Evidence Trace, complete trial record

In plain terms

In plain terms: Low-dose CT screening for lung cancer in heavy smokers has strong evidence from human clinical trials. The benefit shown in those trials is if that describes your situation.

Low-dose CT screening for lung cancer in heavy smokers

A Replicated: replicated trials on a qualifying endpoint

Category Devices

Evidence Large randomized trials of low-dose CT screening against chest X-ray or no screening

Reviewed October 2026

PMIDs 21714641 · 31995683 · 37639247

The endpoint this grade is based on: Hard clinical endpoint (mortality, major event)

The evidence as the record states it

Evidence record

PMID 21714641 PMID 31995683 PMID 37639247

NLST (National Lung Screening Trial Research Team, N Engl J Med, 2011; PMID 21714641): 53,454 heavy smokers at 33 US centers, three annual low-dose CT scans against chest X-ray; lung cancer deaths 247 against 309 per 100,000 person-years, 20.0% lower (6.8 to 26.7); death from any cause 6.7% lower (1.2 to 13.6); 24.2% of CT screens were positive and 96.4% of positive results were false; lung cancer incidence 13% higher with CT. Funded by the US National Cancer Institute. NELSON (de Koning et al., N Engl J Med, 2020; PMID 31995683): 13,195 men and 2,594 women aged 50 to 74 who smoked or had smoked, in the Netherlands and Belgium, volume CT at baseline and years 1, 3 and 5.5 against no screening; at 10 years lung cancer deaths 2.50 against 3.30 per 1,000 person-years in men (rate ratio 0.76, 0.61 to 0.94), 0.67 (0.38 to 1.14) in women; 2.1% referred for suspicious nodules. Bretthauer et al. (JAMA Intern Med, 2023; PMID 37639247): lifetime gained 107 days (-286 to 430), not significant.

PMID 21714641 PMID 31995683 PMID 37639247

Evidence by specific use

Lung cancer deaths, current and former heavy smokers aged 50 to 74

Grade A

NLST (N Engl J Med, 2011; PMID 21714641): lung cancer deaths 20.0% lower with low-dose CT than with chest X-ray, 62 fewer per 100,000 person-years. NELSON (de Koning et al., N Engl J Med, 2020; PMID 31995683): lung cancer deaths 24% lower in men at 10 years (rate ratio 0.76, 0.61 to 0.94). Two independent trials, a hard outcome: A.

PMID 21714641 PMID 31995683

Death from any cause, current and former heavy smokers

Grade C

NLST found deaths from any cause 6.7% lower with CT than with chest X-ray (PMID 21714641). A pooled analysis of screening trials estimated 107 days of lifetime gained, not significant (Bretthauer et al., 2023; PMID 37639247). One significant trial, not repeated: C.

PMID 21714641 PMID 37639247

Why Grade A and not higher

Grade A requires a hard clinical endpoint or objectively measured functional outcome, independently replicated across at least two trials. Low-dose CT screening for lung cancer in heavy smokers meets that standard based on the trials cited above. A downgrade to Grade B would follow if replication attempts produced null results, if the effect size proved substantially smaller in a broader population, or if the studied dose proved impractical to sustain.

What this grade covers and what it does not

Grade A on lung cancer deaths in current and former heavy smokers: two independent large trials found them lower, by 20% against chest X-ray in the US (NLST; PMID 21714641) and by 24% against no screening in men in the Netherlands and Belgium, in the NELSON trial (PMID 31995683). A hard outcome replicated across groups: A. Grade C on death from any cause: NLST found it 6.7% lower against chest X-ray, and a pooled lifetime analysis was not significant (PMID 37639247). WHAT THIS GRADE DOES NOT COVER: people who never smoked or smoked less than the trials required; chest X-ray screening; and women, where NELSON's result was not significant on its own.

What would move this grade

A null result in a well-powered independent replication trial, or evidence that the effect does not hold at a practically sustainable dose, would prompt downgrade to Grade B.

How to track whether this is working Measured in the trials: deaths from lung cancer and from any cause in national registries, positive and false-positive screens, and lung cancer diagnoses.