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Colorectal cancer screening: the most important facts in brief

PD Dr. med. Matthias Sauter

PD Dr. med. Matthias Sauter

March 24, 2023

reading time

12 min

It is not uncommon for the first signs of bowel cancer to go unnoticed. This makes screening examinations all the more important. In this interview, Dr Matthias Sauter explains how you can prevent the disease and which examinations you should not miss.

March is Colorectal Cancer Prevention Month. Mr Sauter, you are a specialist in gastroenterology, why is there a "Colon Cancer Awareness Month"?

Colorectal cancer is one of the most common types of cancer in Switzerland - the second most common type of cancer in women, the third most common in men and generally the most common in non-smokers. The risk of developing colorectal cancer once in a lifetime is 6 per cent for men and just under 4 per cent for women. There has also been an increase in cancer among young people, for example those under 50, in recent years.

As many people in Switzerland are not aware of the frequency, but also the preventability of this disease, the month of action in March, which as far as I know has been in existence since 2002, is very important.

In contrast to most other types of cancer, there are effective early detection tests for bowel cancer, such as the faecal test and colonoscopy, which can detect the cancer at an earlier stage and therefore allow it to be treated more effectively. Often, benign precancerous stages, known as colon polyps, can also be found and removed, which in the best-case scenario can prevent cancer.

Your answer illustrates how important preventive examinations are. In your opinion, which are the most important for the early detection of colorectal cancer? And: Is there an "optimal" screening?

In theory, an optimal screening test should be available everywhere, easy to carry out, inexpensive and without complications. In addition, screening should be reliable and accurate, which means that as few cancers as possible are missed and no misdiagnoses are made.

Although the screening tests available for colon cancer are far from perfect, they are much better than for most other types of cancer. There are several options available. One is the stool test, which looks for small amounts of blood in the stool, and the other is colonoscopy . Both methods are covered by health insurance.

Can you explain in more detail how the stool test and colonoscopy are carried out?

In the stool test, a small amount of stool is collected in a tube. There are utensils that can be used to do this easily at home. The tube is then sent to the laboratory by post, and certain types of test can also be analysed at home. If the test is positive, it is repeated every 2 years. If it is positive, a colonoscopy is carried out. It should be noted that not all people with a positive test have cancer. Blood from other causes, such as haemorrhoids, can also cause the test to be positive.

During a colonoscopy, after bowel preparation - a laxative taken at home - and the administration of a sleeping pill, the large intestine is examined via the anus using a flexible endoscope. This involves looking for tumours as well as the precursors mentioned above, the polyps.

At this point, let's take a brief look at colonoscopy - something that laypeople hear a lot about, but don't know that much about. Is the colonoscopy painful? What exactly can patients expect?

The examination is not painful, as in the vast majority of cases it is performed with a sedative. Before the examination, patients follow a diet for three days in which they avoid grains, shells and husks. The day before and on the day of the examination, they take a laxative to cleanse the colon. This does not taste very pleasant, but can also be taken with a tea or similar.

Before the examination, an infusion for the sleeping pill is placed in a vein in the arm. Pulse, blood pressure and oxygen saturation are monitored. The sleeping pill is then administered. The doctor inserts a flexible endoscope with a light source and a camera into the anus and searches the bowel thoroughly for abnormalities. It is very important firstly to take enough time and secondly that the bowel is very thoroughly cleaned so that nothing is overlooked. Patients are still a little tired after the examination, but can usually eat and drink something straight away and go home after a short monitoring session.

Due to the sleeping medication, patients are not allowed to drive on this day; they should be brought to the appointment and picked up. If a relevant other "internal" illness is known or blood thinners are being taken, it is important to inform the examiner in advance.

Stool test or colonoscopy - should one of these two screening tests be preferred? If so, which one?

Both methods have their advantages and disadvantages. Studies continue to investigate which method is "better" overall, which of course also depends on how many people actually carry out screening.

The stool test is much simpler and quicker; it requires practically no preparation. The disadvantage is the lower sensitivity (i.e. less informative value) of the individual examination compared to colonoscopy. In addition, it must be repeated every two years in order to provide a good level of certainty (this is often forgotten in reality).

The colonoscopy has the advantage that precancerous lesions can also be detected and removed and, in the best case, colon cancer can even be prevented. The colonoscopy usually has to be repeated every ten years. However, it is much more time-consuming and has a risk of complications, albeit a very low one, such as injury to the bowel.

Another alternative is "sigmoidoscopy", in which only the lowest 30 cm of the large intestine is examined. This does not require the entire laxative procedure, but instead an enema is administered before the examination. Only tumours / precursors in this area can be found, tumours further up are missed.

In my opinion, the best screening is the one that is actually carried out. This is also the opinion of many of my colleagues. Although colonoscopy detects more carcinomas and precancerous lesions, this is of no use if nobody has it done.

Many cantons in Switzerland have screening programmes in which people over a certain age are automatically asked to have one or other examination. However, this is not the case in the canton of Zurich.

It's a shame that this doesn't exist in Zurich. People often tend to assume that lifestyle plays an important role in preventing bowel cancer... Is lifestyle really important? What are the other risk factors?

Yes, lifestyle certainly plays a role. Risk factors include family predisposition, smoking, obesity and diet. As far as diet is concerned, red meat increases the risk of bowel cancer; a high-fibre diet reduces the risk. But even a vegan diet cannot completely protect against the disease.

Finally, dispel one more bowel cancer myth for us: Can digestive problems and other bowel diseases be cancer-promoting?

Chronic inflammatory bowel diseases, such as Crohn's disease and ulcerative colitis, are risk factors for colon cancer, which is why these patients are regularly screened.

Many other bowel diseases such as constipation, irritable bowel syndrome or diverticular disease are not risk factors for bowel cancer.

Portrait photo of PD Dr Matthias Sauter

PD Dr. med. Matthias Sauter

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