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When lung cancer has spread, it's very difficult to treat successfully. Yet the symptoms, such as persistent cough, are often noticed only later on in the disease.

For about three-quarters of people with lung cancer, their disease is advanced by the time they are diagnosed.¹ This is why there has been so much interest in screening for lung cancer. This is where doctors try to pick up the disease early, before symptoms appear. It's done by testing large numbers of apparently healthy people, to find out who has the disease.

Several studies have been done to see if screening can detect lung cancer earlier and improve people's chances of surviving the disease. The studies have used different methods of testing, such as X-rays of your chest, or tests on the fluid (also called phlegm or sputum) that you cough up. More recently, a new way of screening called a CT scan has been used to screen people who smoke and others who have a high chance of getting lung cancer. CT scans use a special type of X-ray that produces pictures of "slices" (cross sections) of your body.

Most studies have found that screening doesn't work, and some studies have found that screening could be harmful. Having chest X-rays twice a year may do more harm than good. People with lung cancer who have frequent X-rays are more likely to die from the disease than people who are not screened.²

An annual X-ray combined with a sputum test every four months does have benefits. A sputum test is when a sample of phlegm you cough up is looked at under a microscope. Studies have shown that³:

• People with lung cancer who had this combination of tests were more likely to be diagnosed earlier, and more were treated successfully.
• Most importantly, people who had this screening lived for an average of five years longer than people who were not screened.
• But the number of advanced cancers diagnosed didn't reduce, nor did the screening reduce the total number of deaths from the disease.
• Overall, screening didn't help doctors diagnose lung cancer earlier and save lives.

More recent studies of screening have shown that low-dose CT scans are better than X-rays at finding early signs of lung cancer. This means that more cancers are treated successfully.³ But CT scans didn't seem to reduce the number of advanced lung cancers diagnosed.

Researchers are also worried that finding lung cancer when it is small may not necessarily help people to live longer.³ Small, fast-growing (aggressive) tumors may be just as dangerous as larger ones. Research suggests that lung cancer may start to spread very early. This means that current tests cannot detect them soon enough to make screening worthwhile.³

Until research shows that screening can reduce the number of people who die from lung cancer, specialists don't recommend that screening programs be set up.^{2 3}

Researchers are trying to develop a blood test that could check for early lung cancer.⁴ But the research is at a fairly early stage, and these tests are still experimental. At the moment, doctors can't use blood tests to screen for lung cancer.

This information is for educational use only, and is not a substitute for prompt professional medical advice. Readers should always consult a physician or other professional for advice and treatment. ©BMJ Publishing Group Limited 2008. All rights reserved.