What is gastrointestinal cancer?

The gastrointestinal tract runs from the mouth to the anus, and includes the oesophagus (gullet), stomach, small bowel or intestine, and the large bowel (colon and rectum). Cancer can affect any part of the gastrointestinal tract, although, curiously, it is rare in the small intestine where most digestion takes place.

• Bowel cancer (colorectal) is the second commonest cause of cancer-related death (after lung cancer), affecting 6 per cent of the population in Westernised (industrialised) countries and causing death in about 3 per cent. About 25 per cent of all deaths are caused by cancer in industrialised countries, and bowel cancer accounts for 12.5 per cent of those deaths.
• Stomach cancer accounts for about 8 per cent of cancer deaths and occurs in twice as many men as women. It is gradually becoming less common but, sadly, this fall has been balanced by an increase in oesophageal cancer (particularly a glandular type called adenocarcinoma) in men.
• Oesophageal cancer accounts for about 3 per cent of cancer deaths and the ratio of affected men to women is 1.8:1.
• Cancer of the pancreas accounts for about 4 per cent of cancer deaths and affects both sexes approximately equally.
• Cancer that develops first in the liver (primary liver cancer) is strongly linked with hepatitis virus infection. It is uncommon in Western countries where the rate of hepatitis is relatively low, but is often the most common cause of cancer-related death in developing countries where hepatitis is much more frequent. Overall it accounts for only about 0.7 per cent of cancer deaths in Western countries. However, the liver is a common site for other gastrointestinal cancers to spread to, particularly colorectal cancer, resulting in so-called secondary deposits or metastatic cancer.

How do I reduce my risk of these cancers?

Several lifestyle changes can reduce your risk of getting gastrointestinal cancer.

Drink alcohol in moderation
A high alcohol intake is associated with an increased risk of cancers of the:

• oesophagus - particularly squamous cancer in which alcoholic spirits and smoking seem to have additive effects.
• pancreas - if high alcohol intake initially leads to chronic inflammation or pancreatitis, which carries an increased risk for pancreatic cancer.
• liver - if high alcohol intake leads to liver cirrhosis, the damage due to chronic inflammation which is a major risk factor for primary liver cancer.
• bowel.

Avoid smoking
Smoking doubles the risk for cancer of the pancreas and is, particularly when alcoholic spirits are also drunk, associated with increased risk for cancer of the oesophagus.

Eat plenty of green vegetables
A high intake of green vegetables is associated with a reduced risk for bowel cancer and a high vitamin C intake (found in fruits and green vegetables) is associated with reduced risk for stomach cancer.

Avoid preserved or burnt meats
Salted and smoked meats are associated with a high risk of stomach cancer, probably due to their high content of nitrates which in the stomach form highly carcinogenic nitroso-amines.

Burnt meats have been found to be linked with bowel cancer because of their high content of carcinogenic cyclic amines. A high intake of red meats is particularly associated with increased risk of bowel cancer.

Keep to a normal weight
Obesity carries an increased risk of bowel cancer. Obesity also increases the risk of diabetes which itself is linked with a modestly increased risk of pancreatic cancer.

Take regular exercise
Regular physical activity is linked with a reduced risk for bowel cancer, regardless of body weight.

Can screening tests detect gastrointestinal cancers before they cause symptoms?

Screening is the process of checking people who have no symptoms for unsuspected disease, which can then be treated more successfully than if the disease had been left until it showed itself.

Screening programmes are already in place for breast cancer and cervical cancer in women. Screening has been proposed for gastrointestinal cancers. Each cancer needs to be considered separately but any screening programme should have certain common properties that are essential for success:

• the disease should be fairly common in the population or group of people that is considered to need screening (otherwise the benefit to any one individual will not be sufficient to counterbalance the risk and inconvenience of screening to the rest).
• a diagnostic test to detect the condition is needed that is simple, cheap and reliable.
• effective treatment should exist.

The last of these properties might seem straightforward – surely surgery is effective treatment for all gastrointestinal cancers if they are caught early?

Although this is a reasonable generalisation this statement is not true in all cases. Many cancers shed small numbers of cells or 'micrometastases' into the blood or lymph ducts from a very early stage so removal of the original (primary) cancer may not cure the patient. In these cases, the body's own immune response to these tumour cells seems at least as important as the speed with which the primary cancer is identified and removed.