Most lung nodules are not cancer: at least 19 in 20 are benign, and most are the scar of an old infection or a small lymph node [1]. Size is the most important clue: a nodule smaller than 6 mm has less than a 1 in 100 chance of being cancer and needs no follow-up in people at low risk; a 6 to 8 mm nodule is checked with a CT scan 6 to 12 months later; and a nodule larger than 8 mm may need a CT scan at 3 months, a PET scan or a biopsy [1, 2]. Growth, a large solid part in a ground-glass nodule and spiculated edges make cancer more likely [2, 4].
Key points
- Lung nodules are very common: they are seen on about one in three chest CT scans [1, 6].
- At least 19 in 20 nodules are not cancer; the smaller the nodule, the more likely it is benign [1].
- A solid nodule smaller than 6 mm, such as a 4 mm nodule, needs no routine follow-up in people at low risk [2].
- Growth on later CT scans, a large solid part in a ground-glass nodule and spiculated edges are signs that need further checks [2, 3, 4].
- The most important thing you can do: do not miss the follow-up CT scan at the time your doctor gave you, and bring your earlier results [2, 3].
What is a lung nodule? A nodule found on a CT scan
A lung nodule is a small, round spot in the lung seen on a CT scan or chest X-ray. A nodule is up to 3 cm across; a spot larger than 3 cm is called a "mass" [11].
Nodules are very common and are usually found on a CT scan done for another reason [6]. As more CT scans are done, more nodules are found, but the number of lung cancers has not gone up [6].
Most nodules are benign [1]. The most common causes are:
What size lung nodule is concerning?
Size is the most important clue. The radiologist reports the size of the nodule in millimetres. The table below is for a solid nodule found by chance in an adult, not for someone with a known cancer or a weakened immune system [2].
| Size of solid nodule | Chance of cancer | Usual next step |
|---|---|---|
| Smaller than 6 mm | Less than 1 in 100 [1] | No routine follow-up for people at low risk; for people at high risk, perhaps one CT scan at 12 months [2] |
| 6 to 8 mm | About 1 to 2 in 100 [1] | A CT scan 6 to 12 months later, and often once more at 18 to 24 months [2] |
| Larger than 8 mm | Higher; it depends on the nodule and on the person [1, 8] | A CT scan at 3 months, a PET scan or a biopsy [2] |
| 10 mm or larger | In a study of smokers, about 1 in 7 [5] | Further tests without delay [5] |
"High risk" means, for example, a heavy smoking history or other risk factors; your doctor takes all of this into account [2].
Is a 4 mm lung nodule dangerous?
Usually not. Nodules smaller than 6 mm have a very low chance of being cancer [1]. In a large screening study of smokers, people with a nodule smaller than 5 mm developed lung cancer as often as people with no nodule at all: about 4 in 1000 people over 2 years [5].
So if you do not smoke and have no other risk factors, a 4 mm nodule usually needs no follow-up. If you have a heavy smoking history, or the nodule is in the upper part of the lung or has a suspicious shape, your doctor may ask for one CT scan at 12 months [2].
Ground-glass opacity: what does it mean?
"Ground glass" means an area of the lung that looks slightly hazier than normal, while the blood vessels and airways can still be seen through it. This finding has many causes, such as infection, inflammation, fluid or bleeding, and sometimes cancer [11].
- Pure ground-glass nodule: has no solid part. If it is smaller than 6 mm, it usually needs no follow-up. If it is 6 mm or larger, the CT scan is repeated 6 to 12 months later to see whether it is still there or has gone; if it remains, it is checked every 2 years until 5 years [2].
- Part-solid nodule: partly ground glass and partly solid. The larger the solid part, the higher the chance of cancer [1, 2].
A ground-glass nodule that persists and is larger than 1 cm is more likely to be cancer [1]. But a cancer that looks like a pure ground-glass nodule usually grows very slowly; that is why its follow-up is longer [1, 2].
Spiculated nodule or mass, and nodule growth: what do they mean?
"Spiculated" means that thin strands spread out from the edge of the nodule into the surrounding tissue. This appearance is more often seen in cancer, but on its own it is not a diagnosis [11]. Things that make cancer more likely [2, 4]:
- a larger nodule
- spiculated edges
- a part-solid nodule
- a nodule in the upper part of the lung
- growth on later CT scans
- older age, a smoking history, emphysema and a family history of lung cancer
On the other hand, a nodule with calcium in a benign pattern (for example in its centre, or looking like popcorn) is considered benign [8]. A solid nodule that has not changed for at least 2 years usually needs no further tests [8]. Doctors use these features in risk calculators to estimate the chance of cancer [4, 8].
Lung-RADS categories on a screening CT (for example, Lung-RADS 3)
If you have had a low-dose CT scan to screen for lung cancer, the end of the report gives a Lung-RADS number [3]. A "positive" screening result is frightening, but in a large study nearly all positive results (more than 9 in 10) were not cancer [7]. The table below explains each category in simple words.
| Lung-RADS category | Meaning | Usual next step |
|---|---|---|
| 0 | Incomplete; comparison with an earlier CT scan or more imaging is needed, sometimes because the finding looks like an infection [3] | Comparison with earlier images, or a repeat CT scan [3] |
| 1 and 2 | No nodule, or a nodule that looks or behaves benign; chance of cancer less than 1 in 100 [3] | Continue yearly screening [3] |
| 3 | Probably benign; chance of cancer 1 to 2 in 100 [3] | Low-dose CT scan in 6 months [3] |
| 4A | Suspicious; chance of cancer 5 to 15 in 100 [3] | Low-dose CT scan in 3 months; sometimes a PET scan [3] |
| 4B and 4X | Very suspicious; chance of cancer more than 15 in 100 [3] | Diagnostic CT scan, PET scan or biopsy [3] |
An "S" next to the number means that another important finding, not lung cancer, was also seen and needs follow-up [3].
When are a PET scan and a biopsy needed?
For most small nodules, the best step is to wait and repeat the CT scan to see whether the nodule grows [1, 2]. Small nodules are hard to biopsy, and a PET scan does not show them reliably [8].
- PET scan: mainly for a solid nodule larger than 8 mm with a low to moderate chance of cancer [8]. Read more: What is a PET scan?
- Biopsy: with a needle through the skin, or by bronchoscopy (a thin tube passed through the mouth into the lung). These methods do not always give a clear answer; sometimes a repeat biopsy or surgery is needed [1]. Worried about a biopsy? Read: Can a biopsy spread cancer?
- Surgery: when the chance of cancer is high, the nodule is sometimes removed straight away by surgery [1, 8].
The decision also depends on your age, other illnesses and your own wishes [1, 8]. See the overall diagnostic path in How is cancer diagnosed?
When should I call my doctor?
Most nodules cause no symptoms. If you have a nodule and notice any of these symptoms, do not wait for your follow-up appointment; see a doctor sooner [9]:
- coughing up blood
- a cough that does not go away or gets worse
- new shortness of breath or wheezing, or chest pain
- hoarseness
- unexplained loss of weight and appetite, or severe tiredness
- swelling of the face or the veins in the neck
Coughing up a lot of blood, or sudden severe shortness of breath, is an emergency; call your local emergency number. Read more: What are the symptoms of lung cancer?
Frequently asked questions
Is a lung nodule dangerous?
Most of the time, no. At least 19 in 20 nodules are benign [1]. But a few are early cancers; proper follow-up helps find these cancers early and spares benign nodules unnecessary tests [1]. Read more: Is lung cancer curable?
Can a lung nodule go away on its own?
Sometimes, yes. Some nodules, especially ground-glass ones, are caused by inflammation or infection and are no longer seen on the next CT scan; that is why the CT scan is repeated first for these nodules, to see whether they persist [2, 11]. A nodule that is the scar of an old infection usually stays but does not change [1, 8].
My nodule has not changed for 2 years: does it still need follow-up?
I have several small nodules in my lungs: is that worse?
Why doesn't the doctor do a biopsy straight away?
I smoke, or used to smoke: is my nodule more dangerous?
A smoking history, older age and emphysema make it more likely that a nodule is cancer [4]. If you are 50 to 80, have smoked at least 20 pack-years and still smoke or quit less than 15 years ago, a yearly low-dose CT scan to screen for lung cancer is recommended [10]. Check with the pack-year calculator. About quitting, read: How much does quitting smoking lower cancer risk? and Does hookah (shisha) cause cancer?
Don't all these follow-up CT scans mean a lot of radiation?
The follow-up intervals are set so that only the nodules that need it are checked, and only as often as needed; this is why very small nodules in people at low risk are not followed up [2]. About the radiation risk, read: Do CT scans cause cancer?
Nodule management by guideline (for doctors)
For physicians
| Nodule type | <6 mm (<100 mm3) | 6 to 8 mm (100 to 250 mm3) | >8 mm (>250 mm3) |
|---|---|---|---|
| Solid, single, low risk | No routine follow-up [2] | CT at 6 to 12 months, then consider CT at 18 to 24 months [2] | Consider CT at 3 months, PET/CT or tissue sampling [2] |
| Solid, single, high risk | Optional CT at 12 months [2] | CT at 6 to 12 months, then CT at 18 to 24 months [2] | Consider CT at 3 months, PET/CT or tissue sampling [2] |
| Solid, multiple | Low risk: no routine follow-up; high risk: optional CT at 12 months [2] | CT at 3 to 6 months, then CT at 18 to 24 months (low risk: consider) [2] | CT at 3 to 6 months, then CT at 18 to 24 months (low risk: consider) [2] |
| Pure ground glass, single | No routine follow-up [2] | ≥6 mm: CT at 6 to 12 months to confirm persistence, then every 2 years until 5 years [2] | ≥6 mm: CT at 6 to 12 months to confirm persistence, then every 2 years until 5 years [2] |
| Part-solid, single | No routine follow-up [2] | ≥6 mm: CT at 3 to 6 months; if unchanged and the solid component remains <6 mm, annual CT for 5 years; a solid component ≥6 mm is highly suspicious [2] | ≥6 mm: CT at 3 to 6 months; if unchanged and the solid component remains <6 mm, annual CT for 5 years; a solid component ≥6 mm is highly suspicious [2] |
| Subsolid, multiple | CT at 3 to 6 months; if stable, consider CT at 2 and 4 years [2] | ≥6 mm: CT at 3 to 6 months; further management based on the most suspicious nodule [2] | ≥6 mm: CT at 3 to 6 months; further management based on the most suspicious nodule [2] |
Size = average of long and short axes, rounded to the nearest millimetre. A solid nodule <6 mm in a high-risk patient with suspicious morphology or upper-lobe location may warrant 12-month follow-up [2].
Lung-RADS v2022 (LDCT screening). Category 2 (probability of malignancy <1%): solid <6 mm at baseline or new <4 mm, nonsolid <30 mm → annual LDCT. Category 3 (1 to 2%): solid 6 to <8 mm at baseline or new 4 to <6 mm, part-solid ≥6 mm with a solid component <6 mm, nonsolid ≥30 mm → LDCT at 6 months. Category 4A (5 to 15%): solid 8 to <15 mm, growing <8 mm or new 6 to <8 mm, solid component 6 to <8 mm → LDCT at 3 months; PET/CT may be considered if there is a solid nodule or solid component ≥8 mm. Category 4B (>15%): solid ≥15 mm, new or growing ≥8 mm, solid component ≥8 mm → chest CT, PET/CT and/or tissue sampling. 4X: category 3 or 4 with an additional suspicious feature (such as spiculation or lymphadenopathy). v2022 added guidance on atypical cysts, juxtapleural and airway-centred nodules, potentially infectious findings (category 0 with short-interval follow-up) and stepped management of stable or shrinking nodules [3]. In NLST, 24.2% of LDCT screens over three rounds were positive and 96.4% of them were false positives [7].
Probability of malignancy. At least 95% of nodules are benign (most often granulomas or intrapulmonary lymph nodes); <1% for nodules <6 mm and 1 to 2% for 6 to 8 mm; ground-glass nodules persisting beyond 3 months and larger than 10 mm 10 to 50%; sensitivity of bronchoscopy and transthoracic needle biopsy for lung cancer 70 to 90% [1]. NELSON (9681 non-calcified nodules in 7155 participants): 2-year lung cancer probability 0.6% for a volume ≤100 mm3 and 0.4% for a diameter <5 mm (similar to participants without nodules, 0.4%); 2.4% for 100 to 300 mm3 and 1.3% for 5 to 10 mm; 16.9% for ≥300 mm3 and 15.2% for ≥10 mm. In intermediate nodules, volume doubling time ≥600 days 0.8%, 400 to 600 days 4.0% and ≤400 days 9.9% [5]. Brock model (PanCan, 7008 nodules in 1871 people, 102 malignant; validated in BCCA): older age, female sex, family history of lung cancer, emphysema, larger size, upper lobe, part-solid type, lower nodule count and spiculation; AUC >0.90, even for nodules of 10 mm or smaller [4].
ACCP (2013). Solid nodule >8 mm with a pretest probability of 5 to 65%: functional imaging, preferably PET; with a probability >65%, PET should not be performed to characterise the nodule. Nodules ≤8 mm are not reliably characterised by PET. Solid nodule stable for at least 2 years: no further evaluation. Diffuse, central, laminated and popcorn calcification is considered benign. In a 2008 meta-analysis, pooled PET sensitivity was 95% and specificity 82% [8]. Fleischner is intended for adults aged 35 years or older [2]; incidental nodules were reported on 24 to 31% of chest CTs (2006 to 2012) [6].
Related cancer types
Related questions
References
11 referencesShow all references, 2 with a study cardClose the reference list
Numbers in the text, such as [1], refer to these sources. Sources with a “Study card” button are summarised in the site’s evidence library.
- 1
- 2
- 3
- 4
- 5
- 6
- 7Reduced lung-cancer mortality with low-dose computed tomographic screening
- 8
- 9Non-Small Cell Lung Cancer Treatment (PDQ®)–Patient Version
- 10Screening for Lung Cancer: US Preventive Services Task Force Recommendation Statement
- 11
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