Colorectal Cancer (Bowel Cancer) Symptoms, Screening and Diagnosis

Screening and testing

There are two main paths to receiving a test for colorectal cancer. The first is instigated by the patient, who notices symptoms, visits their family doctor and is referred for tests. The second is via screening, which is instigated by the health system as a way to diagnose colorectal cancer (or pre-cancer) before it is symptomatic through the detection of polyps.


Colorectal cancer is one of the very few cancers that can be prevented through screening. It is also highly treatable if it is diagnosed in its early stages. Many countries in Europe have national screening programmes, most commonly for everyone of 50–74 years of age. If this is the case in your country, you should be automatically contacted after your 50th birthday for regular screening examinations.

What is screening looking for?

Most colorectal cancers begin as a small growth on the bowel wall – a colorectal polyp or adenoma. These small growths are usually benign (non-harmful), but some develop into cancer over time (malignant).

Finding and removing polyps may prevent colorectal cancer, and colorectal cancer is generally more treatable and curable when it is diagnosed early, before it has had a chance to spread. This is why screening for colorectal cancer is so important and everyone over the age of 50 should be screened, even if they feel completely healthy.

How is screening done?

To date, the faecal occult blood test, also called FOBT, is the only screening method recommended in the EU, followed by colonoscopy when the results of the FOBT are positive.

The FOBT is a stool-based test, which involves checking the stool for signs of cancer. A stool test is done in the comfort of your own home. Some people may find this embarrassing, but it could save your life – it is that simple. Polyps or cancer in the colon or rectum have blood vessels that may release a small amount of blood that is picked up by the stool as it passes through the colon. Stool tests check for traces of this hidden (occult) blood which cannot be seen by eye.

What’s involved?

You will be asked to collect stool samples at home. You will be given or sent a kit containing full instructions on how to do this. The test kit will have everything you need to collect the samples. Once you have collected the samples, return them as instructed in the kit.

There are two types of FOBT available in Europe:

  • Guaiac FOBT (gFOBT)
    • This test uses test cards or flushable pads coated with a plant-based substance called guaiac. This can detect traces of blood in the stool.
    • Some foods or drugs can affect the results of this test, so you may be asked to avoid certain things before testing, including red meats, items high in vitamin C, such as fruits and fruit juices, and non-steroidal anti-inflammatory drugs (NSAIDs) such as ibuprofen.
    • Frequency: Once every one or two years
  • Faecal Immunochemical Test (FIT)
    • Similar to the gFOBT, this test looks for traces of blood in the stool. However, dietary restrictions are typically not required for FIT and the test is believed to be even more accurate and sensitive than the gFOBT.
    • Frequency: Once every one or two years

What happens next?

If any of these stool tests detect blood in your sample, you will need a visual exam – usually a colonoscopy – to investigate further.

Visual exams

Visual exams include different types of tests which look at the colon and rectum for any structural abnormalities that may indicate any signs of colorectal cancer. These exams are explained below.


This is one of the most reliable tests currently available, as it allows the physician to directly view the rectum and the entire colon and detect changes or abnormalities.

What’s involved?

  • You will be advised on how to prepare for your colonoscopy, but it is likely to involve eating plain foods and taking a special bowel preparation in the form of medicines to clear your bowels in the day or two beforehand.
  • During a colonoscopy a long, flexible tube (colonoscope), with a light and small video camera on the end, is inserted into the anus and then into the rectum and colon.
  • Air may be pumped in to open up the colon to take a better look. The doctor may also take tissue samples (biopsies) or remove polyps or other areas of abnormal tissue.
  • A colonoscopy typically takes about 30 to 60 minutes. You may feel the colonoscope go in, but it should not hurt. If air is pumped in during the procedure, you may feel a sensation as though you need the toilet, but again, this should not be painful. You may be offered pain relief or sedation beforehand. After the procedure, you may feel some bloating or notice some blood in your stool. This is completely normal.
© Digestive Cancers Europe

An illustration of a colonoscopy; the colonoscope, shown as a blue tube, is inserted through the anus and rectum and into the colon and looks for abnormal areas. The inset shows a patient on a table having a colonoscopy.

Watch this video to understand how you have to prepare for a colonoscopy.

What happens next?

  • Your doctor will review the results of the colonoscopy and then share the results with you. If the doctor finds any polyps or abnormal tissue in the colon, they will be sent to a laboratory for analysis to determine whether they are cancerous, pre-cancerous or non-cancerous.
  • Frequency: It depends on your risk and the results of previous examinations. Usually, it is between every five to ten years.

Flexible sigmoidoscopy

A flexible sigmoidoscopy is similar to a colonoscopy, but whereas a colonoscopy examines the entire colon, a sigmoidoscopy covers only the lower part of the colon, known as the sigmoid colon, as well as the rectum.

What’s involved?

  • The experience is very similar to a colonoscopy (see details above) but is slightly less invasive as the tube (in this case called a sigmoidoscope), does not go as far into the colon (it is inserted into the rectum and sigmoid colon).
  • A flexible sigmoidoscopy examination typically takes about 15 minutes.

What happens next?

Your doctor will review the results of the sigmoidoscopy and then share the results with you. If a pre-cancerous polyp or cancer is found, you will need to have a colonoscopy later to look at the rest of the colon.

© Digestive Cancers Europe

An illustration of a sigmoidoscopy; a sigmoidoscope, shown as a green tube, is a thin, lighted tube that is inserted through the anus and rectum and into the sigmoid colon (the lower part of the colon). The sigmoidoscope looks for abnormal areas. The inset shows a patient on a table having a sigmoidoscopy.

CT (Computed Tomography) colonography/virtual colonoscopy

The CT colonography or virtual colonoscopy uses X-rays and computers to take two or three-dimensional images of the colon and rectum.

What’s involved?

  • Similar to a colonoscopy, before a CT colonography, you may be told to eat plain foods and take a bowel preparation before the test to ensure your bowels are empty.
  • During the procedure, a thin flexible tube is placed into your anus, and gas is used to inflate the bowel. CT scans are then taken from a number of different angles.
  • The CT scanner itself is a large metallic object that looks like a doughnut. There is an area to lie down and you will be asked to remain still while you pass through the hole of the scanner. It is painless, but you may feel slightly claustrophobic or uncomfortable. Let your doctor know if that is the case.

What happens next?

Your doctor will review the results of the CT colonography and then share the results with you. Polyps cannot be removed during this screening process, which means that a follow up colonoscopy will be needed if the test is positive.

Capsule Endoscopy

  • Capsule endoscopy uses a vitamin-size capsule containing a tiny wireless camera, which you swallow to take pictures of your digestive tract.
  • Similar to other procedures, you would need to take a bowel preparation to help empty the bowels. This test is not widely available and, as yet, it has not been proven to be as effective as a colonoscopy in detecting polyps and cancer.

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