Low-dose CT screening is shown to reduce lung-cancer deaths

Historical milestone — this page describes an event dated 2011. It is not current breaking news.

Why nobody screened for lung cancer before this

Lung cancer kills more Americans than any other cancer, and for decades there was no screening test worth offering.

Chest x-rays had been tried. They found tumors, but they did not lower the death rate, because by the time a tumor shows on a plain film it is often past the point where finding it changes anything.

Then low-dose computed tomography arrived. A CT scanner takes x-ray images from many angles and builds a cross-section, and a low-dose protocol does it with a fraction of the radiation of a standard chest CT. Early studies showed it picked up small tumors. The open question was whether picking them up earlier meant fewer people dying.

The trial

The National Lung Screening Trial, funded by the National Cancer Institute, enrolled 53,454 people at high risk of lung cancer at 33 US medical centers between August 2002 and April 2004.

Participants were randomized to three annual screens with either low-dose CT, at 26,722 people, or a single-view chest x-ray, at 26,732. Cases and deaths were tracked through the end of 2009. Adherence to screening was over 90%.

What it found

Deaths from lung cancer ran at 247 per 100,000 person-years in the CT group and 309 per 100,000 person-years in the x-ray group. That is a relative reduction in lung cancer deaths of 20.0%, with a confidence interval of 6.8% to 26.7%.

Death from any cause was also lower in the CT group, by 6.7%. That second number matters, because a screening test can shift deaths between categories without helping anyone. Here it did not.

The results were published in the New England Journal of Medicine in 2011, and they changed practice worldwide.

The part the headlines skipped

The same paper reported the cost of that 20%.

Over the three rounds, 24.2% of low-dose CT screens were positive, compared with 6.9% of x-rays. And 96.4% of those positive CT results were false positives.

Read that again. For every hundred people told their scan showed something, more than ninety-six had nothing. Each of them faced repeat scans, sometimes a biopsy, and weeks of fear.

Lung cancer incidence was also higher in the CT group, 645 per 100,000 person-years against 572. Some of that gap is overdiagnosis: cancers found that would never have caused harm in that person's lifetime, but which get treated anyway. Our page on benefits and harms of screening covers how these trade-offs are weighed.

None of this cancels the 20%. It explains why lung screening is offered to a defined high-risk group rather than to everyone.

Who is eligible now

The US Preventive Services Task Force recommends annual low-dose CT screening for adults aged 50 to 80 who have a 20 pack-year smoking history and who currently smoke or quit within the past 15 years.

A pack-year means one pack a day for a year. Twenty pack-years could be a pack a day for twenty years, or two packs a day for ten.

USPSTF adds that screening should stop once a person has gone 15 years without smoking, or develops a health problem that substantially limits life expectancy or the ability or willingness to have lung surgery. That last clause is the honest one: screening only helps if the finding can be acted on. Our guide to lung cancer screening covers what the appointment involves.

What is at stake

The American Cancer Society estimates 229,410 new US lung and bronchus cancer diagnoses and 124,990 deaths in 2026, a projection SEER republishes. Five-year relative survival across all stages, for 2016 to 2022, is 29.5%.

By stage, in that same 2016 to 2022 cohort: 65.5% for localized disease still in the lung, 38.2% for regional disease, and 10.5% for distant disease. Only 24% of cases are found while localized. Fifty-one percent are already distant.

Moving people from that last row to the first is the entire purpose of screening. These figures describe groups over past years and do not predict any individual's course. Our page on lung cancer has more.

When to get checked

Screening is for people without symptoms who meet the eligibility criteria. Symptoms are a separate track, and a normal screen last year does not cancel them:

• A cough lasting more than three weeks, or a change in a long-standing cough
• Coughing up blood, even once
• Breathlessness that is new or worsening
• Chest or shoulder pain that persists
• Repeated chest infections
• Unexplained weight loss or persistent fatigue

If you smoke, stopping does more than any scan can. Our guide to quitting smoking covers what actually works.

What this does not mean

• A 20% relative reduction is not a 20% chance of being saved. It means one in five lung cancer deaths in this high-risk group was prevented.
• The 96.4% false-positive rate is the main harm. Anyone accepting a screen should expect a possible callback that turns out to be nothing.
• NLST enrolled people at high risk of lung cancer by age and smoking history. It says nothing about screening people at average risk.
• Some cancers found by screening would never have caused harm. There is no test that tells you which ones.
• Screening does not undo the risk from smoking. It runs alongside stopping, not instead of it.

Sources

• New England Journal of Medicine (record via PubMed), Reduced Lung-Cancer Mortality with Low-Dose Computed Tomographic Screening — https://pubmed.ncbi.nlm.nih.gov/21714641/
• NCI, National Lung Screening Trial (NLST) — https://www.cancer.gov/types/lung/research/nlst
• USPSTF, Lung Cancer: Screening — https://www.uspreventiveservicestaskforce.org/uspstf/recommendation/lung-cancer-screening
• SEER Cancer Stat Facts, Lung and Bronchus Cancer — https://seer.cancer.gov/statfacts/html/lungb.html

How this article was prepared

An AI-assisted editorial system helped prepare this page. No named medical reviewer has reviewed it unless one is listed.

The National Cancer Information Foundation publishes Cancer Explained. This page is for learning. It is not medical advice and does not suggest a test or treatment.

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