In Western society about one person in 25 will develop cancer of the lower (large) bowel, which makes it one of the most common cancers. About half of those affected may be cured with an operation. Others with more advanced cancer may require additional treatment — usually with chemotherapy, sometimes with radiotherapy.

As with most cancers, early detection greatly improves the chances of cure. Unfortunately, the early symptoms of bowel cancer often seem trivial and are therefore ignored.

Altered bowel habit is perhaps the most important sign. Most people are aware of their usual bowel habit. For many this will mean they open their bowels once a day, for others it might be twice a day and for some it may be only 2 or 3 times a week. All of these patterns can be perfectly normal. It is when there is a change to this predictable pattern that attention is needed.

There is no 'typical' change to be concerned about. Bowel actions might become more frequent or less frequent. They may seem looser (runny) or harder. The important thing is that they are different. Any change that continues for more than a day or 2, and can't be explained by a significant change in diet, should be reported to a doctor.

Another vitally important sign that should never be ignored is bleeding. If there is blood mixed with the bowel motions or noticed on the toilet paper, further investigation is needed.

Testing for bowel cancer
The usual investigation performed when problems with the large bowel are suspected is a test known as a colonoscopy. A long snake-like tube (colonoscope) containing a fibre-optic viewing system is passed through the anus. The doctor performing the test is able to see the inside surface of the bowel and take samples of any suspicious areas for further testing. The colonoscope is gently manoeuvred along the whole length of the large bowel, allowing a thorough examination.

There is little, if any, discomfort in having this test. Apprehensive people may need light sedation but most people find the test easy to tolerate and some enjoy seeing their insides on the television screen that usually records the procedure.

Who is at risk of bowel cancer?
Most at risk of bowel cancer are those with a close relative with the disease, those with polyps (small growths that are usually harmless) of the bowel, and those with chronic inflammatory bowel diseases such as ulcerative colitis or Crohn's disease. It is recommended that those with a high risk of cancer have regular checks so that if it does develop, cancer can be detected early and then treated.

What causes bowel cancer?
We don't really know what causes bowel cancer, although diet is one of the main suspects. Most bowel cancers start as harmless growths (polyps) that turn into tumours. Just why a polyp starts to grow, or why one becomes cancerous, isn't known.

What we do know is that people who've had diseases that inflame the bowel for a long time are more likely to get bowel cancer than other people. So are people who've had close family members (such as parents, brothers or sisters) with bowel cancer, especially if they got it while aged under 50.

And, like most cancers, it's much more common in people over 50 than in younger people. You can't catch it from someone else, or pass it on to someone else if you have it.

How can I avoid bowel cancer?
What a person eats is probably important. Certainly, fewer people get it in countries where they eat lots of fruit, vegetables and cereal foods, and not much meat and animal fat. It's because of these clues and other research that most scientists think this sort of diet is good for you and diets rich in fruit and vegetables, and low in fat, could help to reduce your chance of developing bowel cancer.

Eating 2 pieces of fruit and 5 serves of vegetables a day could reduce your overall risk of cancer. This is part of a healthy diet for preventing heart disease too.

People who don't get much exercise also have a higher risk of bowel cancer. So keep active. That's something else that's good for your health in all sorts of ways.

What are the warning signs?
If you're over 50, or there has been bowel cancer in your family, it's a good idea to talk to your GP about getting checked, even if you don't have symptoms. Remember, the earlier bowel cancer is diagnosed, the better the chances that treatment will be successful.

You can't help getting older, and you can't help it if other people in your family had bowel cancer. But there are other things you can do.

The most common signs of bowel cancer are a change in how often you go to the toilet (doctors call this 'bowel habits') that doesn't return to normal after a couple of weeks. Faeces may be looser than usual, like diarrhoea, and you may find yourself going to the toilet more often. You may also be constipated or find that you feel you haven't finished after going to the toilet, or that you feel like going, but nothing happens.

Bleeding from the anus (rectal bleeding)
Blood in the faeces is usually caused by piles (haemorrhoids). Piles are unpleasant and should be treated, but they aren't dangerous. They usually have other symptoms as well as bleeding. They can be sore or itchy, and there are often little lumps around the rim of the anus that you can feel. But even if you have symptoms of piles, you should see a doctor if there's blood in your faeces.

Sometimes your doctor may actually be able to feel a growth in your abdomen. And there can be pain in the abdomen, particularly in older people. These symptoms can be caused by all sorts of things (rectal bleeding is quite common, and changes such as diarrhoea or constipation even more so) and in most cases it won't be cancer.

But if you have symptoms like these, see your doctor.

There is also a test you can buy at the chemist and do yourself at home to check for blood in your faeces (you can't usually see a small amount of dark blood). It's called the Faecal Occult Blood Test (FOBT), and it's much simpler than its name (occult just means 'hidden'). With the test you put a bit of 3 different bowel motions on slides or cards that you take to your doctor or back to the chemist to be sent away for analysis. With some kits, you do the testing yourself at home.

There are several types of FOBT. Some won't work properly unless you avoid certain foods for several days beforehand. Follow the instructions that come with whichever FOBT you buy.

The test finds even tiny amounts of blood in your faeces. Blood in the faeces could have come from a cancer in the bowel. It doesn't mean you do have bowel cancer. Most people who have blood in their faeces have it for some other reason. But in a few cases it will be cancer.

FOBT won't catch every bowel cancer. But by doing it regularly, you increase your chances of picking it up early. There's a 90 per cent chance that bowel cancer can be cured if it's found early enough. So if you have a positive result, talk it over with your doctor.

If you're over 50, it's a good idea to do a FOBT at least every 2 years. Every year is even better. If you have a family history of bowel cancer you could be at higher risk, even if you're under 50. Talk to your doctor about it. They may want to do a colonoscopy every 5 years, to look very carefully for early bowel cancers.