I think most people have had a form of medical testing at some point in their life, i.e. the sampling and testing of blood, urine, saliva, stool or body tissue. In a nutshell, the medical staff are just measuring the content of a ‘substance’ and then taking a view whether this is normal or not based on pre-determined ranges. These tests are normally done as a physician’s reaction to symptom presentation or maintenance/surveillance of an existing diagnosed condition. Sometimes, abnormal results will lead to more specialist tests.
In cancer, these tests are frequently called ‘markers’. Most tumour markers are made by normal cells as well as by cancer cells; however, they are produced at much higher levels in cancerous conditions. These substances can be found in the blood, urine, stool, tumour tissue, or other tissues or bodily fluids of some patients with cancer. Most tumour markers are proteins. However, more recently, patterns of gene expression and changes to DNA have also begun to be used as tumour markers. Many different tumour markers have been characterized and are in clinical use. Some are associated with only one type of cancer, whereas others are associated with two or more cancer types. No “universal” tumour marker that can detect any type of cancer has been found.
There are some limitations to the use of tumor markers. Sometimes, noncancerous conditions can cause the levels of certain tumor markers to increase. In addition, not everyone with a particular type of cancer will have a higher level of a tumour marker associated with that cancer. Moreover, tumour markers have not been identified for every type of cancer. Tumour markers are not foolproof and other tests and checks are usually needed to learn more about a possible cancer or recurrence. Technically, a biopsy is a tumour marker but I’ll not be discussing that today. I more or less covered biopsies in my blog on NETs – Stages and Grades.
I’d also like to talk about certain other tests, in particular, hormone levels as these tests are really important to help determine the type of Neuroendocrine Tumour. The constraints mentioned above apply to hormone levels and other tests to a certain extent. The post will not cover routine blood tests (i.e. complete blood count etc) as although they may point to a problem, these tests do not directly indicate a particular cancer.
Sequencing of marker testing
The sequencing of marker testing may have been different for many patients. In my own experience, I had a biopsy and then the biochemical checks were carried out. So regardless of the results of my marker tests, I was to be diagnosed with NETs. Those with lengthy and difficult diagnostic phases will perhaps have had a different sequence with the biochemical markers providing evidence for further tests to formally diagnose. Markers alone will normally not be enough for a diagnosis but they do, however, feed into the treatment plan and provide a baseline at diagnosis and for tracking going forward.
The use of markers tends to be different on an international basis, e.g. specific marker tests can be developed in-country by independent labs. Testing can also vary between in-country labs through the use of different commercially available ‘testing kits’. Moreover, the ‘normal’ test range can vary from hospital to hospital, even within the same tests. I can only imagine that clinical staff have their own versions of risk thresholds when dealing with test results. Even when results are just above or below, individual physicians can take their own view in a subjective manner. Testing is best done at the same lab each time if possible.
Here’s two tips I always give people: 1 – always get your results (preferably on paper) and track them yourself (I use a spreadsheet). 2 – When comparing results inside patient forums, always add the unit of measurement (i.e. g/L, mmol/L, umol/L etc etc). Failure to do this can at best confuse and at worst frighten patients. Compare apples with apples not with pears!
There are many markers involved with NETs. Some do different jobs and some are just variants measuring the same thing (more or less efficiently). You may also see something called ‘gold standard’ in reference to NET Tumour markers. Although thinking is changing (more on this below) and can vary from country to country, it is generally accepted that Chromogranin A and 5HIAA are the gold standard markers for tumour bulk and tumour functionality respectively. These gold standard tests may not be applicable to every type of NET, particularly 5HIAA.
NETs are known to be heterogeneous in nature (i.e. consisting of or composed of dissimilar elements; not having a uniform quality throughout). Whilst some markers can be used widely, it follows that there are many very specialist marker tests for individual types of NET. I think this applies to 3 broad categories of NETs: Carcinoid Tumours (i.e. those secreting Serotonin and others), Pancreatic NETs (or pNETs) secreting various hormones by type; and other less common types and/or syndromes which might be considered by some to be even more complex than the former two and in some cases there are big overlaps.
Another interesting thing about NET markers is that an undiagnosed patient may undergo several specialist tests to eliminate the many possibilities that are being presented as vague and common symptoms. Sometimes this is necessary to eliminate or home in on a tumour type or syndrome/hormone involved (it’s that jigsaw thing again!).
Markers too can be divided into broad categories, those measuring how much tumour is in your body and its growth potential and those measuring how functional those tumours are. The latter can probably be expanded to measure/assess excess hormone secretion and syndromes.
Measuring Tumour bulk or load/growth prediction
Chromogranin (plasma/blood test)
Chromogranin is an acidic protein released along with catecholamines from chromaffin cells and nerve terminals. This statement alone might explain why it is a good marker to use with NETs. Depending on the test kit being used, you may see test results for Chromogranin A (CgA) and Chromogranin B (CgB) – the inclusion of CgB tends to be confined to Europe. There is also mention of Chromogranin C (CgC) in places but I’ve never heard of this being used in conjunction with NETs.
One of the disadvantages of CgA is that the results can be skewed by those taking Proton Pump Inhibitors (PPIs). Many NET patients are taking PPIs to treat GERD (….and Zollinger-Ellison Syndrome). In the long-term, this has the result of increasing gastrin levels which can lead to an increase of CgA in the blood including for some months after discontinuing. CgB is said not be as influenced by the use of PPI as CgA. In addition to the issue with PPIs, CgA levels may also be elevated in other illnesses including severe hypertension and renal insufficiency. CgB is also said to be more sensitive to Pheochromocytoma.
Elevated CgA is a constant and somewhat excitable discussion point on patient forums and not just because of the lack of unit of measurement use I discussed above. Some people get quite excited about a single test result. I refer to Dr Woltering et al (ISI Book) where it clearly states that changes in CgA levels of more than 25% over baseline are considered significant and a trend in serial CgA levels over time has been proven to be a useful predictor of tumour growth (i.e. a single test result with an insignificant rise may not be important on its own). Dr Woltering also gives good advice on marker tests when he says “normal is normal” (i.e. an increased result which is still in range is normal).
Here is a nice graphic explaining what else could be the cause of elevated CgA:
CgA appears to be a widely used tumour marker and is effective in most NETs (foregut, midgut and hindgut). It is also sensitive to Pheochromocytoma, particularly when correlated with a 131I-MIBG scan. Interestingly Chromogranin can also be used in the immunohistochemical staining of NET biopsy samples (along with other methods).
As for my own experience, my CgA was only elevated at diagnosis, remained elevated after intestinal surgery but returned to normal after liver surgery (indicating the effect of liver tumour bulk on results). It also spiked out of range when some growth in a distant left axillary node was reported in Jan 2012. Following a lymphadenectomy, it returned to normal again and has remained in range to this day. It has been a good predictor of tumour bulk for me and I’m currently tested every 6 months.
In effect, this marker does the same job as CgA. Interestingly, Pancreastatin is actually a fragment of the CgA molecule. There have been many studies (mainly in the US) indicating this is a more efficient marker than CgA, and not only because it is not influenced by the use of PPI. It has also been suggested that it’s more sensitive than CgA and therefore capable of detecting early increases in tumour burden. It has also been suggested it can be an indication of tumour ‘activity’ (whatever that means). It is widely used in the US and some physicians will use it in preference to CgA (…..although I suspect both will be tested!). According to the ISI Book (Woltering et al), Pancreastatin is only used to test mid-gut NETs.
Measuring Tumour activity/functionality/hormone/peptide levels
This is a slightly more complex area and many more tests are involved. There is probably a correlation between CgA/Pancreastatin and these type of markers i.e. a serial high level of CgA might indicate a high level of tumour bulk and therefore increased production of (say) serotonin – therefore a higher level of 5HIAA output …….. however, it frequently does not appear to work out like that, particularly when dealing with non-functioning tumours.
The type of marker for this element of NET diagnosis and surveillance will vary depending on the type of NET and its location (to a certain extent). Like tumour bulk/growth, there might be different options or test variants on an international basis. There are too many to list here, so I’ll only cover the most common.
Carcinoid Tumours (Serotonin Secreting)
I know there’s a wish to see less use of the term Carcinoid but in my opinion, there remains a need to use the term in reference to the histopathological subgroups of tumours within the NET umbrella and are associated with the same syndrome. Just to be clear, when I say ‘Carcinoid’ I do not mean ALL NETs. There are a few markers in use for measuring the functionality of this grouping of tumours. This tumour group has a tendency to secrete excess amounts of the hormone Serotonin although it differs depending on the area of the primary. For example, hindgut tumours tend to secret lower levels than foregut and midgut and therefore this test may be normal. Please also note that there are other hormones of note involved.
5HIAA. 5HIAA is a metabolite of Serotonin thus why it is a useful thing to measure to assess carcinoid tumour functionality. 5HIAA is actually the ‘gold standard’ test for functioning ‘carcinoid’ tumours. It’s a key measure of the effects of carcinoid syndrome and the risk of succumbing to carcinoid heart disease. However, there are two methods of testing: Urine and Plasma. The latter is mainly used in USA but other countries are now looking at implementing the plasma version. I know from one of my NET professional contacts that UK is currently assessing it and the comparison looks OK with some observations made on the impact of impaired renal function on the plasma results. The rather obvious key difference between the two is practicality. With the 24 hour urine, there are two key issues: 1. The logistics (i.e. lug the jug). 2. Fasting for up to 3 days prior to the test (4 if you count the day of the test). There are numerous variations on the fasting theme but most labs tend to say not to eat at least the following foods that contain high levels of serotonin: avocados, bananas, chocolate, kiwi fruit, pineapple, plums, tomatoes, and walnuts. Some lists contain additional items. With the plasma version, the fasting period is reduced to 8 hours. There are also medicinal limitations including Drugs can also alter 5-HIAA urine values, such as acetanilide, phenacetin, glyceryl guaiacolate (found in many cough syrups), methocarbamol, and reserpine. Drugs that can decrease urinary 5-HIAA levels include heparin, isoniazid, levodopa, monoamine oxidase inhibitors, methenamine, methyldopa, phenothiazines, and tricyclic antidepressants.
As for my own experience, my 5HIAA (urine) was elevated at diagnosis only returning to normal after removal of my primary and commencement of Lanreotide. It has been a good measure of tumour functionality for me and I’m currently tested every 6 months.
Other tests for the carcinoid subgroup include but not limited to:
Serum Serotonin (5-HydroxyTryptamine; 5-HT). Firstly let’s deconflict between 5HIAA above and the serotonin (5-HT) blood test. 5HIAA is a metabolite of serotonin but the serotonin test is a measure of pure serotonin in the blood. Morning specimens are preferred and this is a fasting test (10-12 hours). There is always debate on forums about Serum Serotonin results. I have Dr Liu on record as saying “a high serotonin level measured in the blood in isolation really isn’t that dangerous. It’s the 5HIAA (a breakdown product of serotonin, which is easily measured in the blood and urine) that is considered to be more indicative of persistent elevated hormone. It’s this test that is most closely related to the carcinoid heart disease”.
Histamines – Usually associated with foregut tumors. Appears to be involved in patchy rashes and flushing. The advice in the ISI NET book is no anti-histamine medication to be taken for 48 hours prior to blood draw.
Gastric NETs (Stomach)
Testing will be different depending on the Type:
- Type 1 – Typical Low Grade, tends to be caused by atrophic gastritis.
- Type 2 – Atypical Intermediate Grade and tends to be caused by gastrin secreting tumours. Type 2 normally needs a check for MEN1/Zollinger-Ellison Syndrome.
- Type 3 – Tend to be larger and more aggressive tumours.
The key makers are CgA and Gastrin although Gastrin may not be elevated in Type 3. Gastrin ph is useful to differentiate between Type 1 and Type 2. 5HIAA can be considered but Carcinoid Syndrome is rare in Gastric NETs.
Pancreatic NETs (pNETs)
pNETs can be very difficult to diagnose and not only because they share some presentational similarities to their exocrine counterparts. Some pNETs actually comprise tumours arising in the upper part of the duodenum (small intestine) close to the Pancreas. Moreover, more than half of pNETs are non-functional which increases the difficulty in suspecting and then finding the tumours. However, where there is clinical presentation or suspicion, these symptoms can lead to the appropriate testing to support the output of scans. The fasting gut profile mentioned above can be useful in identifying the offending hormones when the type of NET is not yet known.
Gut Hormones (Glucagon, Gastrin, VIP, Somatostatin, Pancreatic Polypeptide)
A gut hormone screen is used for the diagnosis of a variety of endocrine tumours of the pancreas area. Analysis includes gastrin, VIP, somatostatin, pancreatic polypeptide, and glucagon, but there may be others depending on processes used by your ordering specialist or hospital.
1. You may see this referred to as a ‘Fasting Gut Profile’ or a ‘Fasting Gut Hormone Profile’.
2. The individual hormones measured seem to differ between hospital labs.
3. The fasting conditions also vary between hospitals and labs but all agree the conditions are critical to the most accurate results. Always ask for instructions if you’re offered this test.
The gastrin test is usually requested to help detect high levels of gastrin and stomach acid. It is used to help diagnose gastrin-producing tumours called gastrinomas, Zollinger-Ellison (ZE) syndrome, and hyperplasia of G-cells, specialised cells in the stomach that produce gastrin. It may be measured to screen for the presence of multiple endocrine neoplasia type I (MEN) It may be used if a person has abdominal pain, diarrhoea, and recurrent peptic ulcers. A gastrin test may also be requested to look for recurrence of disease following surgical removal of a gastrinoma.
Vasoactive intestinal peptide (VIP) measurement is required for diagnosis of pancreatic tumour or a ganglioneuroma which secretes VIP. Administration of VIP to animals causes hyperglycaemia, inhibition of gastric acid, secretion of pancreatic bicarbonate and of small intestinal juice, and a lowering of systemic blood pressure with skin flush. These features are seen in patients with a tumour of this type which is secreting VIP.
Glucagon is measured for preoperative diagnosis of a glucagon-producing tumour of the pancreas in patients with diabetes and a characteristic skin rash (necrolytic migratory erythema).
Pancreatic polypeptide (PP) production is most commonly associated with tumours producing vasoactive intestinal polypeptide and with carcinoid syndrome and, less commonly, with insulinomas and gastrinomas.
When secreted by endocrine tumours, somatostatin appears to produce symptoms similar to those seen on pharmacological administration, i.e. steatorrhoea, diabetes mellitus and gall stones.
There are several types of pNETs, each with their own syndrome or hormone issue. When they are suspected due to the presentational symptoms, the markers that could be used are listed below. These types of tumours are complex and can be related to one or more syndromes. A patient may be tested using multiple markers to include or exclude these. Depending on other factors, some physicians may recommend additional marker testing in addition to the most common types below.
Insulinoma – Insulin, Proinsulin, C-peptide
Gastrinoma– Gastrin, Gastrin pH
Glucagonoma – Glucagon, Insulin, Pancreatic Polypeptide (PP), Adrenocorticotropic hormone (ACTH)
VIPoma – Vasoactive Intestinal Polypeptide (VIP), Electrolytes (due to profuse diarrhea)
Somatostatinoma – Somatostatin (plasma somatostatin like immunoreactivity)
PPoma – Pancreatic Polypeptide (PP)
Pheochromocytoma/Paraganglioma – Adrenaline-producing tumours. Plasma and urine catecholamines, plasma free total metanephrines, urine total metanephrines, vanillylmandelic acid (VMA)
Medullary Thyroid Cancer – Calcitonin
Parathyroid– Parathyroid hormone (PTH), Serum Calcium
Pituitary/Cushings – Adrenocorticotropic hormone (ACTH), Cortisol
Multiple Endocrine Neoplasia (MEN). Complex and tends to be multiple instances of some of the tumours above. For a breakdown of MEN types and locations, check out my MEN blog ‘Running in the Family’
Carcinoid Heart Disease(CHD). I’m not really talking directly about a tumour here but thought it would be useful to include a blood test called NT-proBNP. I’ve left a link to my CHD blog in the paragraph heading for those who wish to learn more about CHD in general. For those not offered an annual Echocardiogram or are ‘non-syndromic’ there is a screening test that can give an indication of any heart issue which might then need further checks.
The Future – Molecular Markers?
This is testing using DNA and genes. Exiting but complex – check out this article which involved some NETs.
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