Bowel cancer

Bowel cancer, also known as colorectal cancer, is a cancer that affects any part of the colon (large intestine) or rectum. It is one of the commonest forms of cancer.

Most bowel cancers start as a polyp on the lining of the bowel – polyps are like small spots or cherries on a stalk, and most do not cause any symptoms. 

Polyps are more common as we get old and most polyps are not pre-cancerous. One type of polyp however, called an adenoma can become cancerous. Most polyps remain benign throughout life, but about one in ten will turn into a cancer. Polyps are usually present for at least 10 years before becoming cancerous. The larger a polyp is, the more likely it is to become cancerous, usually once the polyp is larger than 1cm. We believe therefore that removing benign polyps at the time of a colonoscopy can prevent cancer from developing later.

What are the symptoms of bowel cancer?

The development of a bowel cancer from a polyp may take many years and early on there may be no symptoms at all. The most common symptoms are bleeding from the bowel, a change in bowel habit, such as unusual episodes of diarrhoea or constipation, or an increase in the amount of mucus in the stool. A bowel cancer can enlarge so that it partially or completely blocks the bowel leading to abdominal pain, constipation and bloating.

Sometimes tiny amounts of bleeding may go unnoticed but result in the development of anaemia which may cause tiredness and a decreased ability to work and exercise. 

Some of these symptoms are similar to irritable bowel. Therefore people with the following symptoms for more than 3 weeks should see their doctor:

  • Bleeding from the back passage
  • A change in bowel habit with either constipation or diarrhoea
  • Abdominal pain, especially if severe
  • A lump in the abdomen
  • Unexpected weight loss
  • Unexplained tiredness (as a sign of anaemia) 

What investigations are usually undertaken?

  • A careful history and examination is taken. Patients will often have:
  • Blood tests – to look for evidence of anaemia
  • Colonoscopy – a flexible telescope is passed through the anus into the rectum and examines the whole colon

At the time of colonoscopy, if polyps are identified these can usually be removed at the time of the procedure and sent off to the laboratory to look under the microscope.

If a cancer is diagnosed at the time of the colonoscopy, you will be advised to have blood tests and scans to determine what is known as the stage (extent) of the cancer. Not only will the size of the primary tumour be assessed as fully as possible but the specialist will also want to know if there is any sign of secondary spread. Armed with all the relevant information about the cancer, the specialists will decide how best to advise you on the most appropriate treatment.