Find information on how we’re keeping you safe from COVID-19 here

To top

Bowel Cancer

What is Bowel Cancer?

The ‘large bowel’ is made up of the colon and rectum. Cancer that grows in the large bowel is known as bowel cancer and it effects 1 in 20 people. Most bowel cancers develop from pre-cancerous growths, called polyps. Not all polyps develop into cancer, but the identification and removal of polyps can reduce your risk of bowel cancer.

Bowel cancer is the fourth most common cancer in the UK and the second biggest cause of cancer related deaths. Survival from bowel cancer is greatly improved by its early detection.

bowel cancer diagram

What Causes Bowel Cancer?

Some bowel cancers occur because of inherited genetic conditions. This is known as Familial Adenomatous Polyposis or Lynch Syndrome which is also known as hereditary non-polyposis colorectal cancer (HNPCC). However, these only account for about 5% of all bowel cancers, although 25% of bowel cancers have some familial link. The risk of bowel cancer is greater if you have more than one family member or close relative that has bowel cancer.

The majority occur spontaneously in the bowel. This is known as ‘sporadic’ cancer and it is typicaly diagnosed in people over the age of 50. In recent years, the rates of bowel cancer diagnosed in people under the age of 50 have been increasing, but we do not fully understand at the moment why this trend is occurring.

There are several risk factors that may increase a person’s risk of bowel cancer. These include:

Low-fibre, high-fat diet. Diet which is low in fibre and high in fat and calories, typically associated with a Western diet, may increase the risk of bowel cancer. Some studies have found an increased risk of colon cancer in people who eat diets high in red meat and processed meat.

A sedentary lifestyle. A person who is inactive is more likely to develop bowel cancer.

Diabetes. A person with diabetes or insulin resistance carries a lightly higher risk of bowel cancer.

Obesity. An obese person has an increased risk of bowel cancer and an increased risk of dying of colon cancer when compared with people considered normal weight.

Smoking. A person who smokes may have an increased risk of bowel cancer.

Alcohol. Heavy use of alcohol increases a person’s risk of bowel cancer.

Radiation therapy for cancer. Radiotherapy directed at the abdomen and pelvis to treat other types of cancers predisposes the risk of that person to a higher risk of bowel cancer.

Inflammatory bowel conditions. Long standing chronic inflammatory diseases of the large bowel, such as ulcerative colitis and Crohn’s disease, also increases the risk of bowel cancer.

What are the Symptoms of Bowel Cancer?

Many people with bowel cancer do not have any symptoms in the early stages of their disease. The types of symptoms that appear are variable and depend on the location and size of the cancer in the large bowel. Therefore if there is any doubt, your doctor may perform diagnostic tests such as a colonoscopy.

Some signs and symptoms of bowel cancer include:

  • A persistent change in your bowel habits, including diarrhoea or constipation or a change in the consistency of your stool
  • Rectal bleeding
  • Persistent abdominal discomfort, such as cramps, gas or pain
  • A sensation of incomplete emptying of your bowel
  • Weakness or fatigue
  • Unexplained weight loss

How is Bowel Cancer Diagnosed?

If your signs and symptoms warrant exclusion of bowel cancer, one or more investigations are required:

Faecal tests: Your family doctor may perform an analysis of the stool to identify the presence of blood, and this can be done at home. This is known as a Faecal Immunochemical Test (FIT test). The previous test used to screen for colon cancer was called the Faecal Occult Blood Test (FOBT). Recent studies have shown that FIT is more accurate for the diagnosis of CRC than FOBT. This is because it is more specific for bleeding from the colon as opposed to the stomach or the small bowel, and its accuracy is not affected by diet or medications. FIT also offers some significant advantages over this test. For example, it only requires one stool sample and the analysis can be automated. The test is also more objective and reproducible.

Blood tests: At present, no blood test can reliably diagnose bowel cancer. Some patients with bowel cancer may present with anaemia, and your doctor may want to check this. A chemical produced by bowel cancer cells called carcinoembryonic antigen, or CEA. This test is not reliable in the diagnosis of bowel cancer but its level in the blood may help provide information that guides treatment.

Colonoscopy: A colonoscopy is the gold standard test used to investigate for bowel cancer. It is a specialised examination that involves using a long, thin and flexible tube to examine the lining of the large bowel.  The tip of the tube has a video camera attached to it that provides real time views of the large bowel.  If there are any suspicious areas encountered, a tissue sample (biopsy) can be obtained for analysis in the laboratory for diagnosis. A colonoscopy is also often performed to confirm abnormalities detected on other forms of investigations such as double-contrast barium enema (DCBE) and CT virtual colonoscopy (CT pneumocolon) and to obtain biopsy for diagnosis.

Flexible sigmoidoscopy: This is similar to colonoscopy, in that the bowel is inspected with a flexible camera. But there are some important differences. Firstly, you will not be required to have bowel preparation and you will receive an enema on the day of the test. Secondly, the test only examines the left side of the bowel. This means the test is less invasive, and most patients will not require sedation.

CT virtual colonoscopy: Increasingly, CT scans are being used to diagnose bowel cancer. Unlike a normal CT scan, this test requires you to have a bowel cleansing medicine so that small lesions can be identified more clearly. During the test you will be asked to lie on your front, and a small tube will be inserted into the bottom. This allows some air to be inserted into the colon so that the colon can be inflated with air. This allows the radiologist to identify small polyps. The benefit of this test is that you will not require sedation and it is less invasive than colonoscopy. The risk of this diagnostic approach is that if a polyp or cancer is identified you will need to undergo a colonoscopy.

If a cancer is diagnosed you many need to undergo some further specific investigations to help guide treatment. The doctor will help explain these to you, however the goal will be to determine if the cancer has spread. This is known as “staging” the cancer.

How is Bowel Cancer Treated?

The type of treatment that is required depends on the location of the bowel cancer, its stage and the general health of the patient. In general, treatment for bowel cancer usually involves surgery to remove the segment of the bowel that contains the cancer. Other treatments, such as radiotherapy and chemotherapy, may also be needed.


If the bowel cancer is very small and it is in its early stage, it may be possible to remove it with colonoscopy using special tools that incorporates a small amount of the inner lining of the bowel with the polyp in a procedure called endoscopic mucosal resection (EMR).

Larger cancerous polyps or cancers that cannot be removed during colonoscopy may be removed using a minimally invasive surgery approach called laparoscopic surgery (also known as key-hole surgery). In this procedure, the surgeon will perform the operation throughout several small incisions in the abdominal wall. Using laparoscopic instruments and cameras that display the bowel on a live video monitor, the surgeon will remove the part of your bowel that contains the cancer, along with its lymph nodes and a margin of normal tissue on either side of the cancer. The surgeon is often able to reconnect the healthy parts of the bowel without the need to create a stoma. This requires admission to hospital and it cannot be performed as a day surgery operation.

When it is not possible to reconnect the healthy portions of your bowel, a stoma may need to be created. This involves creating an opening in the wall of your abdomen from a portion of the remaining bowel to allow the stool to empty into a bag that fits securely over the opening. The stoma is sometimes temporary, allowing the bowel some time to heal after surgery. In some cases, however, the stoma may be permanent.

If the bowel cancer is very advanced or if the patient’s general health is very poor, an operation to relieve a blockage of the bowel in order to improve the symptoms may be appropriate. This type of operation is performed to provide relief for signs and symptoms related to the blockage or for pain but it is not performed to cure the underlying bowel cancer.


Chemotherapy involves the use of powerful drugs to destroy the cancer cells. This is often given after surgery when the cancer is found to be large or if it has spread to the lymph nodes.  The rationale behind this is to use these powerful drugs to destroy any remaining cancer cells in the body and it may help reduce the risk of the cancer coming back. Chemotherapy may also be used before an operation to reduce the size of a large cancer so that it is easier to remove during surgery. It may be combined with radiotherapy to achieve the desired effect. Chemotherapy can also be used to relieve symptoms of bowel cancer that cannot be removed with surgery or in situations whereby the cancer cells have spread to other parts of the body.


Radiotherapy treatment involves the use of power energy sources, such as high energy x-ray beams or other types of radiation, to cause physical and chemical damage to destroy cancer cells. It is sometimes used to shrink the size of a large cancerous mass before surgery so that it can be removed easily or in its entirety.  When surgery is not an option, radiotherapy may be provided to relieve symptoms such as pain and bleeding. Radiotherapy is sometimes combined with chemotherapy to achieve a stronger response to treatment.

Targeted drug therapy and immunotherapy

Targeted drug treatments are powerful drugs that focus on specific abnormalities displayed by the cancer cells. The aim of this type of therapy is to block these abnormalities from being expressed by the cancer cells thereby causing these cells to die. It is often administered in combination with chemotherapy. Immunotherapy on the other hand is a type of drug treatment that uses the person’s immune system to destroy cancer cells. Cancer cells often produce proteins that prevent that person’s immune system from recognising them. Immunotherapy interferes with that process and facilitates the body recognising these cancer cells to destroy it. At present, both targeted drug therapy and immunotherapy are reserved for those diagnosed at the advanced stage of bowel cancer.

Palliative treatment

Palliative care is a highly specialised branch of medicine that focuses on providing relief from pain and other symptoms related to the underlying bowel cancer. It is provided by a team of doctors, nurses and other specially trained professionals to improve the quality of life for people with cancer and their families. It is often used alongside other appropriate treatments with the aim of making the patient feel better and live longer.