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Bowel cancer: Overview

Last Update: June 28, 2016; Next update: 2019.


Bowel cancer is one of the more common forms of cancer many countries including Germany. Bowel cancer usually refers to cancer of the large intestine (large bowel). Cancer in the small intestine is very rare.

Bowel cancer almost always develops from growths called polyps that form along the lining of the large intestine. But not all polyps will cause cancer – and if they do, the process can take many years. One way to prevent bowel cancer is to have a colonoscopy that will also enable doctors to remove the polyps.

Having bowel cancer can be a life-changing experience. The stage the cancer is at will largely determine what happens after a diagnosis has been made. For early-stage bowel cancer, the tumor just needs to be surgically removed. At advanced stages additional treatments may be an option, such as chemotherapy or radiation therapy.

In Germany, high-quality medical care is available for people who have cancer. There are also a number of different ways of getting support to help cope with the disease emotionally and make transition back to the workplace easier.


Bowel cancer often does not cause any symptoms at first, so it may remain unnoticed for a while, but sometimes it may lead to abdominal pain or irregular bowel movements. This means that the frequency of bowel movements or their usual time may change. These symptoms also include constipation or diarrhea. Black or very dark stool may be a sign of blood traces and is also a sign of bowel cancer. When bowel cancer has reached a more advanced stage it can also cause weight loss, nausea and loss of appetite.

It's important to keep in mind that these symptoms could have any number of other causes. Most of the time there is no serious underlying condition or the symptoms may suggest another, non-cancerous health problem, such as enlarged hemorrhoids or an inflammation of the bowel.


Bowel cancer is caused by cells in the mucous lining of the intestine changing and then multiplying out of control. This growth pushes the cells into surrounding tissue. There are a number of possible causes of these kinds of changes, including pollution or radiation. Often they simply occur by chance. Normally the body’s immune system can deal with these malignant cells, but not always. As we grow older, mistakes in cell division increase while the body’s ability to repair these problems decreases. This is why most types of cancer are more common in older people.

Most people who have bowel cancer can't find a clear cause. About 5 out of 100 people with bowel cancer have a genetic form. This could either be familial adenomatous polyposis (FAP) or hereditary nonpolyposis colorectal cancer (HNPCC). These two types are more likely to start at a younger age.

Risk factors

There are factors that can slightly increase the risk of developing bowel cancer. People who have chronic inflammatory bowel conditions such as Crohn's disease and ulcerative colitis are at greater risk of getting bowel cancer. If first-degree relatives have had bowel cancer, the risk for bowel cancer is slightly higher too. First-degree relatives are parents, siblings and children.


The risk of bowel cancer also increases with age: Many people who have bowel cancer are already over 75 years old. Bowel cancer is very rare in anyone under the age of 50.

Bowel cancer is sometimes considered to be a disease that typically affects men, but this is wrong. It is more common in men and often starts at an earlier age, but women can also develop bowel cancer.

The following tables show the probabilities of getting bowel cancer within the next ten years for people of a certain age. These are averages for specific age groups – everyone also has their own personal risk factors.

Table: Risk of bowel cancer in men

AgeNumber of men who develop bowel cancer in the next ten yearsNumber of men who will die of bowel cancer in the next ten years
507 out of 1,0002 out of 1,000
5513 out of 1,0004 out of 1,000
6018 out of 1,0006 out of 1,000
6524 out of 1,0009 out of 1,000

Table: Risk of bowel cancer in women

AgeNumber of women who develop bowel cancer in the next ten yearsNumber of women who will die of bowel cancer in the next ten years
505 out of 1,0001 out of 1,000
558 out of 1,0002 out of 1,000
6010 out of 1,0003 out of 1,000
6514 out of 1,0005 out of 1,000


Bowel cancer develops gradually over a period of many years. Non-cancerous (benign) growths in the mucous lining of the bowel are the first stage, which isn't yet considered dangerous. These growths are referred to as polyps or adenomas. Some of them grow like wart-like small mounds, while others look somewhat like small stemmed mushrooms. With advancing age, bowel polyps become increasingly common. About one third of all adults over the age of 55 have at least one bowel polyp.

The great majority of these polyps stop growing and don't pose any threat. But many continue growing for several years, and some turn malignant.

If a polyp turns malignant, there's a risk that the cancerous cells grow deeper into the wall of the bowel. If the tumor continues to grow, it's possible that it could reach other organs, such as the liver. When the cancer cells spread further like that, it's called “metastasis.” There are a number of different factors that will influence how the cancer develops. The prognosis is good when a smaller, localized, early-stage tumor is removed: Most people then recover fully after surgery. When the cancer is more advanced, the chances of complete recovery drop. And if metastasis has already started, recovery is usually not expected. In that case treatment aims to slow tumor growth and to help maintain a good quality of life for as long as possible.

It usually takes about five years to know if the cancer is completely gone. The chances of the cancer coming back depend on its stage at the time it was treated.


If your doctor thinks you may have bowel cancer, a colonoscopy is usually done first. A specialized endoscope is used to examine the entire large intestine. Tissue samples can be taken and tested for cancer in a laboratory. Usually the results are back a few days later. Sometimes it's not possible to examine the entire intestine using an endoscope – the passage may be constricted or there may be tissue blocking the way. In that case, computed tomography (CT) or magnetic resonance imaging (MRI) can be used to examine the bowel.

There are different ways of testing whether the cancer has already spread beyond the bowel, including abdominal ultrasound, x-ray of the torso and a digital rectal examination. If your doctor thinks there are signs of metastasis, other tests can be performed to gather more information, such as a CT of the abdomen or chest.

Blood is also taken before treatment starts to test it for a specific tumor marker called carcinoembryonal antigen (CEA). This test is helpful for estimating the chances that treatment will be successful.

Positron emission tomography is also used sometimes if bowel cancer comes back again following treatment.


Health insurers in Germany offer two types of bowel cancer screening:

  • Testing for blood in the stool: This is covered by German statutory health insurers for men and women over the age of 50.
  • Colonoscopy for endoscopic examination of the large intestine: Existing polyps can be removed during this exam. Publicly insured people in Germany can have two free colonoscopies: the first after the age of 55, and the second 10 years later. In other health care systems, the options will be different. If polyps are removed during the first colonoscopy, it's usually recommended to repeat the examination sooner.

The general rule is: whoever has symptoms always has access to a free diagnosis – regardless of whether (or when) you've already had screening for the condition.

A third possibility for screening is having a sigmoidoscopy. In Germany, though, this test isn't covered by statutory health insurers when performed for screening.


Early-stage cancer can be detected using colonoscopy. Because polyps can be removed at the same time as the examination, it also serves as prevention. But even a colonoscopy can't offer a 100% guarantee of preventing bowel cancer.

There are a lot of recommendations about general bowel cancer prevention: These include getting enough exercise, eating a lot of fruits vegetables and fiber, and avoiding red meat and alcohol. But none of this advice has ever been scientifically proven to be able to prevent bowel cancer.

Some studies have already tested whether the long-term use of drugs like ASA (the drug in “Aspirin”) can prevent bowel cancer. These drugs are not recommended because it isn't clear that they actually prevent bowel cancer, while at the same time they can cause side effects.


Surgery is used to remove as much of the cancer as possible. In some cases, no further treatment may be needed for early-stage tumors. If the cancer is at a more advanced stage, treatments like chemotherapy or radiation therapy are options.

Everyday life

Even successful treatment of bowel cancer is often followed by a period of uncertainty because you can only be sure years later that the cancer is gone for good.

Advanced bowel cancer can have a major effect on your quality of life. Many people feel weak for quite some time after treatment and may not be as active as they'd been before. It takes time to come to terms with the diagnosis and the therapy and its effects.

If the rectum has also been affected by cancer and needs surgery, it isn't always possible to retain the sphincter muscle. In that case an artificial opening (stoma) is needed for the bowel. It can take some time to get used to not being able to fully control bowel movements and having an artificial opening. Many people feel embarrassed about it at first, and may start avoiding others.

Although having bowel cancer can really turn things upside down, over time many people find a way to cope and still manage to live the life they want.


  • Deutsche Gesellschaft für Gastroenterologie, Verdauungs- und Stoffwechselkrankheiten (DGVS). S3-Leitlinie Kolorektales Karzinom. June 2013 (AWMF Leitlinien; Band 021-007OL).
  • Robert Koch-Institut (ed.) und die Gesellschaft der epidemiologischen Krebsregister in Deutschland e.V. (ed.). Krebs in Deutschland 2005/2006. Häufigkeiten und Trends. Berlin: 2010.
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    Because IQWiG is a German institute, some of the information provided here is specific to the German health care system. The suitability of any of the described options in an individual case can be determined by talking to a doctor. We do not offer individual consultations.

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