Current diagnostic methods allow for identification of a tumor the first time that the tumor doubles

A tumor marker is a substance found in your blood, urine, or body tissue. The term "tumor markers" may refer to proteins that are made by both healthy cells and cancer cells in the body. It may also refer to mutations, changes, or patterns in a tumor's DNA. Tumor markers are also called biomarkers.

Doctors may use tumor marker tests to learn if you have cancer. These tests can also help doctors to learn more about your cancer and help to plan treatment.

How are tumor marker tests used?

High tumor marker levels can be a sign of cancer. Along with other tests, tumor marker tests can help doctors diagnose specific types of cancer and plan treatment. Tumor marker tests are most commonly used to do the following:

Learn if a person has cancer. Higher tumor marker levels may indicate a certain type of cancer. A tumor marker test may be used as a part of your initial diagnosis.

Guide treatment decisions. Some tumor marker tests tell doctors if they should give chemotherapy or immunotherapy. Others help doctors choose which drugs may work best.

Check the progress of treatment. Changes in your tumor marker levels can show how well the treatment is working.

Predict the chance of recovery. Tumor markers can help doctors predict the cancer's behavior and response to treatment. They can also predict your chance of recovery.

Predict or watch for recurrence. Recurrence is when cancer comes back after treatment. Tumor marker tests can help predict how likely this is. That's why these tests might be part of your care after treatment ends. They may help find a recurrence sooner than other tests.

Tumor marker tests may also be used to look for cancer in people with a high risk of the disease. Or you might have these tests to learn more about the cancer when doctors first find it.

Limits of tumor marker tests

Tumor marker tests are not perfect. They are often not specific for cancer and may not be sensitive enough to pick up a cancer recurrence. The presence of tumor markers alone is not enough to diagnose cancer. You will probably need other tests to learn more about a possible cancer or recurrence. Some limits to tumor marker tests are listed below.

A condition or disease that is not cancer can raise tumor marker levels.
People without cancer can have high tumor marker levels.
Tumor marker levels can change over time. The tests may not get the same result every time.
Tumor marker levels may not go up until cancer gets worse. This does not help find cancer early, or in people at high risk. It also does not help find a recurrence.
Some cancers do not make tumor markers that are found in the blood. And, some types of cancer have no known tumor markers.
Your tumor marker levels might not go up, even if your type of cancer usually makes tumor markers.

How is a tumor marker test done?

A member of your health care team will take a sample of your blood or urine. The sample goes to a laboratory for testing. Some tests must be done more than once, because the levels of tumor markers can change regularly.

You will also need other tests to find cancer and check on treatment. This is because tumor marker results have limitations (see above) and are sometimes wrong. They might:

Show a tumor is present or growing when it is not.
Show there is no tumor when one is present, or show treatment is working when it is not.

No test is perfect. So your doctor will probably order several types of tests to find answers.

Tumor marker tests and specific cancers

Doctors use different tumor marker tests for different cancers. However, many cancers do not yet have tumor markers that can help guide care.

Ask your health care team if you will have tumor marker testing. You can also find information on tumor markers in the sections on different cancers on Cancer.Net.

Questions to ask the health care team

You might want to ask your health care team these questions.

Do you think I need any tumor marker tests? Which ones, and why?
Have you looked for tumor markers already? Which ones?
How are these tests done? How often should I have them?
Who can explain the results to me?
If I have abnormal levels of a tumor marker, what does that mean? How could this result affect my treatment plan?
Will I need tumor marker tests after my cancer treatment ends?
Where can I learn more about tumor markers and testing?

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More Information

National Cancer Institute: Tumor Markers

Certain signs and symptoms might suggest that a person could have a gastrointestinal (GI) carcinoid tumor, but tests are needed to confirm the diagnosis.

Medical history and physical exam

You will be asked questions about your general health, lifestyle habits, symptoms, and risk factors. The doctor also will probably ask about symptoms that could be caused by carcinoid syndrome, as well as those that might be caused by a mass (tumor) in the stomach, intestines, or rectum.

Some patients with carcinoid tumors also have cancers or benign tumors of other organs, so doctors may ask about symptoms that might suggest other tumors are present. A thorough physical exam will provide information about signs of carcinoid tumors and other health problems. The doctor may pay special attention to the abdomen, looking for a tumor mass or enlarged liver.

If your medical history and physical exam give the doctor reason to suspect you might have a GI carcinoid, some tests will be ordered to find out if the disease is present. These might include imaging tests, lab tests, and other procedures.

Imaging tests

Barium x-ray

These tests use a barium-containing solution that coats the lining of the esophagus, stomach, and intestines. The coating of barium helps show abnormalities of the lining of these organs. Barium studies can be used to examine the upper or lower parts of the digestive system. This type of study is often useful in diagnosing some GI carcinoid tumors, but is least effective in finding those in the small intestine.

Barium swallow: This test is used to examine the lining of the esophagus. The patient drinks a barium solution that coats the lining of the esophagus, then x-ray pictures are taken.

Upper GI series with small bowel follow-through: This test is used to examine the lining of the stomach and the first part of the small intestine.

Enteroclysis: This is another way to look at the small intestine. A thin tube is passed through the mouth or nose down through the stomach to the start of the small intestine. Barium contrast is sent through the tube, along with a substance that creates more air in the intestines, causing them to expand. X-rays of the intestines are then taken. This test may be quicker and give clearer images of the small intestine than a small bowel follow-through, but the use of a tube to give the barium makes it more uncomfortable.

Barium enema: This test is used to look at the inner surface of the colon and rectum.

Barium x-rays are used less these days than in the past. In many cases, they are being replaced by endoscopy, where the doctor looks into the esophagus, stomach, or colon with a narrow fiber optic scope.

Computed tomography (CT) scan

A CT scan is most often used to look at the chest and/or belly (abdomen) to see if GI neuroendocrine (carcinoid) tumors have spread to nearby lymph nodes or other organs such as the liver. It can also be used to guide a biopsy needle into an area of concern..

Magnetic resonance imaging (MRI) scan

MRI scans sometimes can see cancer spread to the liver better than a CT scan.

Sometimes MRI is used to look at blood vessels in the liver. This requires IV contrast and is known as MR angiography (MRA).

Radionuclide scans

Scans using small amounts of radioactivity and special cameras can be helpful in looking for GI carcinoid tumors. They can help find tumors or look for areas of cancer spread if doctors aren’t sure where it is in the body.

Positron emission tomography (PET) scan: For most types of cancer, PET scans use a form of radioactive glucose (sugar) to find tumors. This type of PET scan is useful in finding high-grade (grade 3) carcinoid tumors, but a newer type of PET scan, called a Gallium-68 PET/CT Dotatate scan is being used for low (grade 1) or intermediate-grade (grade 2) GI carcinoid tumors. It uses the radioactive agent gallium-68 dotatate which attaches to the somatostatin protein on carcinoid cells.

A special camera can detect the radioactivity. The gallium-68 PET/CT scan is slowly becoming more widely available since it was approved by the FDA in 2016 and is able to find carcinoid tumors better than an Octreoscan (described below).

Another radioactive agent, copper Cu-64 dotatate, also attaches to the somatostatin protein, and was approved in 2020 for use with a PET scan in people with a GI carcinoid tumor.

Octreoscan (somatostatin receptor scintigraphy): This test uses a drug called octreotide joined to a radioactive drug. Octreotide is a hormone-like substance that attaches to GI carcinoid cells. A small amount is injected into a vein and it travels through the blood where it attaches to GI carcinoid tumors. A few hours after the injection, a special camera can be used to show where the radioactivity has collected in the body. More scans may be done over the next few days as well. Along with showing where tumors are located, this test can help tell whether treatment with certain drugs such as octreotide and lanreotide is likely to be helpful. This test is most helpful for grade 1 and 2 GI carcinoid tumors.

I-131 MIBG scan: This is test is used much less often to find GI carcinoid tumors. It uses a chemical called MIBG that is attached to radioactive iodine (I-131). This substance is injected into a vein, and the body is scanned several hours or days later with a special camera to look for areas that picked up the radioactivity. These would most likely be GI carcinoid tumors, but other kinds of neuroendocrine tumors can also pick up this chemical.

Endoscopy

Endoscopy tests use a flexible lighted tube (endoscope) with a video camera on the end. The camera is connected to a monitor, which lets the doctor see any abnormal areas in the lining of the digestive organs clearly. If needed, small pieces of the abnormal areas can be removed (biopsied) through the endoscope. The biopsy samples can be looked at in the lab to find out if cancer is present and what kind of cancer it is.

Upper endoscopy

This test is also known as esophagogastroduodenoscopy or EGD. An endoscope is passed down through the mouth to look at the esophagus, stomach, and first part of the small bowel.

An upper endoscopy may be done in a hospital outpatient department, clinic, or doctor’s office. It usually takes 15 to 30 minutes, and most patients are given medicine in a vein to make them feel relaxed and sleepy. If you are sedated for the procedure, you will need someone to take you home.

Colonoscopy

A colonoscopy is also called lower endoscopy. It uses a special endoscope known as a colonoscope which is inserted through the anus into the colon. The doctor will be able to see the lining of the entire rectum and colon. For a clear view though, the colon must be completely cleaned out before the test. There are different ways to do this, but the most common is drinking a large amount of a laxative solution the night before and the morning of the exam.

You will be given intravenous medicine to make you feel relaxed and sleepy during the procedure. Colonoscopy can be done in a hospital outpatient department, clinic, or doctor's office. It usually takes 15 to 30 minutes, although it may take longer if a tumor is seen and/or a biopsy is taken. Because you will be sedated for the procedure, you will need someone you know to take you home afterward.

Flexible sigmoidoscopy

Flexible sigmoidoscopy is similar to a colonoscopy and can be used to look for a rectal tumor and some tumors in the lower part of the colon. This test uses a shorter, flexible, hollow tube, with a light on the end of it that is also inserted through the anus up into the colon.

Capsule endoscopy

Unfortunately, neither an upper nor lower endoscopy can reach all areas of the small intestine, where many NETs begin. A device known as a capsule endoscopy may help in some cases.

This test doesn’t really use an endoscope. Instead, the patient swallows a capsule (about the size of a large vitamin pill) that contains a light source and a tiny camera. Like any other pill, the capsule goes through the stomach and into the small intestine. As it travels (usually over about 8 hours), it takes thousands of pictures. These images are transmitted electronically to a device worn around the person’s waist, while they go on with normal daily activities. The pictures can then be downloaded onto a computer, where the doctor can watch them as a video. The capsule passes out of the body during a normal bowel movement and is discarded.

Double balloon enteroscopy

This is another way to look at the small intestine. The small intestine is very long (20 feet [6 meters]) and has too many curves to be examined well with regular endoscopy. This method gets around these problems by using a special endoscope that is made up of 2 tubes, one inside the other. First the inner tube, which is an endoscope, goes forward about a foot, and then a balloon at its end is inflated to anchor it. Then the outer tube goes forward to near the end of the inner tube and it is then anchored in place with a balloon. This process is repeated over and over, letting the doctor see the intestine a foot (30 centimeters) at a time.

This procedure is done after the patient is given drugs to make them sleepy and may be even done under general anesthesia (where the patient is asleep). The main advantage of this test over capsule endoscopy is that the doctor can take a biopsy if something abnormal is seen. As with other tests that are done under sedation, you will need someone to take you home after this procedure.

Endoscopic ultrasound (EUS)

This test uses an endoscope with a small ultrasound probe on the end. This probe releases sound waves and then uses the echoes that bounce back to create images of the digestive tract wall (or nearby lymph nodes). Putting the ultrasound probe on the end of an endoscope lets it get very close to a tumor. Because the probe is close to the area being looked at, it can make very detailed pictures.

EUS can be used to see how deeply a tumor has grown into the wall of the esophagus, stomach, intestine, or rectum. It can also help see if certain lymph nodes are enlarged and help a doctor guide a needle into a lymph node, tumor, or other suspicious area to do a biopsy. You will be sedated for this test, so you will need someone to take you home.

Biopsy

In many cases, the only way to know for sure if a person has some type of GI carcinoid tumor is to remove cells from the tumor and look at them in the lab. This procedure is called a biopsy.

There are several ways to take a sample from a GI tumor. One way is through the endoscope. When a tumor is found, the doctor can use biopsy forceps (tweezers or tongs) through the tube to take a small sample of it. Another way to sample a tumor is with a CT-guided needle biopsy.

Bleeding after a biopsy of a GI carcinoid is a rare but potentially serious problem. If serious bleeding occurs, doctors can sometimes inject drugs into the tumor to constrict blood vessels and slow or stop bleeding.

In rare cases, an endoscopic biopsy or a CT-guided needle biopsy will not be able to get enough tissue to identify the type of tumor. This is sometimes the case with tumors in the small intestine. In such cases, surgery may be needed to remove a tissue sample.

You can read more about biopsies and how they are tested in Testing Biopsy and Cytology Specimens for Cancer.

Blood and urine tests

Blood and urine tests can be very helpful in diagnosing carcinoid syndrome in patients who have symptoms that might be caused by it.

Many GI carcinoid tumors, especially those in the small intestine, make serotonin (also called 5-HT). It is probably the cause of at least some of the symptoms of carcinoid syndrome. The body breaks it down into 5-hydroxyindoleactic acid (5-HIAA), which is released into the urine. A common test to look for carcinoid syndrome measures the levels of 5-HIAA in a urine sample collected over 24 hours. These tests can help diagnose many (but not all) carcinoid tumors. Sometimes, the tumors are small and don’t release enough serotonin for a positive test result.

Some foods, including bananas, plantains, kiwi fruit, certain nuts, avocado, tomatoes, and eggplant, contain a lot of serotonin and can raise 5-HIAA levels in the urine. Medicines, including cough syrup and acetaminophen (Tylenol), can also affect the results. Ask your doctor what you should avoid before having urine or blood tests for carcinoid syndrome.

Other common tests to look for carcinoids include blood tests for chromogranin A (CgA) and gastrin. Medicines that lower stomach acid called proton-pump inhibitors (such as omeprazole/Prilosec, lansoprazole/Prevacid, esomeprazole/Nexium, and many others) can make CgA and gastrin levels high even when carcinoid tumors aren’t present. If you take any of these medicines, talk to your doctor about what you need to avoid before having these blood tests. Depending on the tumor’s location and your symptoms, your doctor might do other blood tests as well.

Some of these tests can also be used to show how well treatment is working, since the levels of these substances tend to go down as tumors shrink.