Suitable Screening Intervals for Low-Dose CT Lung Cancer

In the United States, lung cancer screening is currently offered during routine clinical care. The US Preventive Services Task Force (USPSTF) recommends that high-risk individuals go for annual low dose chest CT (LDCT) screening based on results from the National Lung Screening Trial (NLST). High-risk individuals include those between the ages of 55 and 80, have a history of smoking at least 30 packs a year and currently smoke or stopped within the past 15 years.

The NLST showed a 20 percent reduction in lung cancer mortality in the intervention group as compared to the control group. The control group received three annual chest radiographs while the intervention group received three annual LDCTs. This is what prompted the USPSTF recommendation. It, however, raises some issues including:

  • The decision was not based on biological reasons and it raises concerns as to whether annual screening is necessary or appropriate for those that already qualify for lung cancer screening. 

  • Based on lung cancer screening studies, a longer time between screening intervals may lead to late detection of cancerous tumors for high-risk patients. On the other hand, doing fewer LDCTs on patients whose disease is benign may have minimal damage as compared to over-diagnosis and unnecessary interventions.
     
  • Selecting patients using a risk-prediction tool that includes other risk factors such as a family history of lung cancer or being diagnosed with chronic obstructive pulmonary disease (COPD) will improve selection of those at the highest risk of lung cancer.

Based on a later analysis of NLST, patients that show a low probability of developing lung cancer within two years on their initial baseline screening may benefit from follow-up. This should be after a prolonged screening interval of between one and two years.

If their risk profile changes based on the appearance of a new pulmonary nodule or whichever other relevant factor, it then becomes appropriate to change to annual LDCT screening.

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