NLST: yearly low-dose CT scans cut lung cancer deaths in heavy smokers
Three annual low-dose CT scans reduced lung cancer deaths by a fifth compared with chest X-rays in current and former heavy smokers.
The National Lung Screening Trial randomised 53,454 current or former smokers aged 55-74 with at least 30 pack-years to three annual screens with low-dose helical CT or chest radiography at 33 US centres.
The primary endpoint was lung cancer mortality. After a median 6.5 years of follow-up there were 247 lung cancer deaths per 100,000 person-years in the CT arm and 309 in the radiography arm, a 20% relative reduction; all-cause mortality also fell by 6.7%. The trial was stopped early for benefit.
NLST is the evidence base for US Preventive Services Task Force lung screening recommendations and for national programmes that followed.
- Lung cancer mortality reduced by 20.0% (95% CI 6.8-26.7) with low-dose CT versus chest radiography
- All-cause mortality reduced by 6.7% (95% CI 1.2-13.6)
- 24.2% of CT screens were positive, and 96.4% of positive screens were false positives
- Roughly 320 people had to be screened to prevent one lung cancer death over the trial period
For people with a heavy smoking history, an annual low-dose CT scan is one of the few screening tests proven to reduce cancer deaths. Most abnormal scans are not cancer, so screening must be paired with careful nodule management. It does not apply to never-smokers or light smokers.
- High false-positive rate with the 4 mm nodule threshold used in 2002-2004; modern Lung-RADS criteria reduce this
- Comparator was chest X-ray, itself of no proven benefit, so the effect versus no screening may differ
- Participants were younger, better educated and more often former smokers than the US smoking population
- Uptake of screening among eligible people remains low in most countries
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