Lung cancer screening results: Lung-RADS
A lung screening CT report gives one Lung-RADS category, from 0 to 4X, based on the most suspicious finding. Most scans land in category 1 or 2 and simply mean the next yearly scan. Categories 3 and 4 need a closer look, but most of those findings are not cancer. Your doctor explains your result and decides what comes next. (ACR Lung-RADS v2022) (USPSTF, 2021)
The categories
Timing counts from the date of the scan being read. The share of scans is the American College of Radiology's own estimate. (ACR Lung-RADS v2022)
| Category | Name | Usual next step | Share of scans |
|---|---|---|---|
| 0 | Incomplete: an older CT is being found for comparison, part of the lungs cannot be assessed, or findings suggest infection or inflammation | Compare with the older CT, more screening imaging, or a low-dose CT in 1 to 3 months | About 1% |
| 1 | Negative: no nodules, or a nodule with clearly benign features | Yearly screening CT in 12 months | 39% |
| 2 | Benign, based on how a finding looks or behaves | Yearly screening CT in 12 months | 45% |
| 3 | Probably benign | Low-dose CT in 6 months | 9% |
| 4A | Suspicious | Low-dose CT in 3 months; a PET/CT may be considered for a solid part of 8 mm or more | 4% |
| 4B | Very suspicious | A diagnostic chest CT, a PET/CT, a tissue sample or referral, depending on your health, your preferences and the likely risk | 2% |
| 4X | Category 3 or 4 with extra features that raise suspicion | Same as 4B | Under 1% |
| S | Modifier added to 0 to 4 for a finding not related to lung cancer that may matter | As fits that finding | 10% |
A 3 that is stable or smaller at the 6-month scan goes back to category 2. A 4A that is stable or smaller at the 3-month scan goes to category 3. If an older CT turns up, category 0 is replaced by a new category. (ACR Lung-RADS v2022)
The American College of Radiology counts categories 1 and 2 as a negative screen and 3 and 4 as a positive screen, and notes that a negative screen does not mean a person does not have lung cancer. (ACR Lung-RADS v2022)
Nodule size bands
Size is the average of the long and short width, in millimeters. For a solid nodule seen on the first screening scan, the bands are: (ACR Lung-RADS v2022)
| Solid nodule size | Category |
|---|---|
| Under 6 mm | 2 |
| 6 to under 8 mm | 3 |
| 8 to under 15 mm | 4A |
| 15 mm or more | 4B |
Smaller cutoffs apply to a new nodule on a later scan (for example, a new solid nodule under 4 mm is category 2). Part-solid and ground-glass (hazy) nodules, cysts and airway findings have their own rules. Growth means the average size rose by more than 1.5 mm within 12 months. The radiologist applies these rules; your report states the result. (ACR Lung-RADS v2022)
How often a positive result is a false alarm
Most positive screens are not cancer. In the National Lung Screening Trial, false-positive rates were 26.3% at the first scan, 27.2% at year 1 and 15.9% at year 2; in the NELSON trial they were 19.8% at the first scan. Both trials ran before Lung-RADS. One study found that using Lung-RADS on the NLST first-round scans would have lowered the false-positive rate to 12.8%, from 26.6%, at the cost of some missed cancers. (USPSTF, 2021)
In the NLST, false-positive results led to an invasive procedure in 1.7% of people screened, with complications in 0.1%. (USPSTF, 2021) More: false positives and overdiagnosis.
Findings not about lung cancer
The scan also shows the heart, aorta and upper abdomen. Common incidental findings include coronary artery calcium, aortic aneurysms, emphysema, and infection or inflammation, as well as lumps or cysts in organs such as the kidney, liver or thyroid. Studies reported significant incidental findings in 4.4% to 40.7% of people, partly because they defined them differently, and they were more common with older age. These findings can lead to more visits and tests, and the balance of benefit and harm from finding them is uncertain. (USPSTF, 2021) Lung-RADS marks them with the S modifier. (ACR Lung-RADS v2022)
The next yearly scan
After category 1 or 2, the next screening scan is 12 months from the date of this one. (ACR Lung-RADS v2022) Where bodies differ: the USPSTF advises yearly screening for adults 50 to 80 with a 20 pack-year history who smoke now or quit within the past 15 years, and stopping once a person has not smoked for 15 years. (USPSTF, 2021) The American Cancer Society's 2023 guideline covers people 50 to 80 with a 20 pack-year history who smoke or used to smoke, with no limit on years since quitting. (ACS, 2024) Both stress that screening does not replace quitting. (USPSTF, 2021) (ACS, 2024)
If you have symptoms that could be from lung cancer, see your doctor right away, whatever your last screening result was. Testing for symptoms is diagnosis, not screening. (ACS, 2024)
Questions people ask
What does Lung-RADS 2 mean?
Lung-RADS 2 means benign: a finding that looks harmless from its features or behavior. The American College of Radiology advises the next yearly screening scan, 12 months from the date of this scan. It is the most common result, at an estimated 45% of scans. (ACR Lung-RADS v2022)
Does Lung-RADS 3 or 4 mean I have cancer?
No. Categories 3 and 4 count as a positive screen and need a closer look, but most positive results turn out not to be cancer. In the NLST trial, false-positive rates were 26.3% at the first scan; a later analysis found that using Lung-RADS on the same scans would have cut the baseline false-positive rate to 12.8%. (ACR Lung-RADS v2022) (USPSTF, 2021)
Does a negative result mean I do not have lung cancer?
Not for certain. The American College of Radiology notes that a negative screen (category 1 or 2) does not mean a person does not have lung cancer, which is one reason the scan is repeated every year while you qualify. (ACR Lung-RADS v2022)
What is the S on my report?
S is a modifier added to categories 0 to 4 for a finding that may matter but is not related to lung cancer. The USPSTF lists coronary artery calcium, aortic aneurysms, emphysema and infection or inflammation among common incidental findings. (ACR Lung-RADS v2022) (USPSTF, 2021)
When is the next scan after a normal result?
After category 1 or 2, the next screening low-dose CT is due 12 months after the date of the scan. The USPSTF and the American Cancer Society both advise yearly screening while you qualify, but they set slightly different rules on who qualifies. (ACR Lung-RADS v2022) (USPSTF, 2021) (ACS, 2024)