Lung CT scan for cancer: Should you be screened?

David Midthun, M.D.

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If you're a smoker or former smoker, you may worry about your risk of getting lung cancer or dying from it. A major study of heavy smokers, called the National Lung Screening Trial (NLST), compared lung CT scans and chest X-rays and found that getting a lung CT scan lowered the risk of dying of lung cancer. This is the first study to show lung cancer screening may save lives. However, not all study details have been released for careful review by doctors and scientists other than those who conducted the study. For that reason, medical groups, including the American Cancer Society, don't yet recommend lung cancer screening to smokers and former smokers.

David Midthun, M.D., is a consultant in the Division of Pulmonary and Critical Care Medicine at Mayo Clinic, Rochester, Minn. He explains the results of the NLST study and the pros and cons of using lung CT scans for lung cancer screening.

Results of the National Lung Screening Trial suggest that smokers and former smokers might benefit from lung CT scan screening. Is that the case?

The result of the NLST is the first indication that any test can reduce deaths from lung cancer. The study involved more than 50,000 current and former heavy smokers — people who smoked the equivalent of a pack of cigarettes a day for 30 years — ages 55 to 74. Participants were randomized between low-dose spiral CT scan and chest X-ray at the start of the trial. They received annual screening tests for three years and then were followed for five years. The initial results of this trial revealed a reduction in lung cancer deaths with CT scan screening. The results showed 354 lung cancer deaths had occurred among those who had been screened with CT scan vs. 442 deaths among those who were screened with chest X-ray. That represents a 20.3 percent reduction with CT screening.

With some cancers, doctors encourage people to get regular screening. Will lung cancer be added to that list?

Currently, in most cases, screening for lung cancer is not recommended and not covered by Medicare or most insurance companies.

Screening for breast, cervical and colon cancers has been shown to reduce your risk of dying of these diseases when compared with those who don't get screened. Doctors recommend screening for these cancers because doing so has proved beneficial for a group of people in the study setting. It remains to be seen whether the NLST results regarding lung cancer will lead to changes in screening guidelines by groups such as the American Cancer Society or U.S. Preventive Services Task Force.

Will lung CT scans help doctors diagnose lung cancer earlier?

Prior lung CT scan studies have shown that screening increases detection of early-stage cancer, and the NLST results provide evidence that those diagnoses end up being more beneficial than harmful in that they reduce the likelihood of death.

Being diagnosed with lung cancer at an earlier stage does make it more likely that surgery — the best treatment for most types of lung cancer — can remove and cure the cancer.

What are the risks of lung CT scans?

Risks of lung CT scans can include:

• Finding abnormalities that are eventually determined to not be cancer. CT scans find abnormalities in about 20 to 60 percent of smokers and former smokers, but most of these abnormalities are scars from inflammation or other noncancerous conditions. The CT scan's sensitivity can result in doctors suspecting the possibility of cancer where there really is no cancer, which results in invasive follow-up tests, unnecessary surgery, and anxiety for those getting screened and their loved ones. In other words, screening leads to necessary invasive tests and surgery for lung cancer, but these tests end up being unnecessary if it's eventually determined that the spot first found on a CT scan isn't lung cancer but instead something benign.
• Finding very small abnormalities that require follow-up scans. CT scans are so good at seeing nodules or spots on the lung that they can see very small nodules that don't need immediate testing, but do need follow-up CT scanning to detect any changes.
• Exposure to radiation. CT scans expose you to a small dose of radiation. Compared with some other parts of the body, such as the breast, lungs have greater potential for developing radiation-induced cancer. Several studies have estimated an increased risk of developing cancer from CT scan radiation. The risk of developing cancers from CT scans is small, but it's a reminder of the importance of weighing the risk vs. the benefit of any medical test.

What will you tell patients who ask about lung CT scans?

Currently, no major medical organizations recommend screening for lung cancer. However, with the results of the NLST, that appears likely to change. There is much to be learned about who may benefit from lung CT scan screening and who may not benefit. Until then, it's best to discuss the potential benefits and risks of lung CT scan screening with your doctor. Despite the news about the potential benefits of lung CT scan screening, it's still important to remain focused on risk reduction in trying to keep people from starting smoking and getting smokers to stop smoking.

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