Clinical Question

Does low-dose computed tomography (CT) screening for lung cancer reduce lung cancer–related mortality and what are the harms?

Evidence-Based Answer

Low-dose CT screening decreases deaths from lung cancer in people 40 years and older with an absolute risk reduction of approximately 0.4% and a number needed to screen of approximately 226 people over an average of 8.8 years of follow-up to prevent one death. Low-dose CT screening is associated with harms, including overdiagnosis and false-positive results, with a number needed to screen to produce one harmful outcome of approximately 44.¹ (Strength of Recommendation: A, systematic review of randomized controlled trials.)

Practice Pointers

Lung cancer is the leading cause of cancer-related death in the world, with an estimated 139,600 lung cancer deaths in the United States in 2019.^2,3 Tobacco smoking is the most significant risk factor for developing lung cancer. Low-dose CT screening is an established tool used to detect lung cancer at an early stage.⁴ The authors of the Cochrane review sought to determine if low-dose CT screening reduces lung cancer–related mortality and the possible harms associated with screening.¹

The Cochrane review included 11 randomized controlled trials. Eight trials with 91,122 participants assessed lung cancer–related mortality, and three trials with 60,003 participants assessed possible harms of screening.¹ The mortality follow-up duration ranged from five to 12 years. The studies included adults 40 years and older from the United States and Europe who were asymptomatic and had not been diagnosed with lung cancer. All trials used low-dose chest CT as the primary test, and the frequency and duration of low-dose CT varied between trials; annual low-dose CT screening occurred in nine trials. Patients included in the trials generally had a strong tobacco smoking history, although the specific amounts varied, and most trials had an entry requirement of a 20-pack-year smoking history or more.

Compared with those who received no screening or were screened with chest radiography, patients who had annual or biennial low-dose CT screening for lung cancer had a relative risk reduction of 21% in lung cancer–related mortality (relative risk = 0.79; 95% CI, 0.72 to 0.87; number needed to screen is approximately 226 over an average 8.8 years of follow-up).

The review sought to identify harms from low-dose CT screening, including overdiagnosis, false-positive results, and health-related quality of life, such as anxiety and fear, arising from testing. After baseline screening, more invasive testing was performed in the low-dose CT screening group, including surgical diagnostic procedures. For every 10,000 people screened with low-dose CT, 363 unnecessary invasive tests were performed, yielding an approximate number needed to harm of 44 over an average 8.8 years of follow-up.

Five trials in the review estimated overdiagnosis via screening, which was defined as the detection and diagnosis of lung cancer that would not have caused symptoms or death if it had been left untreated. Overdiagnosis was calculated by estimating the risk of lung cancer in the screened group compared with the control group following the active phase of screening. The results suggested an increased rate of overdiagnosis, although it was not statistically significant.

In 2021, the U.S. Preventive Services Task Force updated their lung cancer screening recommendation (grade B recommendation) to include annual low-dose CT screening for adults 50 to 80 years of age who have a 20-pack-year smoking history and currently smoke or have quit in the past 15 years.⁵ The Cochrane review supports these recommendations for people 40 years and older and for those who have a smoking history of 20-pack-years. The U.S. Preventive Services Task Force chose to recommend screening starting at 50 years of age for a better balance of benefits and screening-related harms. Family physicians should be able to discuss the risks and benefits with patients who may be appropriate for this evaluation.

The practice recommendations in this activity are available at https://www.cochrane.org/CD013829.