Lung Cancer Screening - Is it time to get a CT scan?

The United States Preventative Services Task Force (USPSTF) has come out with a preliminary recommendation in support of low dose chest CT scans to screen for lung cancer in certain high risk individuals. The recommendation can be viewed below. 
The recommendation does not cover all people who are or were smokers, only those who are considered high risk. For the purpose of this recommendation the definition of high risk includes all patients who meet the following criteria.

  • 20 pack years or more of smoking- Pack years are calculated by multiplying the number of packs smoked per day times the number of years of smoking. For example, someone who smoked 1pack per day for 30 years or 2 packs per day for 15 years would have 30 pack years of smoking.
  • Age 50-80
  • Current smoker or stopped smoking no more than 15 years ago

These criteria were developed after review of several studies and consideration of the benefits and harms of screening.

The benefits of screening obviously include the possibility of detecting lung cancer at an earlier more treatable stage. Although this would not prevent all lung cancer deaths, studies indicate significant reductions in mortality can be achieved with a properly designed screening program.

All screening tests have potential risks for the patients who undergo them. In the case of Chest CT's the risks include false positives resulting in further scans, anxiety, and invasive biopsies, as well as radiation exposure. One study estimates that if all former smokers in the 50-75 age range were to receive annual chest CT scans it would result in a 1.8% increase in the number of lung cancers per year or about 640 extra cases of lung cancer. The earlier a person begins screening the greater the cumulative lifetime radiation exposure and the greater the risk.

Additionally, the CT scan may detect some harmless cancers. Despite common perceptions, some cancers can remain in the body for life and never cause harm. We do not have a good method for separating these cancers from the harmful ones so screening may result in the detection and treatment of harmless cancers and some patients will suffer side effects from these treatments.

Another potential drawback to lung cancer screening is that some proportion of screened patients who are current smokers will incorrectly assume that a negative scan means they are cancer free and use this as a license to continue smoking. A negative scan does not rule out the possibility that cancer is present.  A small tumor may still contain millions of cancer cells yet be too small for the scan to detect. Smokers should be made aware that a negative scan has no diagnostic value at all and is NOT "a clean bill of health".

All of these factors were considered before making the current recommendation which was designed to best balance risk and benefit.  If you feel you may be a candidate for lung cancer screening discuss this with your doctor.

Michael Melgar

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