Study: Lung CT Best for Highest-Risk Group

July 18, 2013

News Review From Harvard Medical School -- Study: Lung CT Best for Highest-Risk Group

Low-dose CT scans could be most useful as a lung-cancer screening test if given only to those with the very highest risk, a new study suggests. The study suggests a way to further refine criteria for who should get the scans. Chest CT finds many lung cancers but also causes many false alarms. Researchers took a closer look at results from the National Lung Cancer Screening Trial. That study reported results in 2011. It found that chest CT screening of a high-risk group could reduce lung cancer deaths 20%. Scans were given to heavy smokers, ages 55 through 74 years. The study also included former heavy smokers who had quit no more than 15 years earlier. The new study further divided people into risk groups based on how much they smoked, family history of lung cancer and other factors. CT screening prevented 60 times as many lung-cancer deaths among the highest-risk group as among the lowest-risk group. For each death prevented, there were 65 false-positive results for those at highest risk and 1,648 for those at lowest risk.  The New England Journal of Medicine published the study. HealthDay News and MedPage Today wrote about it July 17.

By Howard LeWine, M.D.

Harvard Medical School

What Is the Doctor's Reaction?

A good screening test can detect a problem safely, accurately and while there's time to do something about it. 

Colonoscopy is a good example.  It can detect colon cancer at an early, curable stage.  Better yet, it can find polyps that can be removed before they turn into cancer.

Although lung cancer is a leading cause of cancer death, we have no effective screening test for it.  Chest X-rays don't detect tumors at an early stage.  Chest CT scans are better at detecting early lung cancers.  In fact, past research of older smokers has shown that screening CT scans could lower lung-cancer deaths by 20%. 

But CT scans have an unacceptably high rate of false-positive ("false alarm") results.  These are abnormal CT scan results that require further tests and, in many cases, surgery even though no cancer is present.

A new study explores the value of chest CT scanning that is performed only on those with the highest risk of lung cancer. The study analyzed information about more than 26,000 people in the National Lung Screening Trial. It was sponsored by the National Institutes of Health. The New England Journal of Medicine published results this week.

The study examined the usefulness of screening CT scans based on people's risk factors for lung cancer.  These factors include how long people have smoked, family history of lung cancer and exposure to asbestos on the job. 

The results were striking:

• The number of lung-cancer deaths prevented was 60 times higher in the group with the highest risk of lung cancer compared with those at lowest risk.
• False-positive results were much lower in those who had a high risk of lung cancer compared with the lowest-risk group. For each lung-cancer death prevented, there were 65 false-positives in the high-risk group and 1,648 in the lowest-risk group.
• Only 1% of the lung-cancer deaths prevented by screening were among those in the lowest-risk group.

These results suggest that CT scanning as a screen for lung cancer might work best if reserved for those at the very highest risk.

What Changes Can I Make Now?

Smoking is the most important risk factor for lung cancer that you can change.  So the biggest change you can make now to reduce your risk is to avoid smoking.  If you have trouble quitting on your own, talk to your doctor about a smoking cessation program.

Smoking is not the only risk factor you can change.  These steps also may lower your risk of developing lung cancer:

• Avoid secondhand smoke.
• Avoid exposure to radon.  Install radon detectors in your home.  If levels are high, hire professionals to address the problem.
• Reduce your exposure to asbestos.  Have a certified home inspector determine whether your home contains asbestos.  If found, it can be removed, covered or sealed. Work-related exposure to asbestos can be reduced by following standard safety procedures. 
• Eat more fruit and vegetables.  Studies suggest that people who rarely eat fruit and vegetables have higher rates of lung cancer than those who eat them regularly.  Green tea, red wine and soy foods have also been linked to a reduced risk of lung cancer. 

If you have a family history of lung cancer, the measures above are even more important.

Some experts and groups recommend CT scans as a screening test for lung cancer and some do not.   For example, the American Lung Association suggests using the same criteria as the National Lung Screening Trial. This means that low-dose (low-radiation) CT scans are recommended for people who:

• Are 55 to 74 years old
• Smoke now or in the past
• Have a smoking history of 30 pack-years or more (for example, 1 pack per day for 30 years, ½ pack a day for 15 years, etc.)
• Do not have a history of lung cancer

But, the U.S. Preventive Services Task Force does not currently recommend CT scanning as a screening test.  This is an influential group that independently reviews evidence related to preventive care. Of course, the task force's advice could change.

If you have factors that increase your risk of lung cancer, talk to your doctor about this new study. Ask whether you should have a screening CT scan.

What Can I Expect Looking to the Future?

In the future, research should address several questions about how best to prevent lung cancer. They include:

• How can smokers reliably quit and avoid relapse?
• What is the role of diet?
• What screening test or combination of tests is best?
• Who should be screened?
• Can genes be used to screen those at high risk for lung cancer?  These may be particularly important for lung cancer among nonsmokers.

In the future, you can expect to see fewer cases of lung cancer and related deaths because fewer people are smoking.   I hope that this trend will continue.  Legislative measures, such as cigarette taxes and bans on public smoking, may discourage smoking even more over time.