A cancerous tumour of the lining of the colon or rectum
- Rare under the age of 40; becomes increasingly common over the age of 40
- Rectal cancer is more common in males; colon cancer is equally common in males and females
- In some cases, the condition is inherited
- A high-fat, low-fibre diet, alcohol abuse, and obesity are risk factors
Colorectal cancer is one of the most common cancers in the UK and is the second leading cause of cancer death (after lung cancer). However, it is one of the few cancers that can be detected early by screening people who are at risk (see Screening, and Colonoscopy), and when it is detected early enough, it can be treated successfully by surgery.
Colorectal cancer is rare under 40 and most often occurs in people over 60. Rectal cancer tends to be more common in men, while colon cancer affects men and women equally. Cancer can occur anywhere in the colon or rectum, but about 6 in 10 tumours develop in the lower third of the colon nearest the rectum.
What are the causes?
In less affluent countries, where people traditionally live on a high-fibre diet consisting mainly of cereals, fruit, and vegetables, colorectal cancer is rare. However, a typical Western diet, which tends to be high in meat and animal fats and low in fibre, seems to increase the risk of developing colorectal cancer. It is not known how fibre in the diet reduces the risk of the disorder. A possible explanation is that dietary fibre shortens the time that it takes for waste matter to pass through the intestines. As a result, potentially cancer-causing substances (known as carcinogens) in food are expelled from the body at a faster rate. Other lifestyle factors, such as excessive alcohol consumption, obesity, and lack of exercise, may also contribute to the risk of developing colorectal cancer. The reasons for this increased risk are also unknown.
About 1 in 8 cases of colorectal cancer is hereditary. Most of these cases are caused by inheritance of an abnormal gene. Some genetic abnormalities increase the risk of developing a form of the cancer known as hereditary nonpolyposis colorectal cancer (HNPCC). Rarely, colorectal cancer may be caused by the inherited disorder familial adenomatous polyposis (FAP), in which polyps (growths of tissue) form inside the large intestine (see Polyps in the colon). In FAP, there is a 9 in 10 chance that some of the polyps will become cancerous before the age of 40.
Inflammatory disorders affecting the large intestine, such as ulcerative colitis or Crohn’s disease, can also increase the risk of developing colorectal cancer if they are long-standing and most of the colon is affected.
What are the symptoms?
The symptoms of colorectal cancer vary depending on the site of the tumour. They may include the following:
Changes in the frequency of bowel movements or in the general consistency of the faeces.
Blood in the faeces.
Rectal discomfort or a sensation of incomplete emptying of the rectum.
Loss of appetite.
The symptoms of colorectal cancer may be mistaken for the symptoms of a less serious disorder, such as haemorrhoids. If there is heavy loss of blood from the rectum, iron-deficiency anaemia may result. This condition produces symptoms such as pale skin, headaches, and tiredness. As the tumour grows bigger, it may eventually cause intestinal obstruction.
You should consult your doctor promptly if you notice blood in your faeces or an inexplicable change in your bowel habits (such as increased frequency, loose stools, or diarrhoea), especially if you are over 50. Left untreated, colorectal cancer will eventually spread via the bloodstream to the lymph nodes, liver, and other organs in the body.
How is it diagnosed?
Colorectal cancer may be diagnosed during screening before symptoms have developed. If you do have symptoms, your doctor may feel your abdomen to detect any swelling and carry out a rectal examination, in which a gloved finger is inserted into the rectum to feel for a tumour. A stool sample is tested for the presence of blood and a blood sample is tested for evidence of anaemia.
The rectum may be examined visually with a viewing instrument inserted through the anus. Your doctor may also arrange for a colonoscopy, in which a flexible viewing instrument is used to examine the entire colon. A biopsy, in which a sample of intestinal tissue is removed for microscopic examination, may be performed during the procedure. You may also have a “virtual colonoscopy”, in which CT scans are used to produce a three-dimensional image of your colon or rectum in order to identify abnormal areas. Alternatively, and less commonly, a contrast X-ray with a barium enema may be used for the same purpose. If a cancerous tumour is detected, you will probably need to have CT scanning to see if the cancer has spread to the lymph nodes in the abdomen or to the liver or lungs. An MRI scan may also sometimes be done to help plan surgical treatment.
In the UK, screening with the faecal occult blood test is available for older age groups and people at high risk to detect colorectal cancer at an early stage.
What is the treatment?
Treatment of colorectal cancer depends on the site of the tumour. In most cases of early cancer, the affected part of the intestine can be removed and the cut ends rejoined (see Colectomy). In a few cases, if most of the rectum has been removed, a permanent colostomy may be necessary. In this procedure, an opening is created on the surface of the abdomen for the discharge of faeces. In some cases when the tumours are small and at an early stage, it may be possible to remove them by laparoscopic (“keyhole”) surgery. If the cancer cannot be cured, treatment is aimed at relieving the symptoms. For example, surgery may be done to remove a tumour obstructing the bowel. If cancer has spread to other parts of the body, chemotherapy, radiotherapy, or both may be necessary to treat the disease. Chemotherapy and/or radiotherapy may also be used to shrink large tumours before surgery.
About 9 in 10 people treated at an early stage live at least 5 years. Surgical removal of affected tissue at a more advanced stage of the disease gives the person a 3 in 4 chance of living at least 5 years. If the cancer has spread, the outlook is less favourable.
From the 2010 revision of the Complete Home Medical Guide © Dorling Kindersley Limited.
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