Bowel cancer

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 colon is not the only organ affected. The syndrome also carries an increased risk of cancers of the stomach, ovaries, breasts and uterus.

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.

What are the symptoms of bowel cancer?

. Because early cancers often cause no symptoms, screening of symptom-free individuals 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. Cure is nevertheless still possible. The earliest symptom is often bleeding from the back passage. Later changes include 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 (ie 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. This obstruction is a surgical emergency requiring immediate admission to hospital, since the bowel is at risk of becoming gangrenous if the obstruction is not relieved.

In the proximal colon, the lumen (the space inside) is larger (about 4 or 5cm in diameter) and less likely to become obstructed.

Cancers of the rectum typically cause rectal bleeding, which can easily be mistaken for bleeding haemorrhoids (piles). Other symptoms include the feeling that you haven't fully emptied your bowel accompanied by a need to frequently empty the bowel. Loss of appetite and weight loss tend to be late features in bowel cancer.

How is bowel cancer diagnosed?

. The doctor might feel a cancer of the rectum 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, the doctor will use 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).

Colonoscopy is usually performed using intravenous sedation and takes about 30 minutes. Flexible sigmoidoscopy takes about 10 minutes and can usually be done without sedation.

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. The procedure takes about 30 minutes.

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, but it is usually performed with sedation, which has the added advantage that the individual usually cannot remember the procedure. Complications include a slight risk of perforation (puncturing) of the bowel and a very slight risk of death (about 1 per 5000).
- 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.

Scanning techniques (CT scanning or ultrasound) are increasingly being studied as possible ways to diagnose bowel cancer, but they are not yet reliable enough for routine use.

Screening is now recommended in the USA for all individuals over the age of 50. It is done by a combination of an annual test for non-visible (occult) blood in the faeces (faecal occult blood test), plus some form of endoscopy, either flexible sigmoidoscopy or colonoscopy, every three to five years. Experts have not yet firmly established whether this approach can prolong life, and screening has not yet been introduced routinely in the UK.

A positive faecal occult blood test is linked with approximately a 10 per cent chance of cancer or a 34 per cent chance of a polyp. However, the test is negative with up to 50 per cent of cancers (this figure falls to about 30 per cent when the test is done on three consecutive days). Therefore, this test is not sufficiently reliable for routine diagnosis of symptom free patients.

The need for screening is different if you have a strong family history of bowel cancer. In individuals who have a first-degree relative (eg 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.

The consensus of opinion is that such individuals should be offered screening, probably by full colonoscopy, every five years, starting 5 to 10 years younger than the age at which the relative was diagnosed. Individuals who have two first-degree relatives with colorectal cancer have a one in six life-time risk and should be similarly offered screening.

What other conditions might cause similar symptoms?

. This depends on the symptoms.

Rectal bleeding

- It is extremely common to notice a few spots of blood on the toilet paper after passing stools. If there is no blood in the toilet bowl, this is most likely to be due to minor damage to a blood vessel in the skin of the anus. If it persists, the problem requires investigation to exclude significant disease of the anus.
- Blood in the toilet bowl that is separate from the faeces and is bright red is commonly due to bleeding from haemorrhoids (piles). However, this sort of bleeding cannot be distinguished from bleeding due to a rectal cancer without further investigation.
- Blood that is mixed in with the stool is more likely to have a worrying cause but benign (non-cancerous) possibilities include bleeding from diverticular disease or from colitis.

Diarrhoea or other change in bowel habit

Diarrhoea that has only been present for a few days, or even up to three weeks, is most commonly due to infection ie gastroenteritis. Diarrhoea that carries on for longer than three weeks is rarely due to infection and requires urgent investigation.

Benign causes include:

- colitis, an inflammation of the colon (eg ulcerative colitis or Crohn's colitis).

- diverticulitis, an inflammation of the little pea-sized pouches that can develop in the wall of the bowel, in which case the diarrhoea may be bloody.
- lactose intolerance.
- irritable bowel syndrome , in which case the diarrhoea is watery and not bloody. Irritable bowel syndrome mimics some of the symptoms of bowel cancer including colicky abdominal pain and diarrhoea. However, the diarrhoea is always non-bloody, the symptoms are intermittent and IBS typically starts in the adolescent or young adult at an age when bowel cancer is very rare.

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