Colorectal (Bowel) Cancer

bowel cancer

The colon and rectum are parts of the gut (gastrointestinal tract). When we eat or drink the food and liquid travel down the esophagus into the stomach. The stomach then passes it into the small intestine. The small intestine is several meters long and is where food is digested and absorbed. Undigested food, water and waste products are then passed into the large intestine. The main part of the large intestine is called the colon, which is about 150 cm long. This is split into four sections: the ascending, transverse, descending and sigmoid colon. Some water and salts are absorbed into the body from the colon. The colon leads into the rectum (back passage), which is about 15 cm long. The rectum stores feces (stools) before they are passed out from the anus.

What is colorectal cancer?

Colorectal cancer is a cancer of the colon or rectum. It is sometimes called bowel cancer or cancer of the large intestine. It is one of the most common cancers. Colorectal cancer can affect any part of the colon or rectum. However, it most commonly develops in the lower part of the descending colon, the sigmoid colon, or rectum.
Colorectal cancer usually develops from a polyp which has formed on the lining of the colon or rectum. As the cancer cells multiply they form a tumor. The tumor invades deeper into the wall of the colon or rectum. Some cells may break off into the lymph channels or bloodstream. The cancer may then metastasize (spread) to lymph nodes nearby or to other areas of the body - most commonly, the liver and lungs.

Polyps and colorectal cancer

A bowel polyp (adenoma) is a small growth that sometimes forms on the inside lining of the colon or rectum. Most bowel polyps develop in older people. Polyps are benign (noncancerous) and usually cause no problems. However, sometimes a benign polyp can turn cancerous.

Risk factors

  • Ageing. Colorectal cancer is more common in older people. Eight out of ten people who are diagnosed with colorectal cancer are older than 60 years.
  • If a close relative has had colorectal cancer (there is some genetic factor).
  • If you have familial adenomatous polyposis or hereditary non-polyposis colorectal cancer.
  • If you have ulcerative colitis or Crohn's disease for more than 8-10 years.
  • Obesity.
  • Lifestyle factors: little exercise, drinking a lot of alcohol and eating lot of red meat.

Protective factors

  • Women who take hormone replacement therapy (HRT).
  • People who eat a lot of fruit and vegetables.
  • People on aspirin. Several recent research studies have found that taking aspirin each day reduces the risk of developing colorectal cancer.

What are the symptoms of colorectal cancer?

  • When a colorectal cancer first develops and is small it usually causes no symptoms.
  • Bleeding from the tumor. You may see blood mixed up with your feces (stools or motions). Sometimes the blood can make the feces turn a very dark color. The bleeding is not usually severe and in many cases it is not noticed, as it is just a small trickle which is mixed with the feces.
  • Passing mucus with the feces.
  • A change from your usual bowel habit. This means you may pass feces more or less often than usual.
  • A feeling of not fully emptying the rectum after passing feces.
  • Abdominal pains.

As the tumor grows in the colon or rectum, symptoms may become worse and can include:

You may feel generally unwell, tired or lose weight. If the cancer becomes very large, it can cause a blockage (obstruction) of the colon. This causes severe abdominal pain and other symptoms such as vomiting. Sometimes the cancer makes a hole in the wall of the colon or rectum (perforation). This causes severe pain. If the cancer spreads to other parts of the body, various other symptoms can develop.

How is colorectal cancer diagnosed and assessed?

Initial assessment

If a doctor suspects that you may have colorectal cancer, he or she will examine you. The examination will usually include a rectal examination where a doctor inserts a gloved finger through your anus into your rectum to feel if there is a tumor in the lower part of the rectum.


Colonoscopy is a test in which a long, thin, flexible telescope (a colonoscope) is passed through your anus into your rectum and colon. This enables the whole of your colon and rectum to be visualised in detail.

Flexible sigmoidoscopy. This is similar to colonoscopy. The difference is that a shorter telescope is used which is inserted only into the rectum and sigmoid colon.

CT colonography. This test uses X-rays to build up a series of images of your colon and rectum. A computer then organises these to create a detailed picture that may show polyps or anything else unusual on the surface of your colon or rectum.

Barium enema. This X-ray test obtains pictures of your colon and rectum. Barium liquid is placed in the colon and rectum, and the outline of the colon and rectum shows up clearly on X-ray pictures. This test is not done so much since colonoscopy became available.


If you have a colonoscopy or sigmoidoscopy, the doctor or nurse can take a biopsy of any abnormal tissue. This is done by passing a thin grabbing instrument down a side channel of the colonoscope or sigmoidoscope. It can take up to two weeks for the result of a biopsy.

Assessing the extent and spread

If you are confirmed to have colorectal cancer, further tests may be done to assess if it has spread. For example, a CT scan, an MRI scan, ultrasound scan. This assessment is called staging of the cancer. The aim of staging is to find out:

  • How much the tumor in the colon or rectum has grown?
  • Whether the cancer has spread to local lymph nodes.
  • Whether the cancer has spread to other areas of the body.

By finding out the stage of the cancer, it helps doctors to advice on the best treatment options. It also gives a reasonable indication of outlook (prognosis).
A common staging system for colorectal cancer is called the Dukes' classification:

  • Duke A: the cancer is just in the inner lining of the colon or rectum.
  • Duke B: the cancer has grown to the muscle layer in the wall of the colon or rectum.
  • Duke C: the cancer has spread to at least one lymph node near the colon or rectum.
  • Duke D: the cancer has spread to other parts of the body (metastases or secondary tumours). The most common site for colorectal cancer to spread to is the liver. Other places include the lungs and brain.

What is the treatment for a bowel polyp?

If a polyp is found during a colonoscopy (or sigmoidoscopy) it can often be easily removed as described above.

Some polyps contain cancer cells. If these cells are confined to within the polyp then the removal of the polyp is curative. If the cells look as if they had begun to spread to the wall of the colon or rectum then an operation may be needed to remove that section of colon or rectum.

What are the treatment options for colorectal cancer?

Treatment options that may be considered include surgery, chemotherapy and radiotherapy. The treatment advised for each case depends on various factors such as the stage of the cancer (how large the cancer is and whether it has spread), and your general health.

Treatment may aim to cure the cancer. Some colorectal cancers can be cured, particularly if they are treated in the early stages of the disease. If you are in remission, you may be cured. However, in some cases a cancer returns months or years later.

Treatment may aim to control the cancer. If a cure is not realistic, with treatment it is often possible to limit the growth or spread of the cancer so that it progresses less rapidly.

Treatment may aim to ease symptoms. If a cure is not possible, treatments may be used to reduce the size of a cancer, which may ease symptoms such as pain.


Removing the tumor may be curative if the cancer is in an early stage. The common operation is to cut through the colon or rectum above and below the tumor. The affected section is then removed and, if possible, the two cut ends are sewn together.

Sometimes a temporary colostomy is done to allow the joined ends to heal without feces passing through. The colostomy is often reversed in a second operation a few months later when the joined ends of the colon or rectum are well healed.

If the tumor is low down in the rectum, then the rectum and anus need to be removed. You would then need a permanent colostomy.

A colostomy is where an opening (hole) is made through the wall of the abdomen. A section of colon is then cut and the edges are attached to the opening in the abdominal wall. This is called a stoma and it allows feces to pass out from the colon into a disposable bag which is stuck over the stoma.

Chemotherapy and radiotherapy

Chemotherapy is a treatment of cancer by using anti-cancer medicines which kill cancer cells or stop them from multiplying. Chemotherapy is increasingly being used for people with colorectal cancer.

Radiotherapy is a treatment which uses high-energy beams of radiation which are focused on cancerous tissue. This kills cancer cells, or stops cancer cells from multiplying. It is most commonly used for colorectal cancer when the tumor is in the rectum.

When chemotherapy or radiotherapy is used in addition to surgery it is known as adjuvant chemotherapy or adjuvant radiotherapy.

What is the prognosis?

There has been a substantial improvement in the prognosis of people with colorectal cancer over the past decade.  People diagnosed at an early stage (stage A) have more than a 9 in 10 chance of surviving the disease.

If the cancer is diagnosed when it has grown through the wall of the colon or rectum, or spread to other parts of the body, there is less chance of a cure.

Screening for colorectal cancer

A simple screening test for colorectal cancer, which tests for traces of blood in the feces, has recently been introduced in the developed countries. This colorectal / bowel cancer screening test is to be offered to all people of certain older ages. In addition, some younger people may be offered screening if they have a higher-than-average risk of developing colorectal cancer.

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