Article: Bowel cancer - Screening and prevention
We are often confronted with the topic of screening in our everyday lives, for example on subway posters, in a doctor’s practice, or when talking to friends and relatives. Bowel cancer is one of the types of cancer screening programs often focus on. The message usually reads “prevention is better than cure”, which sounds reasonable. Bowel cancer screening can indeed lower the risk of getting bowel cancer and dying. But this is only one side of the coin: the screening examinations can have complications, too. And the benefit of screening is smaller than many people think it is. In short: bowel cancer screening has advantages and disadvantages.
This information aims to help you form your own opinion on the advantages and disadvantages of different methods of bowel cancer screening so that you can make your own decision. If you want more concise information, you can read the most important information here (URL: http://www.informedhealthonline.org/here.799.en.html) .
Table of contents
- Bowel cancer and screening
- How does bowel cancer develop?
- Does bowel cancer have any signs or symptoms?
- What are the aims of screening?
- Who is screening for?
- How common is bowel cancer?
- Who has a higher risk?
- Screening methods
- Stool tests for hidden blood
- The test
- Advantages and disadvantages of chemical stool tests
- Other stool tests
- The examination
- Advantages and disadvantages
- The examination
- Advantages and disadvantages
- What statutory health insurance pays for in Germany
- Stool tests for hidden blood
- Personal aspects
- Feeling embarrassed
- Bowel cancer in the family
- Making a decision
1. Bowel cancer and screening
1. Bowel cancer and screening
1.1. How does bowel cancer develop?
The entire bowel (intestine) is made up of the small bowel, which is 3 to 5 meters (about 3.3 to 5.5 yards) long, and the large bowel, which is about 1.5 meters (about 1.6 yards) long. The colon and rectum are parts of the large bowel. The rectum is the last part of the bowel, which ends at the anus with the anal canal. Bowel cancer almost always develops in the colon or rectum, which is why it is also called colorectal cancer. Although the small bowel is a lot longer than the large bowel, cancer there is a lot rarer. You can read more about how the bowel works here (URL: http://www.informedhealthonline.org/here.593.en.html) .
Bowel cancer almost always develops from certain bowel polyps (adenomas). These are non-cancerous (benign) growths in the mucous membrane of the bowel. Bowel polyps are common: about 20 to 30% of all people over 50 have at least one polyp in their bowel. Most bowel polyps stay small and are not dangerous. Only a few of them change and can then become cancerous (malignant). This happens very slowly: on average, it takes ten years for cancer to develop from a changed bowel polyp.
1.2. Does bowel cancer have any signs or symptoms?
Bowel cancer often does not cause any symptoms for a long time and can therefore remain unnoticed at first. Sometimes it leads to certain symptoms, such as abdominal pain or changes in bowel habits. How often or what time someone goes to the toilet may change, for example, or there may be a tendency to be constipated or to experience increased diarrhea at times. Other possible signs are blood or mucus in the stool. However, these symptoms can be caused by many other things as well. They are usually either caused by a harmless condition, or the symptoms are signs of another benign illness like hemorrhoids or an inflammation of the bowel. If you see blood in your stool or are worried about other symptoms you have, it makes sense anyway to see a doctor about it. You can find more information about possible signs of bowel cancer here (URL: http://www.informedhealthonline.org/here.142.en.html) .
1.3. What are the aims of screening?
Screening tests for bowel cancer have two aims: Firstly, they are done to detect bowel cancer before it causes any symptoms and to improve the chances of being cured. Secondly, screening offers the chance to prevent bowel cancer if the doctor detects and removes polyps that might have developed into bowel cancer later.
1.4. Who is screening for?
In Germany, statutory health insurance funds offer bowel cancer screening to members over the age of 50 years. People with a certain hereditary predisposition for bowel cancer can use specific care and have earlier and more frequent tests for bowel cancer. These predispositions include conditions called hereditary non-polyposis colorectal cancer (HNPCC) and familial adenomatous polyposis (FAP). Polyposis means “many polyps”. People with FAP sometimes have more than 100 of these growths in their bowel.
1.5. How common is bowel cancer?
In Germany, a bowel tumor is detected in 1 out of 13 men and in 1 out of 15 women during the course of their lives. The risk increases with age: Many people who have bowel cancer are already over 75 years of age. Bowel cancer is rare in people under 50 years of age.
Sometimes bowel cancer is incorrectly regarded as a disease that typically affects only men. Even though it does affect men more often, women can also get bowel cancer. On average, the disease occurs in men at an earlier age than it does in women, however.
The following tables give an approximate idea of how high the probability is of getting bowel cancer at a certain age in the next 10 years. These are average values – a person’s individual risk also depends on personal risk factors, which we will describe in the next section.
Risk of bowel cancer in men:
Number of men who will get bowel cancer in the next 10 years
2 out of 1,000
9 out of 1,000
23 out of 1,000
37 out of 1,000
Risk of bowel cancer in women:
Number of women who will get bowel cancer in the next 10 years
2 out of 1,000
6 out of 1,000
15 out of 1,000
24 out of 1,000
1.6. Who has a higher risk?
Various factors influence how high the risk is for someone to get bowel cancer. Chronic inflammatory diseases of the bowel like Crohn’s disease or ulcerative colitis can increase the risk of bowel cancer. Depending on how extensive such a chronic inflammatory disease of the bowel is and how long it lasts, having examinations more frequently can be an option. If first-degree relatives have had bowel cancer, the risk is higher too. First-degree relatives are parents, siblings and children.
2. Screening methods
An ideal screening test would be able to detect cancer in the bowel reliably and early so that the tumor would still be small and easy to remove. The test would not sound alarm for people who do not have bowel cancer. In addition, this test would be easy, short, and pain-free for men and women. Unfortunately, none of the examinations used for bowel cancer screening on offer fulfill all of these requirements. Statutory health insurance funds in Germany cover two methods: a test for hidden (occult) blood in the stool (stool test) and an endoscopic examination of the large bowel called colonoscopy (or coloscopy).
Sigmoidoscopy is another endoscopic examination, where only the lower part of the bowel is examined. It is one of the best-tested methods, but it is not used routinely for screening in Germany. Statutory health insurance funds to not cover the costs of this examination as part of a screening.
Virtual colonoscopy using magnetic resonance tomography (MRT) and capsule endoscopy are two other types of examination currently being tested for use in bowel cancer screening. However, these methods have not been tested yet in conclusive studies on screening so that it is not clear how suitable they are for bowel cancer screening. In Germany, statutory health insurance funds do not pay for these examinations as part of a screening. But some doctors offer them as an IGeL procedure. IGeL stands for the German individuelle Gesundheitsleistungen (individual health care services), meaning medical procedures that have to be paid for out-of-pocket.
Other options for detecting bowel cancer are digital-rectal examination, where the doctor feels the inside of the rectum with a finger, double-contrast examination of the large bowel (a special x-ray method) and computed tomography (CT) of the large bowel. These examinations are usually not used in bowel cancer screening because their benefits are not well-tested. Digital-rectal examination, for example, is not very precise. In an x-ray or a CT of the large bowel the body is exposed to radiation. So these examinations are only to be used if there is concrete suspicion of bowel cancer and/or if someone has symptoms, but not for screening. We will explain chemical stool tests, colonoscopy and sigmoidoscopy in more detail here.
2.1. Stool tests for hidden blood
Bowel cancer and advanced bowel polyps can cause bleeding in the bowel. Stool tests – also called stool blood test, or fecal occult blood tests (FOBT) – can detect these traces of blood. They do not give reliable information, however, because only few tumors and polyps leave traces of blood in the stool. Blood in the stool can also be caused by harmless conditions. This is why stool blood tests are rather meant to be done as a preliminary test. If the results indicate blood in the stool, in Germany the doctor will offer you a colonoscopy to find the cause. German statutory health insurance funds pay both for the stool test and the following colonoscopy.
Stool tests only provide an opportunity to find polyps or bowel cancer early if a suspicious finding in the stool test is followed up by an endoscopy of the bowel. So it only makes sense to do a stool test if you are also prepared to have an endoscopy of the bowel if necessary.
Chemical stool tests are the most commonly used stool tests. Using a chemical reaction, these tests detect parts of hemoglobin, a protein in the red blood cells. These are the only stool tests paid for by statutory health insurance funds in Germany. This is why we will explain these chemical stool tests in more detail here. Three chemical stool tests are used for the screening tests paid for by the statutory health insurance funds in Germany: Hämoccult, HemoFec and HemoCare.
2.1.1. The test
Stool tests can find traces of blood you cannot see with the naked eye. To do the test, two pea-sized samples of stool are put on a special test card with an applicator. These test cards can be closed with a flap like an envelope. A test set contains three test cards for samples of three successive bowel movements. You can prepare the stool test at home and take it to your doctor’s practice either in person or by mail. A laboratory will then check the stool samples for blood.
Certain foods and medications can distort stool test results. These mainly include red meat like beef, lamb and liver, for example. This is why it is recommended to avoid these foods before doing the test. Anti-clotting medications like acetylsalicylic acid (ASA, or ASS in German) and larger amounts of vitamin C can also influence stool test results. If you are not sure whether you are taking medications that might distort the test result and whether you can stop taking them for some time, it is good to talk with your doctor about it well before taking the test. You will find more information on how to prepare the stool test correctly in the test instructions.
2.1.2. Advantages and disadvantages of chemical stool tests
This stool test has the advantage of being rather easy to do and having no direct adverse effects. It is also important that the chemical stool test was evaluated in large trials showing that men and women can lower their risk of dying from bowel cancer with this test– provided they also have an endoscopy of the bowel after a positive test result.
The disadvantage of the test is that it is not very reliable. The test often has a suspicious result despite there being no cancer – this is called a false-positive test result. It may happen because hemorrhoids, stomach ulcers or inflammations can also bleed into the stomach and bowel, for example. A false-positive result can cause unnecessary worrying before an endoscopy of the bowel gives the all-clear signal.
About 5 to 8 out of 10 suspicious test results prove afterwards to be a false alarm because the doctor does not find a polyp or cancer in the endoscopy of the bowel following the stool test. Below we will describe how an endoscopy of the bowel is done and what its risks are.
The second possible error is that the results of the stool test are normal although someone does have polyps or bowel cancer. This is called a false-negative test result. About 4 to 7 out of 10 cancerous bowel tumors are not detected in a stool test (about 40 to 70%). So it is important to take any symptoms that worry you seriously – even though the last test might have been normal.
Research results on chemical stool tests
Trials show that, if a chemical stool test is done every two years, fewer people over 45 years of age die of bowel cancer. Expressed in numbers, trials over a period of more than 10 years had the following results:
- Out of 1,000 people who did not do the test, about 10 died of bowel cancer.
- Out of 1,000 people who did the test regularly, about 8 to 9 died of bowel cancer.
This means that the screening saved 1 to 2 out of 1,000 people from dying of bowel cancer.
2.1.3. Other stool tests
Other tests are offered as an alternative to chemical stool tests. These include immunological stool tests, a test called the M2-PK stool test and DNA stool tests. Immunological tests also detect hidden blood in the stool. The M2-PK stool test looks for an enzyme in the stool supposed to indicate bowel cancer. The DNA stool test looks for traces of cancer cells in the stool.
These stool tests can also only give indications of bowel cancer. They can only prevent cancer if suspicious results are followed by an endoscopy of the bowel. So far only chemical stool tests have been shown to be able to reduce the number of people dying from bowel cancer in conclusive trials. It cannot be said with certainty yet whether the other tests are more suitable for screening. In Germany, statutory health insurance funds do not pay for these tests.
In a sigmoidoscopy the doctor examines about the last 60 centimeters (about 24 inches) of the large bowel with a particular kind of endoscope called sigmoidoscope. This is a flexible tube that has a small light and a camera attached to it. An endoscope enables the doctor to look at the wall of the bowel. Polyps or unusual looking parts of the mucous membrane found in an endoscopy can be removed during the procedure through the endoscope with a small wire loop or forceps. If tissue is suspected to be cancerous, the doctor can take tissue samples and have them examined more closely in a laboratory.
A sigmoidoscopy can also be done with a colonoscope, which is longer and normally used for colonoscopy.
In Germany, sigmoidoscopy is not routinely used for bowel cancer screening. But because this method has been tested in trials and these trials also help to assess the benefit of the colonoscopy offered in Germany, we will present the results in this article.
2.2.1. The examination
Before you have a sigmoidoscopy you have to drink a laxative to cleanse the bowel. Another option is to empty the bowel by using an enema shortly before the procedure. The examination is rather short and only takes 5 minutes on average. You do not necessarily need sedatives or painkillers.
2.2.2. Advantages and disadvantages
About two thirds of all bowel cancers grow in the part of the bowel examined in a sigmoidoscopy. Other tumors cannot be found using this approach. During a sigmoidoscopy the doctor can remove polyps growing in the last section of the bowel that might turn into cancer.
If the doctor finds bowel cancer or polyps in a sigmoidoscopy, he or she usually recommends having a colonoscopy too.
There are four large trials looking at sigmoidoscopy examinations in the prevention of bowel cancer, three of which have been published: The most important one so far, a British trial with more than 170,000 men and women between the ages of 55 and 64, looked at whether a single sigmoidoscopy examination can effectively prevent bowel cancer. After 11 years, it was concluded that there was a benefit:
- About 5 out of 1,000 people who were not offered a sigmoidoscopy died of bowel cancer during this time.
- About 3 out of 1,000 people who were offered a sigmoidoscopy died of bowel cancer.
In other words: sigmoidoscopy could prevent 2 out of 1,000 people from dying of bowel cancer.
The examination also reduced the risk of getting bowel cancer:
- Without sigmoidoscopy, 16 out of 1,000 people got bowel cancer.
- With sigmoidoscopy, 12 out of 1,000 people got bowel cancer.
This means that sigmoidoscopy examinations prevented 4 out of 1,000 people from getting bowel cancer.
Another trial done in Italy with around 34,000 participants between the ages of 55 and 64 also showed that a single sigmoidoscopy examination can lower the risk of getting bowel cancer or dying of it. The amount of benefit was similar to the one found in the British trial.
The third trial published so far was done in Norway and included about 55,000 participants between the ages of 55 and 64. After seven years, this trial did not show clearly that sigmoidoscopy reduces the risk of bowel cancer. This does not necessarily contradict the results of the British and the Italian trial because the Norwegian trial probably has not lasted long enough to show a preventive effect of endoscopy of the bowel.
Adverse effects and complications
Pain is one of the most common adverse effects of a sigmoidoscopy. Without painkillers or sedatives about 18 out of 100 people have pain of medium severity during the procedure; just under 3 out of 100 people have more severe pain. Another common adverse effect is temporary flatulence (“gas”) after the examination. Also, the laxatives taken in preparation for the sigmoidoscopy might continue to cause diarrhea for several days afterwards.
Sigmoidoscopy carries a very small risk of complications such as severe bleeding and intestinal perforations. It is estimated that this kind of complication happens in up to 4 out of 10,000 sigmoidoscopies. It is not known how many bowel polyps are removed unnecessarily (because they would not have developed into cancer anyway).
A colonoscopy (also called coloscopy) is an examination of the entire large intestine with a special endoscope called a colonoscope (or coloscope). The colonoscope works like a sigmoidoscope, but it is longer so that the large bowel can be examined along its entire length of 1.5 meters. The colonoscope is inserted into the anus and slowly pushed through to where the large and the small bowel meet. Throughout the procedure the bowel is widened a little with air or carbon dioxide to make it easier for the doctor to see the inside of the bowel.
If polyps or abnormal parts of the mucous membrane are found during the endoscopy, they can also be removed through the endoscope with a small wire loop or forceps. If potentially cancerous tissue is found, tissue samples can be taken during the procedure and examined more closely in a laboratory.
2.3.1. The examination
Before you have a colonoscopy, your entire large bowel has to be completely empty. Because of this, preparing for a colonoscopy takes more time and effort than preparing for a sigmoidoscopy. It is helpful to avoid eating foods that are difficult to digest in the days leading up to the examination. There are different possibilities to prepare for the examination, but it is usually necessary not to eat any solid food at all in the 24 hours before the colonoscopy. On the day before the procedure, and sometimes on the day itself, you drink a laxative and a lot of fluid, until only a clear liquid comes out when you go to the toilet. Your doctor will tell you more details.
You can have painkillers and sedatives before the procedure so that you will not notice much of the examination. If you take a sedative, it is important not to drive a car or operate machinery afterwards. How long this is the case depends on the medications taken. Your doctor will give you more information. If you are in doubt, do not hesitate to ask. The procedure itself usually takes half an hour.
Sometimes an endoscopy of the bowel is stopped because it is too unpleasant. Also, it is not always possible to push the endoscope far enough to see the entire large bowel because of particular anatomic features. This problem is more common in people who have had abdominal surgery in the past because this can cause tissue to stick together in the abdominal cavity and make the intestinal loops more rigid.
2.3.2. Advantages and disadvantages
In a colonoscopy, the entire large bowel is examined for bowel polyps and possible cancerous tissue. Most bowel polyps and cancerous tumors can be found this way. Colonoscopy is the screening test for bowel cancer that takes the most time and effort. It also carries a higher risk of complications than sigmoidoscopy.
Despite the fact that the examination is fairly accurate, a bowel polyp or cancer can sometimes be overlooked in a colonoscopy. It is not known, on the other hand, how many bowel polyps are removed unnecessarily (because they would not have turned into cancer anyway).
Unlike the stool test and sigmoidoscopy, colonoscopy has not yet been tested in similarly conclusive trials. This makes it difficult to assess its advantages and disadvantages exactly. Although colonoscopy allows for the entire large bowel to be examined, this does not automatically mean that it offers better protection from cancer. Some experts believe that mainly flat cancerous tumors grow in those sections of the large bowel that can only be reached with a colonoscope. This kind of tumor is more easily overlooked than bowel polyps, which bulge out into the inside of the bowel and are clearly visible. However, it may be assumed that the benefit of a colonoscopy is at least as great as that of a sigmoidoscopy. Whether or not a colonoscopy can better prevent bowel cancer is not clear because both kinds of examination have not been compared directly in trials.
Adverse effects and complications
About 26 to 35 out of 10,000 people who have a colonoscopy have complications where further treatment becomes necessary. These include severe bleeding, which can mainly occur after removal of a polyp, or cardiovascular complications, which are then often a consequence of the sedative medications. Intestinal perforations can happen in very rare cases. According to different estimates, this serious complication happens in 3 to 8 out of 10,000 examinations. The overall risk of complications is higher in colonoscopy than in sigmoidoscopy.
So far there are no reliable data on the frequency of pain during a colonoscopy. Painkillers and sedatives are usually used because otherwise the examination can be unpleasant and painful. These drugs can have adverse effects.
2.4. What statutory health insurance pays for in Germany
In Germany, statutory health insurance funds cover the costs of two screening tests: all members of a statutory health insurance fund between the ages of 50 and 54 are entitled to a stool test once a year, and, if there are suspicious findings, to a colonoscopy. After the age of 55, they can choose between having a stool test every two years or a colonoscopy. They can have a total of two colonoscopies with at least 10 years between the two tests if the health insurance fund is to pay for them. If people have their first colonoscopy when they are 65 or older, they are not entitled to a second colonoscopy. Statutory health insurance funds do not cover the costs for screening tests using sigmoidoscopy, immunological tests and DNA stool tests.
If you have symptoms, however, you are always entitled to have them checked – no matter if and when you last had a screening.
3. Personal aspects
3.1. Feeling embarrassed
Many people find a bowel endoscopy unpleasant. As well as the extensive preparation involved and the adverse effects, embarrassment could be one reason not to have a screening test. It might help if the doctor is the same sex as you – or the other sex, if that is what you would prefer. The doctor can also give you sedatives and painkillers to make the procedure less unpleasant.
The stool test also puts some people off because they think it is disgusting or dirty, or because they are embarrassed to send the test card in the post. But there is no need to worry about this: the test cards can be sealed so that they are clean and do not smell.
3.2. Bowel cancer in the family
Like other conditions affecting the bowel and stomach, bowel cancer is often considered a taboo subject that people do not like to talk about or think about. Because of this, some people might not be aware that a close relative of theirs has bowel cancer. But this information can be very important for deciding whether to have a screening or not: people who have first degree relatives with bowel cancer have a higher risk of developing bowel cancer themselves. IQWiG is currently doing research on the question of whether this has a particular impact on screening. Other people with relatives who are affected, on the other hand, might avoid screening tests exactly because they are afraid that doctors might find something abnormal. Yet screening offers a chance to prevent bowel cancer from developing.
3.3. Making a decision
It is true of all screening tests that only a few of the people taking them will benefit. This is in the nature of things because from an individual person’s point of view the risk of getting bowel cancer or even dying of it within a few years is relatively low. But because bowel cancer can have serious consequences, screening can still be worthwhile for the individual person. People have to decide for themselves: some people find the advantages of the screening more important, others see more disadvantages.
Looking at the advantages and disadvantages of the examinations and at the time and effort they involve, it is not surprising that different people make different decisions. Bowel cancer screening offers a chance to prevent bowel cancer. Whether or not someone regards the risk of getting bowel cancer as threatening is an individual matter. There might be other things you find more important regarding your health.
There is no need to make your decision in favor of or against a screening test under pressure. You can take your time to decide whether or not you would like to have one.
If you decide to have a screening test, remember that none of the tests can guarantee that you will not get ill. It is still important to take any symptoms seriously, even if there were no abnormal findings in your last screening test.
Author: Institute for Quality and Efficiency in Health Care (IQWiG)
Next planned update: December 2014. You can find out more about how our health information is updated here (URL: http://www.informedhealthonline.org/our-methods.643.en.html?bab[subpage_id]=0-8) .
IQWiG health information is based on research in the international literature. We identify the most scientifically reliable knowledge currently available, particularly what are known as “systematic reviews”. These summarize and analyze the results of scientific research on the benefits and harms of treatments and other health care interventions. This helps medical professionals and people who are affected by the medical condition to weigh up the pros and cons. You can read more about systematic reviews and why these can provide the most trustworthy evidence about the state of knowledge here (URL: http://www.informedhealthonline.org/here.61.en.html) . We also have our health information reviewed to ensure the medical and scientific accuracy of our products.
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