The National Lung Screening Trial (NLST) studied older people with a history of heavy smoking. The tables below show how the results of the NLST study might affect a group of 1,000 people who are at high risk for lung cancer and who choose to have yearly screening with CT scans.1
Benefits of yearly lung cancer screening*
||Annual screening for 3 years
||No annual screening
|People who died of lung cancer within 6½ years
||18 out of 1,000
||21 out of 1,000
*Based on the best available evidence (evidence quality:high
Risks of yearly lung cancer screening*
|People who got abnormal test results that proved to be wrong after more testing (false-positives)
||365 out of 1,000
|People who had an invasive procedure because of a false-positive result
||25 out of 1,000
|People who had a major complication from a procedure they had because of a false-positive result
||3 out of 1,000
|Estimated number of people who would get cancer treatment they didn't actually need (overdiagnosis)
||About 4 out of 1,000footnote 2
*Based on the best available evidence (evidence quality: high)
The quality of the evidence about the benefits of lung cancer screening is moderate.
For heavy smokers who qualify for annual screening, having this regular test offers them a better chance of not dying of lung cancer.
Take two groups of 1,000 people. One group has annual screening for 3 years, and one group does not. About 6½ years later, about 18 people in the screening group and about 21 people in the non-screening group will have died of lung cancer. That means the group that did not have annual screening had 3 more lung cancer deaths than the screening group.
But this is just an average. The higher your cancer risk, the more likely it is that annual screening will prevent death from lung cancer. The more pack years in your smoking history, the higher your lung cancer risk.
The quality of the evidence about lung cancer screening risks is moderate.
False-positive result and follow-up. A CT scan will find nodules or other problems that aren't cancer. This is called a false-positive result. This could cause you to have other tests or treatments that it turns out you didn't need, and they could cause their own problems.
Take a group of 1,000 people who have annual lung cancer screening. About 365 of them will have at least one false-positive result. Of the 1,000 people tested, 25 will have an invasive procedure, such as a lung biopsy, because of a false-positive result. And 3 out of 1,000 will have a major complication because of that procedure. Major complications include collapsed lung, major bleeding, and, in rare cases, death.
Overdiagnosis. Screening may find cancers that might never be life-threatening. This is called overdiagnosis. It could cause you to have treatment you don't need. And that treatment could cause its own problems.
Take a group of 1,000 people who have annual lung cancer screening. Experts estimate that about 4 of them will get cancer treatment they didn't actually need.
Radiation-caused cancer. There is a very small chance that the extra radiation exposure from annual lung cancer screening could cause a fatal cancer.
Understanding the evidence
Some evidence is better than other evidence. Evidence comes from studies that look at how well treatments and tests work and how safe they are. For many reasons, some studies are more reliable than others. The better the evidence is—the higher its quality—the more we can trust it.
The information shown here is based on the best available evidence. The evidence is rated using four quality levels: high, moderate, borderline, and inconclusive.
Another thing to understand is that the evidence can't predict what's going to happen in your case. When evidence tells us that 2 out of 100 people who have a certain test or treatment will have a certain result and that 98 out of 100 will not, there's no way to know if you will be one of the 2 or one of the 98.