia type 1. Eur J Endocrinol 2003; 148: 39–43.

61.

Abou-Saif

Gibril

Ojeaburu

. Prospective study of the ability of serial measurements of serum chromogranin A and gastrin to detect changes in tumor burden in patients with gastrinomas. Cancer 2003; 98: 249–261.

62.

Dittadi

Meo

Gion

. Biological variation of plasma chromogranin A. Clin Chem Lab Med 2004; 42: 109–110.

63.

Vicentic

Dominguez

Hunter

. Cocaine- and amphetamine-regulated transcript peptide levels in blood exhibit a diurnal rhythm: regulation by glucocorticoids. Endocrinology 2004; 145: 4119–4124.

64.

Modlin

Pavel

Kidd

. Review article: somatostatin analogues in the treatment of gastroenteropancreatic neuroendocrine (carcinoid) tumours. Aliment Pharmacol Ther 2010; 31: 169–188.

65.

Kos-Kudla

Zemczak

Foltyn

. Octreotide suppression test in diagnosing and predicting the outcome of therapy in patients with neuroendocrine tumors. Preliminary report. Endokrynol Pol 2007; 58: 123–129.

66.

Massironi

Conte

Sciola

. Plasma chromogranin A response to octreotide test: prognostic value for clinical outcome in endocrine digestive tumors. Am J Gastroenterol 2010; 105: 2072–2078.

67.

Pregun

Herszenyi

Juhasz

. Effect of proton-pump inhibitor therapy on serum chromogranin a level. Digestion 2011; 84: 22–28.

68.

Waldum

Arnestad

Brenna

. Marked increase in gastric acid secretory capacity after omeprazole treatment. Gut 1996; 39: 649–653.

69.

Sanduleanu

Stridsberg

. Serum chromogranin A as a screening test for gastric enterochromaffin-like cell hyperplasia during acid-suppressive therapy. Eur J Clin Invest 2001; 31: 802–811.

70.

Korse

Muller

Taal

. Discontinuation of proton pump inhibitors during assessment of chromogranin A levels in patients with neuroendocrine tumours. Br J Cancer 2011; 105: 1173–1175.

71.

Allen

Degg

Anthoney

. Monitoring the treatment of carcinoid disease using blood serotonin and plasma 5-hydroxyindoleacetic acid: three case examples. Ann Clin Biochem 2007; 44: 300–307.

72.

Stridsberg

Eriksson

Oberg

. A panel of 13 region-specific radioimmunoassays for measurements of human chromogranin B. Regul Pept 2005; 125: 193–199.

73.

Stridsberg

Eriksson

Fellstrom

. Measurements of chromogranin B can serve as a complement to chromogranin A. Regul Pept 2007; 139: 80–83.

74.

Doherty

Buchanan

Ardill

. Elevations of gastrointestinal hormones in chronic renal failure. Proc Eur Dial Transplant Assoc 1978; 15: 456–465.

75.

Hallgren

Karlsson

Lundqvist

. Serum level of immunoreactive gastrin: influence of kidney function. Gut 1978; 19: 207–213.

76.

Zeferos

Digenis

Christophoraki

. Tumor markers in patients undergoing hemodialysis or kidney transplantation. Nephron 1991; 59: 618–620.

77.

Hsiao

Mezger

O'Connor

. Chromogranin A in uremia: progressive retention of immunoreactive fragments. Kidney Int 1990; 37: 955–964.

78.

Tramonti

Ferdeghini

Annichiarico

. Relationship between renal function and blood level of chromogranin A. Ren Fail 2001; 23: 449–457.

79.

Stridsberg

Husebye

. Chromogranin A and chromogranin B are sensitive circulating markers for phaeochromocytoma. Eur J Endocrinol 1997; 136: 67–73.

80.

Bech

Ramachandran

Dhillo

. Quantifying the effects of renal impairment on plasma concentrations of the neuroendocrine neoplasia biomarkers chromogranin A, chromogranin B, and cocaine- and amphetamine-regulated transcript. Clin Chem 2012; 58: 941–943.

81.

Tsao

Liu

Chang

. Characterization of serum and urinary chromogranin A by size exclusion chromatography: impact on calibrator selection and urinary assay. J Clin Lab Anal 2001; 15: 193–198.

82.

Molina

Alvarez

niel-Quiroga

. Evaluation of chromogranin A determined by three different procedures in patients with benign diseases, neuroendocrine tumors and other malignancies. Tumour Biol 2010; 32: 13–22.

83.

Massironi

Fraquelli

Paggi

. Chromogranin A levels in chronic liver disease and hepatocellular carcinoma. Dig Liver Dis 2009; 41: 31–35.

84.

O'Connor

Deftos

. Secretion of chromogranin A by peptide-producing endocrine neoplasms. N Engl J Med 1986; 314: 1145–1151.

85.

Bajetta

Ferrari

Martinetti

. Chromogranin A, neuron specific enolase, carcinoembryonic antigen, and hydroxyindole acetic acid evaluation in patients with neuroendocrine tumors. Cancer 1999; 86: 858–865.

86.

Nikou

Marinou

Thomakos

. Chromogranin a levels in diagnosis, treatment and follow-up of 42 patients with non-functioning pancreatic endocrine tumours. Pancreatology 2008; 8: 510–519.

87.

Welin

Stridsberg

Cunningham

. Elevated plasma chromogranin A is the first indication of recurrence in radically operated midgut carcinoid tumors. Neuroendocrinology 2009; 89: 302–307.

88.

Zatelli

Torta

Leon

. Chromogranin A as a marker of neuroendocrine neoplasia: an Italian multicenter study. Endocr Relat Cancer 2007; 14: 473–482.

89.

Nobels

Kwekkeboom

Bouillon

. Chromogranin A: its clinical value as marker of neuroendocrine tumours. Eur J Clin Invest 1998; 28: 431–440.

90.

Eriksson

Oberg

Stridsberg

. Tumor markers in neuroendocrine tumors. Digestion 2000; 62: 33–38.

91.

Syversen

Mignon

Bonfils

. Chromogranin A and pancreastatin-like immunoreactivity in serum of gastrinoma patients. Acta Oncol 1993; 32: 161–165.

92.

Tateishi

Kitayama

Matsuoka

. Comparison of chromogranin A and pancreastatin levels in plasma of patients with pancreatic islet cell tumor. Life Sci 1995; 57: 889–895.

93.

Yasuda

Iguchi

Funakoshi

. Comparison of plasma pancreastatin and GAWK concentrations, presumed processing products of chromogranin A and B, in plasma of patients with pancreatic islet cell tumors. Horm Metab Res 1993; 25: 593–595.

94.

Calhoun

Toth-Fejel

Cheek

. Serum peptide profiles in patients with carcinoid tumors. Am J Surg 2003; 186: 28–31.

95.

Grath-Linden

Johnston

O'Connor

. Pancreastatin-like immunoreactivity in human carcinoid disease. Regul Pept 1991; 33: 55–70.

96.

Kogner

Bjellerup

Svensson

. Pancreastatin immunoreactivity in favourable childhood neuroblastoma and ganglioneuroma. Eur J Cancer 1995; 31A: 557–560.

97.

Ardill

O'Dorisio

. Circulating biomarkers in neuroendocrine tumors of the enteropancreatic tract: application to diagnosis, monitoring disease, and as prognostic indicators. Endocrinol Metab Clin North Am 2010; 39: 777–790.

98.

Stridsberg

Oberg

. Measurements of chromogranin A, chromogranin B (secretogranin I), chromogranin C (secretogranin II) and pancreastatin in plasma and urine from patients with carcinoid tumours and endocrine pancreatic tumours. J Endocrinol 1995; 144: 49–59.

99.

Nobels

Kwekkeboom

Coopmans

. Chromogranin A as serum marker for neuroendocrine neoplasia: comparison with neuron-specific enolase and the alpha-subunit of glycoprotein hormones. J Clin Endocrinol Metab 1997; 82: 2622–2628.

100.

Tomassetti

Migliori

Simoni

. Diagnostic value of plasma chromogranin A in neuroendocrine tumours. Eur J Gastroenterol Hepatol 2001; 13: 55–58.

101.

Seregni

Ferrari

Bajetta

. Clinical significance of blood chromogranin A measurement in neuroendocrine tumours. Ann Oncol 2001; 12(Suppl. 2): S69–S72.

102.

Stridsberg

Eriksson

Oberg

. A comparison between three commercial kits for chromogranin A measurements. J Endocrinol 2003; 177: 337–341.

103.

Nehar

Lombard-Bohas

Olivieri

. Interest of Chromogranin A for diagnosis and follow-up of endocrine tumours. Clin Endocrinol (Oxf) 2004; 60: 644–652.

104.

Ferrari

Seregni

Lucignani

. Accuracy and clinical correlates of two different methods for chromogranin A assay in neuroendocrine tumors. Int J Biol Markers 2004; 19: 295–304.

105.

Ramachandran

Bech

Murphy

. Improved diagnostic accuracy for neuroendocrine neoplasms using two chromogranin A assays. Clin Endocrinol (Oxf) 2012; 76: 831–836.

106.

Mori

Mimori

Kamakura

. Chromogranin positive cells in colorectal carcinoma and transitional mucosa. J Clin Pathol 1995; 48: 754–758.

107.

di Sant'Agnese

. Neuroendocrine differentiation in carcinoma of the prostate. Diagnostic, prognostic, and therapeutic implications. Cancer 1992; 70: 254–268.

108.

Erickson

Tsao

. Elevated serum chromogranin A is detectable in patients with carcinomas at advanced disease stages. Ann Clin Lab Sci 2000; 30: 175–178.

109.

Giovanella

Marelli

Ceriani

. Evaluation of chromogranin A expression in serum and tissues of breast cancer patients. Int J Biol Markers 2001; 16: 268–272.

110.

Albisinni

Presicce

. Serum levels of chromogranin A are not predictive of high-grade, poorly differentiated prostate cancer: results from an Italian biopsy cohort. Urol Oncol 2012; pii: S1078–S1439.

111.

Sciarra

Gentile

Monti

. Comparison of chromogranin A, insulin-like growth factor 1 and prostate-specific antigen serum markers in prostate adenocarcinoma and benign prostatic hyperplasia. Urol Int 2008; 80: 68–73.

112.

Angelsen

Syversen

Haugen

. Neuroendocrine differentiation in carcinomas of the prostate: do neuroendocrine serum markers reflect immunohistochemical findings? Prostate 1997; 30: 1–6.

113.

Pruneri

Galli

Rossi

. Chromogranin A and B and secretogranin II in prostatic adenocarcinomas: neuroendocrine expression in patients untreated and treated with androgen deprivation therapy. Prostate 1998; 34: 113–120.

114.

Abrahamsson

Falkmer

Falt

. The course of neuroendocrine differentiation in prostatic carcinomas. An immunohistochemical study testing chromogranin A as an “endocrine marker”. Pathol Res Pract 1989; 185: 373–380.

115.

Ramage

Ahmed

Ardill

. Guidelines for the management of gastroenteropancreatic neuroendocrine (including carcinoid) tumours (NETs). Gut 2012; 61: 6–32.

116.

De Herder

. Biochemistry of neuroendocrine tumours. Best Pract Res Clin Endocrinol Metab 2007; 21: 33–41.

117.

Arnold

Wilke

Rinke

. Plasma chromogranin A as marker for survival in patients with metastatic endocrine gastroenteropancreatic tumors. Clin Gastroenterol Hepatol 2008; 6: 820–827.

118.

Campana

Nori

Piscitelli

. Chromogranin A: is it a useful marker of neuroendocrine tumors? J Clin Oncol 2007; 25: 1967–1973.

119.

Janson

Holmberg

Stridsberg

. Carcinoid tumors: analysis of prognostic factors and survival in 301 patients from a referral center. Ann Oncol 1997; 8: 685–690.

120.

Ekeblad

Skogseid

Dunder

. Prognostic factors and survival in 324 patients with pancreatic endocrine tumor treated at a single institution. Clin Cancer Res 2008; 14: 7798–7803.

121.

Scopsi

Sampietro

Boracchi

. Argyrophilia and chromogranin A and B immunostaining in patients with sporadic medullary thyroid carcinoma. A critical appraisal of their prognostic utility. J Pathol 1998; 184: 414–419.

122.

Bech PR, Ramachandran R, Martin NM, et al. Chromogranin B is a prognostic marker in NETS [abstract]. Berlin, Germany: European Neuroendocrine Tumor Society, 2011.

The biochemical utility of chromogranin A,chromogranin B and cocaine- and amphetamine-regulated transcript for neuroendocrine neoplasia

Abstract

Keywords

Introduction

Chromogranins

Functions of chromogranins

CART

CART structure and processing

CART distribution

Functions of CART

Sympathetic tone, exercise and heart failure

Serum versus plasma measurement

In vitro stability of plasma CgA, CgB and CART

Circulating variation

Sex and age variation

Food intake

Biological variation

SST analogues and acid suppressant treatment

Renal failure

Liver failure

Diagnostic use of CgA, CgB and CART

CgA, CgB and CART in non-NEN

Tumour burden, prognostic indication and monitoring

Conclusion

Footnotes

Acknowledgements

Declaration of conflicting interests

Funding

Ethical approval

Guarantor

Contributorship

References