Screening for cancer means testing people who appear to be well, and have no symptoms, in order to find tumours at a very early stage. If a cancer is detected early it is usually (but not always) more treatable, and more likely to be cured, than if it is found later. So a successful screening programme should improve the life expectancy of people with that particular cancer.

There are hundreds of different types of cancer - some are very common, some are less common and many are quite rare. At the moment there is no way of screening to see if someone simply 'has a cancer' but there are screening tests for certain specific types of cancer such as breast cancer and cancer of the cervix.

For screening to be useful for any particular type of cancer then there must be:

• reliable tests to find that cancer before any symptoms occur within the body
• evidence that finding and treating that type of cancer at an early stage will improve the chances of a cure.

For many kinds of cancer no effective or reliable screening tool has been discovered, despite a great deal of research.

The only test that could reliably discover early cancers of the oesophagus would be an endoscopy and biopsy. This involves passing an endoscope, which is like a thin flexible telescope, through the mouth and throat into the oesophagus. Photographs of the oesophagus can then be taken and small samples of cells (biopsies) taken from any abnormal looking areas, for examination under the microscope. This test involves a stay of several hours in hospital, often with some sedation and although it is not painful it can be quite uncomfortable. Unfortunately it simply is not practical to do this examination on a regular basis on the whole population as a screening test for cancer of the oesophagus.

Endoscopies can be used, however, for people who are at greater risk of developing cancer of the oesophagus.

One condition that is associated with a particular type of oesophageal cancer, called an adenocarcinoma, is Barrett's oesophagus. This is usually a benign (non-cancerous) condition but people who have it are as up to 40 times more likely to develop adenocarcinoma of the oesophagus than someone who does not have the condition. For this reason people who are found to have Barrett's oesophagus are often offered endoscopies at intervals of 6 to 24 months (depending on how severe their condition is) to check that a cancer has not developed.