Tests after a diagnosis of colon or rectal cancer

If the initial tests| show that there is a cancer in the colon or rectum, further tests will be done to find out the size and position of the cancer, and to see whether it has spread. This process is called staging| , and may take some time. The results will help you and your doctor decide on the best treatment for you. Sometimes these tests may be done again, during and after treatment, to check on your progress.

The following additional tests are used most often: 

• Chest x-rays – to check the health of your heart and lungs
• Blood tests
• Abdominal ultrasound scan – uses sound waves to look at internal organs
• CT (computerised tomography) scan – uses x-rays to build up a three-dimensional picture of the inside of your body
• PET (positron emission tomography) scan – a scan that shows how tissues inside your body are working
• Combined PET and CT scan
• MRI (magnetic resonance imaging) scan – uses magnetic fields to build up a series of cross-sectional pictures of your body 

 

What the tests involve Back to top

Blood tests

You will probably have blood tests to assess your general health, and also to check for a particular protein that is sometimes produced by bowel cancer cells. The protein is called carcinoembryonic antigen (CEA). Proteins produced by cancer cells are sometimes called tumour markers as they may give an indication about how treatment is working or whether a cancer is coming back. 

Abdominal ultrasound scan

This uses sound waves to look at internal organs, such as the liver and the inside of the abdomen, to see whether the cancer has spread to other organs. You will usually be asked not to eat or drink for at least six hours before the test.

Once you are lying comfortably on your back, a gel is spread onto your abdomen. A small device that produces sound waves is passed over the area. The sound waves are then converted into a picture by a computer. The test only takes a few minutes.

In some situations you may have a probe (like a tube) inserted into the rectum to produce ultrasound scans. This is known as an endoscopic ultrasound (EUS). 

CT (computerised tomography) scan

A CT scan can show the size of the cancer and whether it has spread beyond the bowel. The scan is painless but takes longer than an ordinary x-ray (10–30 minutes).

CT scans use a small amount of radiation, which is unlikely to harm you and will not harm anyone you come into contact with. You will be asked not to eat or drink for at least four hours before the scan.

You may be given a drink or injection of a dye, which allows particular areas to be seen more clearly. This may make you feel hot all over for a few minutes. If you are allergic to iodine, or have asthma, you could have a more serious reaction to the injection, so it’s important to let your doctor know beforehand.

Just before the scan, a similar liquid is also passed into your back passage through a small tube. Although this may be unpleasant at the time, it makes sure that the best possible picture is produced. Once you are in position, the scan will be taken.

You will probably be able to go home when the scan is over.

PET (positron emission tomography) scan

PET scans are a newer type of scan and you may have to travel to a specialist centre to have one. They are not always necessary but you can discuss with your doctor whether one would be useful in your case. PET scans can be used to accurately define the cancer and find out if it has spread to other parts of the body.

A PET scan uses low-dose radioactive glucose (a type of sugar) to measure the activity of cells in different parts of the body. A very small amount of the glucose is injected into a vein, usually in your arm. A scan is then taken a couple of hours later. Areas of cancer are usually more active than surrounding tissue and show up on the scan.

PET/CT scan

Usually a PET scan is combined with a CT scan. A small amount of a radioactive substance is injected in the same way as a standard PET scan, and then the CT scan takes a series of x-rays. The scanner combines the two different types of information and allows your doctor to measure any changes in the activity of cells and to know exactly where in the body the changes are.

A PET/CT scan can be used to show whether the cancer has spread and to give information that will help the doctors decide on the best treatment. It is not used to replace a CT scan, so you may need to have both types of scans.

MRI (magnetic resonance imaging) scan

If you have a rectal cancer, this test can help to show the stage of the cancer and can give the surgeon information to help them plan an operation or to decide whether radiotherapy should be given before surgery. People with a rectal cancer will often have an MRI scan before surgery.

MRI scans aren’t always needed for people with a colon cancer and your doctor can discuss whether you need to have this type of scan.

Before the scan you may be asked to complete and sign a checklist. This is to make sure that it’s safe for you to have an MRI scan, because the scanner is a powerful magnet. The checklist asks about any metal implants you may have, for example a pacemaker, surgical clips, bone pins etc. You should also tell your doctor if you have ever worked with metal or in the metal industry as very tiny fragments of metal can sometimes lodge in the body. If you do have any metal in your body it’s likely that you won’t be able to have an MRI scan. In this situation another type of scan can be used.

Before having the scan, you’ll be asked to remove any metal belongings including jewellery. Some people are given an injection of dye into a vein in the arm, which doesn’t usually cause discomfort. This is called a contrast medium and helps the images from the scan show up more clearly. During the test you’ll be asked to lie very still on a couch inside a long cylinder (tube) for about 30 minutes. It’s painless but can be slightly uncomfortable, and some people feel a bit claustrophobic during the scan. It’s also noisy, but you’ll be given earplugs or headphones. You’ll be able to hear, and speak to, the person operating the scanner.