Lung nodule found by chance: follow-up scans

The main guidance

The Fleischner Society published its guideline for nodules found by chance on CT in 2017. It aims to avoid follow-up scans for nodules with less than a 1% chance of cancer, and it is cited here through an open-access review published in 2025. (Fleischner 2017, open-access review) In the UK, the British Thoracic Society (BTS) guideline on pulmonary nodules was published in 2015. (BTS, 2015) The BTS has a draft update out for comments until 1 December 2026; until it is final, the 2015 guideline is the current one. (BTS consultation)

Who it applies to

The Fleischner guideline applies to adults aged 35 and older, because younger people have a low risk of cancer. It is not meant for lung cancer screening, for people with a recent cancer, or for people with a weakened immune system, where infection is more likely. (Fleischner 2017, open-access review) The BTS guideline covers adults aged 18 and older with one or more nodules, including people with a current or past cancer. (BTS, 2015)

Low and high risk

The Fleischner table splits adults into low and high risk and asks the doctor to weigh all relevant risk factors. The review lists factors linked to a higher chance of lung cancer: older age (risk rises with each decade after 35 to 40), smoking, a family history of lung cancer, emphysema or scarring (fibrosis) of the lung, and a nodule that is larger, has spiky or irregular edges, or sits in an upper lobe. (Fleischner 2017, open-access review) For nodules 8 mm or larger, the BTS uses a risk tool (the Brock model) that combines features of the person and the nodule to estimate the chance of cancer. (BTS, 2015)

Solid nodules: Fleischner 2017

Size is the average of the long and short width, rounded to the nearest millimeter. For a single solid nodule, the table lists: (Fleischner 2017, open-access review)

Fleischner Society 2017, single solid nodule found by chance in an adult
Size	Low risk	High risk
Under 6 mm	No routine follow-up	Optional CT at 12 months
6 to 8 mm	CT at 6 to 12 months, then consider CT at 18 to 24 months	CT at 6 to 12 months, then CT at 18 to 24 months
Over 8 mm	Consider CT at 3 months, PET/CT or other tests	Consider CT at 3 months, PET/CT or other tests

For several solid nodules 6 mm or larger, the table lists CT at 3 to 6 months, then a CT at 18 to 24 months (for low risk, consider it), with management guided by the most suspicious nodule. (Fleischner 2017, open-access review)

Ground-glass and part-solid nodules: Fleischner 2017

A subsolid nodule looks hazy (ground glass), or partly hazy and partly solid (part solid). The table lists: (Fleischner 2017, open-access review)

Fleischner Society 2017, single subsolid nodule found by chance in an adult
Type	Under 6 mm	6 mm or larger
Ground glass	No routine follow-up (for some suspicious nodules, consider CT at 2 and 4 years)	CT at 6 to 12 months to confirm it is still there, then CT every 2 years until 5 years
Part solid	No routine follow-up	CT at 3 to 6 months to confirm it is still there; if unchanged and the solid part stays under 6 mm, CT every year for 5 years

For several subsolid nodules under 6 mm, the table lists CT at 3 to 6 months and, if stable, CT at 2 and 4 years to consider. The review says a ground-glass nodule can still grow after 5 years of being stable. (Fleischner 2017, open-access review)

What the BTS lists

No follow-up: nodules under 5 mm or under 80 mm3; nodules with a typical harmless pattern of calcium or fat; and typical small smooth nodules next to a lung fissure or the lung lining. (BTS, 2015)
CT follow-up: nodules from 5 mm to under 8 mm, or 80 to under 300 mm3. Growth is checked with repeat CT at 3 months and 1 year (at 1 year for nodules of 5 to under 6 mm), with a 25% or larger change in volume counted as growth. (BTS, 2015)
Larger nodules: for nodules 8 mm or larger, a risk estimate guides the next step; CT follow-up is considered when the chance of cancer is under 10%, and a PET-CT is offered when it is over 10%. (BTS, 2015)
Subsolid nodules: a repeat thin-section CT at 3 months for all, because some go away; then, if the risk is under about 10%, repeat low-dose CT at 1, 2 and 4 years from the first scan. (BTS, 2015)

How long follow-up lasts

The BTS discharges people with solid nodules that are stable (less than a 25% change in volume) on CT after 1 year, and advises 2 years of CT follow-up when only width is measured. For very slow-growing nodules, it says ending or continuing scans depends on the person's wishes, fitness and age. (BTS, 2015) MedlinePlus says a nodule that has not changed in size over 2 years is most likely benign and often needs nothing more. (MedlinePlus) Fleischner follow-up for solid nodules runs out to 18 to 24 months, and for subsolid nodules up to 5 years. (Fleischner 2017, open-access review)

How this differs from Lung-RADS in screening

The Fleischner review says its guideline should not be used in lung cancer screening programs, which use Lung-RADS because they are designed for people at high risk. (Fleischner 2017, open-access review) The BTS guideline says to use the same approach for nodules found by chance and through screening. (BTS, 2015) For the screening categories and timing, see lung cancer screening results: Lung-RADS; for the scan itself, see low-dose CT lung scan: what to expect.

Routine age-based screening

A nodule found by chance does not replace the routine screenings for your age. For who is offered yearly lung cancer screening, see lung cancer screening and screenings if you smoke; for the rest, see screenings by age and gender.

Where they differ:

Smallest size followed. Fleischner sets no routine follow-up below 6 mm (100 mm3) for low-risk adults; (Fleischner 2017, open-access review) the BTS starts CT follow-up at 5 mm (80 mm3). (BTS, 2015)
Solid nodules. Fleischner lists scans out to 18 to 24 months; (Fleischner 2017, open-access review) the BTS discharges a stable solid nodule after 1 year when volume is measured. (BTS, 2015)
Subsolid nodules. Fleischner follows ground-glass and part-solid nodules 6 mm or larger to 5 years; (Fleischner 2017, open-access review) the BTS lists scans at 3 months and at 1, 2 and 4 years when the risk is low. (BTS, 2015)
Screening scans and age. Fleischner is for adults 35 and older and not for screening; (Fleischner 2017, open-access review) the BTS covers adults 18 and older and treats screening and chance findings the same way. (BTS, 2015)

Your doctor decides what your result means for you.

Questions people ask

Is a lung nodule found by chance usually cancer?

Usually not. The Fleischner Society set its 2017 guideline so that nodules with less than a 1% chance of cancer are not followed with more scans. MedlinePlus says a nodule is more likely benign when it is small, smooth and solid and the person is young and never smoked. (Fleischner 2017, open-access review) (MedlinePlus)

Does a small nodule need a follow-up scan?

Often not. The Fleischner Society advises no routine follow-up for a single solid nodule under 6 mm in a low-risk adult, with an optional CT at 12 months for higher-risk adults. The British Thoracic Society advises no follow-up for nodules under 5 mm or under 80 mm3. (Fleischner 2017, open-access review) (BTS, 2015)

How long does follow-up last?

For a solid nodule, Fleischner lists scans out to 18 to 24 months; the BTS discharges a solid nodule that is stable after 1 year when volume is measured, or after 2 years when only width is measured. Hazy (ground-glass) and part-solid nodules are followed longer: up to 5 years under Fleischner and to 4 years under the BTS. (Fleischner 2017, open-access review) (BTS, 2015)

Is this the same as a Lung-RADS result?

No. The Fleischner guideline is for nodules found by chance and is not meant for lung cancer screening, which uses Lung-RADS. The BTS guideline uses the same approach for nodules found by chance and through screening. (Fleischner 2017, open-access review) (BTS, 2015)

Does the guidance apply to everyone?

No. The Fleischner guideline applies to adults aged 35 and older and not to people with a weakened immune system or a known cancer. The BTS guideline covers adults aged 18 and older. (Fleischner 2017, open-access review) (BTS, 2015)