What Is a Lung Nodule?

Hearing your healthcare provider say that you have a lung nodule may sound scary. Small lesions are common and usually aren't worrisome. About 95% of lung nodules found on first-time CT scans of current and former smokers who are between age 50 and 75 are not cancerous. However, it’s essential to follow through on getting a diagnosis, even if you’ve never smoked.

This article will explain what causes lung nodules, how they are diagnosed, the risk of your lung nodule being cancerous, and how they are treated.

lung nodule causes

Verywell / Emily Roberts


Lung nodules look like "spots" on X-rays and CT scans. They are sometimes also referred to as "coin lesions" because they often have a round, coin-like shape.

Lung nodules are defined as being three centimeters (cm) or 1.2 inches in diameter or less. They need to be at least 1 cm in size before they can be seen on a chest X-ray. CT scans provide more finely detailed images and can detect nodules as small as 1 to 2 millimeters.  

Lesions larger than 3 cm are referred to as lung masses, not nodules, and have a greater risk of being cancerous.


Lung nodules are common. They are found on one in 500 chest X-rays and one in 100 chest CT scans. Approximately 150,000 lung nodules are detected in people in the U.S. each year. Roughly half of adults who get a chest X-ray or CT scan have them.


Lung nodules are so small that they don't tend to cause breathing problems or other symptoms. That's why they're usually found incidentally when a chest X-ray is done for some other reason.

If symptoms are present, they may include:

  • A cough
  • Coughing up blood
  • Wheezing
  • Shortness of breath, often mild at first and only with activity
  • Respiratory infections, especially if the nodule is located near a major airway


Lung nodules can be benign (noncancerous) or malignant (cancerous). Most benign lung nodules result from inflammation due to infections or illnesses.

When your lungs become inflamed, tiny masses of tissue can develop.  Over time, the clumps can harden into a nodule on your lung.

The causes of most benign lung nodules include;

  • Infections, including bacterial infections such as tuberculosis and pneumonia; fungal infections from inhaling spores found in bird or bat droppings, or moist soil, wood, and leaves; and parasitic infections such as roundworms and tapeworms
  • Inflammation from irritants in the air, air pollution, or autoimmune conditions such as rheumatoid arthritis or sarcoidosis
  • Scarring from surgery or chest radiation

Other, less-common causes of a lung nodule include:

  • Pulmonary infarctions: Areas of lung tissue that have lost their blood supply
  • Arteriovenous malformations: A type of blood vessel abnormality
  • Atelectasis: Collapse of part of a lung
  • Pulmonary fibrosis: Thickening, scarring of lung tissue
  • Amyloidosis: Build-up of a kind of protein in the lung

The most common causes of malignant lung nodules are primary lung cancer that started in the lung or metastatic cancers from other regions of the body that have spread to the lungs.

  • Malignant tumors: Cancers that are often first detected as nodules include lung cancer, lymphomas, and sarcomas.
  • Metastases: Breast cancer, colon cancer, bladder cancer, prostate cancer, and other cancers can spread to the lungs. When a nodule is due to metastasis from another cancer, there are often multiple lung nodules present.

Carcinoid tumors, a kind of neuroendocrine tumor, are usually benign tumors except in rare cases when the tumor is metabolically active and called malignant carcinoid. 


There are three diagnoses for lung nodules; noncancerous, cancerous, or indeterminate. Indeterminate nodules cannot be definitively defined as benign or malignant.

When healthcare providers see a lung nodule on an X-ray, the first thing they usually do is get any lung imaging tests you may have had in the past to compare them.

If the nodule has been there for a long time and hasn't changed, it's probably not cancer. Further tests may not be needed. However, if you don’t have any prior X-rays for comparison, or if the nodule has changed or is new, further tests may be needed.

Your healthcare provider will also get a detailed medical history from you, which includes a history of your risk factors.

Examples of some of the questions you might be asked include:

  • Do you smoke? Have you ever smoked?
  • Have you had tuberculosis, pneumonia, surgery, or chest radiation?
  • What kind of work do you do?
  • Have you been exposed to asbestos or radon?
  • Do you work outdoors?
  • Where have you traveled?

For example, if you work outdoors with moist wood or soil, live in the southwest, or have traveled to certain countries, a fungal or parasitic infection may be considered as the potential cause of your lung nodule. Whereas if you smoke or used to smoke, a malignant tumor could be a possibility.

If a nodule does not appear to have changed or your healthcare providers believe that there's a low risk of it being cancer, they may take a "wait and watch" approach. They will have you get another imaging test, usually in six months to a year. Single, solitary nodules that have remained unchanged for two or more years do not generally need any further workup.

Imaging Tests

If your nodule is found on a chest X-ray, you may have a computed tomography (CT) scan of your chest. CT scans can provide detailed images and are taken at different angles.

Other tests healthcare providers may order include:

  • PET (positron emissions tomography) scan: A PET scan is a functional test that assesses things like the metabolic activity of the nodule. These tests are especially helpful for people who have had previous chest radiation, lung infections, or surgery, which may result in scar tissue. 
  • MRI (magnetic resonance imaging): This imaging test uses magnetic fields and radio frequencies and it is rarely used for evaluating lung nodules.

The number of lung nodules that are read by radiologists as indeterminate has increased with the use of lung cancer screening. Hearing that your nodule or nodules are indeterminate can be confusing.

It is often uncertain whether the nodule is malignant or benign based on imaging alone. It often needs to be further assessed by biopsy.


If your nodule has changed in size or appearance, if your diagnosis is uncertain, or if there's a chance that your nodules might be metastatic cancer from another tumor, a sample of your nodule may be required to determine whether it is malignant.

There are different biopsy methods:

  • Needle Biopsy: You'll be given a local anesthetic. Your healthcare provider will use CT scan images or live imaging to guide a small needle through your chest to get a tissue sample of your lung nodule.
  • Bronchoscopy: You'll receive light or conscious sedation. Your healthcare provider will run a long, thin fiberoptic tube with a surgical cutting tool on the end of it down your throat and into your lung to get a sample of your nodule for lab analysis.
  • VATS Biopsy: You're given a general anesthetic. Healthcare providers use a special kind of video to assist in inserting a tube through the chest wall to get a sample of your lung nodule tissue for analysis. They can also remove the entire lung nodule with this method.

Research suggests that even when a lung nodule is found in a person who might be expected to have lung metastases, only half of the nodules were found to be metastases when biopsied. Up to 25% were primary lung cancer. 


To diagnose a lung nodule, your healthcare provider will ask you about your history and risk factors. If the nodule was found on an X-ray, you may need other imaging tests to get more detailed pictures. In some cases, a sample of the nodule must be examined to confirm the diagnosis.

Risk of Cancer

Overall, there's a 60% chance that a lung nodule detected on an X-ray will be benign. There's a 99% chance that a lung nodule found on a CT scan is not cancerous.

However, a person's actual risk depends on a variety of factors. In smokers younger than 35, the chance that a lung nodule is malignant is less than 1%, while half of all lung nodules in smokers over age 50 are cancerous.

Where you live and have traveled can play a role, too. For example, studies have found that lung nodules due to schistosomiasis, a parasitic infection, are fairly common in African immigrants. Likewise, nodules caused by fungal infections such as coccidioidomycosis are common in the Southwest.

Here are other factors that can play a role in whether lung nodules that show up on an X-ray are noncancerous or cancerous.

Low Risk of Lung Cancer
  • Under age 35

  • Nodule is small (less than 3 cm in diameter)

  • Patient is a nonsmoker (and has never smoked)

  • No exposure to toxins in the workplace

  • No history of lung cancer among family members

  • No other signs or symptoms of lung cancer

  • Nodules are smooth and round in shape

  • Nodules are only partly solid

  • Nodules do not get bigger over time

  • Nodules are calcified (contain calcium deposits)

  • Interior of nodule is "cavitary"—darker on X-rays

  • Only one or a few nodules are present

High Risk of Lung Cancer
  • Over age 50

  • Nodule is larger than 3 cm in diameter

  • Patient smokes or is a former smoker

  • Exposure to occupational toxins such as asbestos or radon

  • First- or second-degree relative with lung cancer

  • Presence of lung cancer symptoms such as persistent cough or shortness of breath

  • Nodules are "spiculated"—have irregular or lobe-shaped borders

  • Nodules are solid

  • Nodules grow rapidly (on average doubling in size in four months)

  • Nodules show no signs of calcification

  • Nodules are not cavitary

  • Presence of multiple nodules (may indicate cancer metastases to the lungs)

Lung Cancer Screening

Lung cancer screening has been found to decrease the mortality rate from lung cancer by 20%. 

U.S. health officials recommend that if you're between the ages of 50 and 80, if you still smoke, if you have quit within the last 15 years, or you have a 20 pack-year smoking history, you should get screened every year for lung cancer.

Pack-year smoking history is a way to gauge how much you've smoked in your lifetime. It means that if you smoked one pack a day for 20 years or two packs a day for 10 years, you should get tested every year for lung cancer.

The recommendations call for using low-radiation-dose CT scans. Screening with chest X-rays has not been shown to reduce the risk of dying from lung cancer.

As with any screening test, there is a risk of false positives, and it's common to find nodules on CT screening. Finding nodules does not always mean cancer. In fact, studies thus far estimate that only around 5% of nodules found on a first lung CT scan screening for smokers are cancerous.


If you're between the ages of 50 and 80, you smoke, you quit within the last 15 years, or you have a 20 pack-year smoking history, you should be screened for lung cancer every year. A 20 pack-year smoking history means that you smoked one pack of cigarettes a day for 20 years, or two packs a day for 10 years.


The treatment of lung nodules varies widely depending on the diagnosis. Most benign lung nodules can be left alone, especially those seen on previous imaging tests that haven’t changed for two or more years.

If your nodule is cancerous, detection at this small size is very curable. In fact, treatment and survival rates for lung cancer, in general, have improved significantly in the past few years.


Nodules are "spots" in the lungs that are 3 cm in size or smaller. Most nodules are not cancerous and are caused by things like infection or scarring. They are more likely to be cancerous in people over age 50 and those who have smoked. Lung cancer screening is recommended for certain people who have a high risk of lung cancer.

A Word From Verywell

If you've heard that you or a loved one have a lung nodule, you are probably feeling a combination of nervous and overwhelmed. There are so many different possibilities for diagnosis, and some are frightening.

As you undergo testing and wait for your diagnosis, it may help to know that most lung nodules are not cancer.

If your lung nodule is cancerous, it may be very curable. New technologies and treatments have significantly improved survival rates for people with lung cancer.

And if your nodule turns out to be lung cancer, reach out to family and friends for support and help. There is also an active lung cancer community that will welcome you.

Frequently Asked Questions

  • Can pneumonia cause lung nodules?

    Yes, pneumonia can cause lung nodules to form. Certain risk factors such as older age, smoking status, and history with cancer can affect the likelihood of a lung nodule forming.

  • Can lung nodules disappear?

    It is very unlikely a lung nodule will disappear on its own. However, most lung nodules diagnosed using a CT scan are benign. A healthcare provider is able to determine if the lung nodule is cancerous by watching its growth over time and performing a biopsy (retrieving a sample). If the lung nodule is noncancerous, it might be able to be left alone.

  • Is a 7 mm lung nodule big?

    No, a 7 millimeter (mm) lung nodule is not big. Lung nodules that are less than 9 mm in size can be considered small, and are not usually cancerous. On average, only five out of 100 small lung nodules will become cancerous.

12 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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Additional Reading

By Lynne Eldridge, MD
 Lynne Eldrige, MD, is a lung cancer physician, patient advocate, and award-winning author of "Avoiding Cancer One Day at a Time."