A lung nodule is a small spot on the lung, typically round or oval, that shows up on a chest CT scan or X-ray. By definition, lung nodules measure 3 centimeters (about 1.25 inches) or less across. Anything larger is classified as a lung mass. The vast majority of lung nodules are not cancer, and most people never know they have one until it appears on imaging done for an unrelated reason.
How Common Lung Nodules Are
Lung nodules are extremely common. In a large study of non-smokers who received CT scans, 42% of participants had at least one lung nodule, with men (47.5%) slightly more likely than women (37.7%) to have one. Most of these nodules are small, harmless, and never grow or cause problems. If you’ve been told you have a lung nodule, you’re in very common company.
What Causes Them
The most common type of benign lung nodule is an infectious granuloma, a small cluster of immune cells that forms in response to a past infection. Fungal lung infections and tuberculosis are frequent culprits. Your body walls off the infection, and the resulting scar tissue shows up as a small spot on imaging, sometimes years or decades later. You may have had the infection without ever feeling sick enough to see a doctor.
Other causes include:
- Autoimmune-related granulomas. Conditions like rheumatoid arthritis and sarcoidosis can trigger immune cell clusters in lung tissue.
- Benign tumors. Noncancerous growths such as hamartomas (the most common benign lung tumor) can appear as nodules.
- Scarring. Smoking, inhaling chemical irritants, or past lung inflammation can leave behind small areas of scar tissue.
- Cancer. A small percentage of lung nodules are malignant, either as a primary lung cancer or as a spot that has spread from cancer elsewhere in the body.
Why Most Nodules Don’t Cause Symptoms
Lung nodules almost never cause symptoms on their own. They’re too small to block airways or interfere with breathing. That’s why they’re nearly always found incidentally, during a CT scan ordered for something else entirely, like chest pain, a car accident, or a preoperative workup. If you’re experiencing a cough, shortness of breath, or chest pain, those symptoms are far more likely caused by whatever prompted the scan in the first place, not by the nodule itself.
What Makes a Nodule More or Less Suspicious
When radiologists and doctors evaluate a lung nodule, they look at several characteristics on the CT scan to estimate the chance it could be cancerous. Not all nodules carry the same level of concern.
Features that raise suspicion include:
- Size. Larger nodules carry higher risk. A nodule under 6 millimeters is very unlikely to be cancer.
- Borders. Smooth, well-defined edges are reassuring. Spiculated borders (spiky, starburst-like edges) or irregular shapes are more concerning.
- Density. Nodules can be solid, partly solid, or have a hazy “ground-glass” appearance. Partly solid (subsolid) nodules are actually more likely to be cancerous than completely solid ones.
- Location. Nodules in the upper lobes of the lungs have a slightly higher association with malignancy.
- Calcification pattern. Nodules that are uniformly calcified (bright white on a scan) are almost always benign. Eccentric or off-center calcification is more worrisome.
- Growth rate. Cancerous nodules typically double in volume somewhere between one month and one year. A nodule that hasn’t changed over two or more years is very likely benign.
Your personal risk factors also matter. A history of smoking, older age, a family history of lung cancer, or exposure to asbestos or radon all shift the probability upward. A 35-year-old nonsmoker with a 4-millimeter smooth nodule is in a very different risk category than a 65-year-old with a 40-pack-year smoking history and an 8-millimeter spiculated nodule.
How Nodules Are Monitored
For most small lung nodules, the recommended approach is simply watching and waiting with repeat CT scans. The widely used Fleischner Society guidelines, published in 2017, provide a framework that most doctors follow. The timeline depends on size and risk.
For solid nodules smaller than 6 millimeters in a low-risk person, no routine follow-up may be needed at all. If there are risk factors like upper-lobe location or a suspicious shape, a single follow-up scan at 12 months is typically recommended. For solid nodules between 6 and 8 millimeters, guidelines recommend a follow-up CT scan at 6 to 12 months regardless of risk level, with possible additional scans after that depending on what’s seen.
Larger nodules, or those with worrisome features, may move to a shorter follow-up interval or jump straight to further evaluation. The goal of monitoring is straightforward: if the nodule doesn’t grow over time, it’s almost certainly benign. If it does grow, it can still be caught and treated early.
When Further Testing Is Needed
If a nodule is large enough, growing, or has suspicious features, your doctor may recommend a biopsy to get a definitive answer. Several approaches exist, and the choice depends on where the nodule is located and how accessible it is.
A needle biopsy is the least invasive option. Using CT guidance, a radiologist passes a thin needle through the chest wall and into the nodule to collect a tissue sample. This is done with local anesthesia, and you’re awake for it. It works best for nodules that sit near the outer edges of the lung.
For nodules deeper in the lung or near the airways, a transbronchial biopsy may be preferred. A thin, flexible scope is threaded through your mouth or nose, down your airway, and into the lung passages. Small tools passed through the scope can reach the nodule and take a sample.
In some cases, a surgical biopsy is necessary. Video-assisted thoracic surgery (VATS) uses small incisions and a camera to access the chest cavity. This approach can both biopsy and remove a nodule in the same procedure, making it useful when the suspicion for cancer is high enough that removal is likely the next step regardless of results. An open surgical biopsy, involving a larger incision, is reserved for situations where less invasive options aren’t feasible.
What Happens if a Nodule Is Cancerous
Lung cancer caught at the nodule stage is typically early-stage cancer, and early-stage lung cancer has a significantly better prognosis than cancer found after symptoms develop. A small cancerous nodule confined to the lung can often be removed surgically with excellent long-term outcomes. This is one of the key reasons lung cancer screening programs exist for high-risk individuals: finding cancer when it’s still a tiny nodule, before it spreads, changes the entire trajectory of treatment.
If your scan shows a lung nodule, the most likely outcome by far is that it’s benign and will never require treatment. The monitoring process exists to catch the uncommon cases where something more is going on, and to catch them early enough to make a real difference.