Symptoms and Diagnosis of Bowel and Colon Cancer
Bowel Cancer and Colon Cancer Symptoms
Because early cancers often cause no symptoms, screening of symptom-free individuals for colon cancer and bowel cancer is being considered. About 85 per cent of people with bowel cancer are currently not diagnosed until the cancer has penetrated through the bowel wall or spread to lymph nodes or elsewhere. Some of the symptoms include:
- Bleeding from the back passage.
- Loss of the normal form of bowel motions sometimes followed by diarrhoea.
- Constipation can also occur.
- If the growth starts to block the bowel then colicky lower abdominal pain (i.e. coming in waves each of which lasts for a few minutes) can develop.
- If the bowel becomes completely obstructed, severe abdominal pain and vomiting occurs, followed by complete constipation.
In the proximal colon, the lumen is larger (about 4 or 5cm in diameter) and less likely to become obstructed. Cancers of this part of the colon, including the caecum, tend to show themselves very subtly as iron-deficiency anaemia, due to loss of small amounts of blood over a long period of time. The anaemia can lead to symptoms of pallor, shortness of breath or simply tiredness. Cancers of the rectum typically cause rectal bleeding, which can easily be mistaken for bleeding haemorrhoids (piles). Other symptoms include the feeling of not fully empting the bowel accompanied by a need to frequently empty the bowel. Loss of appetite and weight loss tend to be late features in bowel cancer.
Bowel and Colonic Cancer Diagnosis
Cancer of the rectum can be felt by inserting a gloved finger into the rectum. The diagnosis should usually be confirmed by biopsy in which a small (2mm diameter) sample of tissue is taken painlessly with forceps inserted through a small tube (a proctoscope or sigmoidoscope).
To spot cancers further along the colon, a sigmoidoscopy or colonoscopy may be performed using either a flexible sigmoidoscope (to see the part of the colon nearest the rectum, including the sigmoid [bendy] colon on the left side of the abdomen) or a colonoscope (to see the whole colon, including the part on the right side of the abdomen, performed under sedation), respectively.
Alternatively, a barium enema examination may be used to look at the whole colon. In this test, a liquid suspension of barium sulphate, which shows up on X-rays, is poured into the rectum through a narrow tube inserted through the anus. Usually a small balloon is then inflated in the rectum to pump in a small amount of air. This gives 'double contrast' to show the lining of the bowel in good detail.
For both procedures, the colon needs to be cleared by quite vigorous purgation (medicines are given to stimulate the intestines and clear out the bowel), which many patients find the most unpleasant aspect of the procedure.
There are advantages and disadvantages of each approach:
- Colonoscopy allows biopsy and therefore the presence of cancer can be confirmed under the microscope. But, even in skilled hands, the whole colon is seen in only about 90 per cent of procedures. Colonoscopy can be uncomfortable with a 1 in 5000 risk of death due to complications of perforation (puncturing) of the bowel.
- The barium enema is usually more comfortable, but it is performed without sedation. It nearly always shows up the whole colon, but in less detail than colonoscopy so very small polyps can be missed.
The need for screening is different for a person with strong family history of bowel cancer. In individuals who have a first-degree relative (e.g. a parent, brother, sister or child) who developed colorectal cancer before the age of 45, the life-time risk for colorectal cancer is 1 in 10.
What Causes Bowel Cancer?
About 90 per cent of the risk for bowel cancer is thought to be due to dietary factors, with the other 10 per cent due to genetic (inherited) factors, as shown by immigration studies of Japanese populations.
Dietary factors that increase bowel cancer risk are not yet clearly defined. Populations with a high-fibre intake tend to have a low risk of bowel cancer. However, the results of studies in which people, usually those who have already developed polyps, have been given high-fibre diets are disappointing.
The best available approaches for a low risk of developing bowel cancer are:
- A diet high in green vegetables, particularly cabbage, broccoli, brussel sprouts or cauliflower.
- A diet low in red meat. In particular, avoid burnt meat, which contains cancer-promoting chemicals called cyclic amines.
- Keeping to a normal body weight and taking regular exercise.
- Although still controversial, it seems that taking aspirin (e.g. Disprin) regularly (300mg per day or more i.e. one standard tablet) reduces the risk by about 50 per cent. However, prolonged use of aspirin carries a risk of intestinal ulceration and bleeding, so whether the benefits would outweigh the risks is unclear at present.
Approximately 10 per cent of bowel cancers have a strong genetic factor. The commonest is hereditary non-polyposis colon cancer (HNPCC or Lynch syndrome). This condition is caused by mutation in any one of at least five different genes. These genes carry the instructions for manufacturing proteins that can repair damaged DNA.
Inheritance of this type of cancer is autosomal dominant, which means that half the children of someone with HNPCC are at risk of inheriting the condition. When these genes are defective, DNA repair does not take place and damaged (mutant) DNA accumulates within cells, greatly increasing the cancer risk. The bowel cancers in affected individuals tend to develop as flat lesions rather than as polyps. The cancers more commonly affect the proximal (right sided) colon, whereas other cancers are more common in the distal colon (nearer the rectum) or rectum. They occur at a younger age and this condition should be suspected in anyone who develops bowel cancer before the age of 45.
About 1 per cent of bowel cancers occur in people who inherit a defect in the gene for familial polyposis coli. These people develop hundreds of adenomatous (pre-cancerous) polyps in the colon by the time they are in their teens and almost invariably develop bowel cancer by middle age unless the colon is removed.
Patients with ulcerative colitis or Crohn's disease of the colon (conditions that together affect about 1 in 800 of the population in Western countries) have about a five-fold increased risk of bowel cancer.
The risk is greater if the colitis (colon inflammation) seen in both conditions affects the whole colon, and if it has been present for more than ten years. The risk is probably reduced by regularly taking mesalazine (5-aminosalicylic acid), a medication that is widely used to reduce the risk of relapse in these diseases.