What Are the Chances a Lung Nodule Is Cancer?

Symptoms, Causes & Treatment

Doctor looking at chest x-ray
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If you have been told you have a lung nodule or lung nodules on an x-ray, it can be very frightening. What are some causes? How common are they? And what are the chances it's lung cancer?

While the majority (at least 60 percent) of lung nodules are due to benign (not cancerous) conditions, it is important to work with your doctor to determine the cause. When lung cancer is caught early and is still small, there is a greater chance that it can be cured.

Definition of Lung Nodules

A lung nodule is defined as a “spot” on the lung that is 3 centimeters (about 1.5 inches) in diameter or less. If an abnormality is seen on an x-ray of the lungs that is larger than 3 cm, it is considered a “lung mass” instead of a nodule and is more likely to be cancerous. Lung nodules usually need to be at least 1 cm in size before they can be seen on a chest x-ray.

How Common Are Lung Nodules?

Lung nodules are quite common and are found on one in 500 chest x-rays, and one in 100 CT scans of the chest. Approximately 150,000 lung nodules are detected in people in the United States each year. Roughly half of people who smoke over the age of 50 will have nodules on a CT scan of their chest.

What Are the Chances It's Cancer?

Overall, the likelihood that a lung nodule is cancer is 40 percent, but the risk of a lung nodule being cancerous varies considerably depending on several things.

In people less than 35 years of age, the chance that a lung nodule is cancer is less than 1 percent, whereas half of lung nodules in people over age 50 are malignant (cancerous). Other factors that raise or lower the risk that a lung nodule is cancer include:

  • Size - Larger nodules are more likely to be cancerous than smaller ones.
  • Smoking - Current and former smokers are more likely to have cancerous lung nodules than never smokers. Learn the percentage of smokers who get lung cancer.
  • Occupation - Some occupational exposures raise the likelihood that a nodule is cancer.
  • Medical history - Having a history of cancer increases the chance that it could be malignant.
  • Shape - Smooth, round nodules are more likely to be benign, whereas irregular or “spiculated” nodules are more likely to be cancerous.
  • Growth - Cancerous lung nodules tend to grow fairly rapidly with an average doubling time of about four months, while benign nodules tend to remain the same size over time.
  • Calcification - Lung nodules that are calcified are more likely to be benign.
  • Cavitation - Nodules described as “cavitary,” meaning that the interior part of the nodule appears darker on x-rays, are more likely to be benign.

Causes of Lung Nodules

Lung nodules can be either benign (non-cancerous) or malignant (cancer). The most common causes include granulomas (clumps of inflamed tissue) and hamartomas (benign lung tumors).

The most common cause of malignant lung nodules includes lung cancer or cancer from other regions of the body that have spread to the lungs (metastatic cancer). These nodules can be broken down into a few major categories:

  • Infections - This includes bacterial infections such as tuberculosis, fungal infections such as histoplasmosis and coccidiomycosis, and parasitic infections such as ascariasis (roundworms).
  • Inflammation - Conditions such as rheumatoid arthritis, sarcoidosis, and Wegener's granulomatosis can cause nodules.
  • Benign tumors - Benign lung tumors such as hamartomas can show up as a nodule in the lungs on x-ray.
  • Malignant tumors – This includes lung cancer, lymphomas, and cancer that has spread to the lungs from other parts of the body. The chance that a nodule is lung cancer is greater if other signs or symptoms of lung cancer are present.

Nodules Detected on Lung Cancer Screening

Lung cancer screening in appropriate people has been found to decrease the mortality rate from lung cancer by 20 percent. But as with any screening test, there is the risk of false positives, and it's common to find nodules on CT screening. But finding nodules does not always mean cancer. In fact, studies thus far estimate that only around 5 percent of nodules found on a first lung CT screening are cancerous.

Symptoms of Lung Nodules

Most lung nodules do not have any symptoms and are found “accidentally” when a chest x-ray is done for some other reason. If symptoms are present, they may include a cough or coughing up blood if the nodule(s) is located near a major airway.

Diagnosis

The first thing your doctor will want to do if she sees a lung nodule on your x-ray is to obtain any previous x-rays you have had and compare them. If the nodule or nodules have been present for a long time, further tests may not be needed. If the nodule is new or you don’t have any prior x-rays to compare, further workup may include:

Treatment of Lung Nodules

The treatment of lung nodules varies widely depending upon the cause, whether they are related to infections, inflammation, cancer, or other conditions. Most benign lung nodules, especially those that are present and haven’t changed over a period of a few years, can be left alone.

Sources:

Cronin P. et al. Solitary Pulmonary Nodules: Meta-analytic Comparison of Cross-sectional Imaging Modalities for Diagnosis of Malignancy. Radiology. 2008. 246:772-782.

Gould M, et al. Evaluation of Patients With Pulmonary Nodules: When Is It Lung Cancer? ACCP Evidence-Based Clinical Practice Guidelines (2nd Edition). Chest. 2007. 132(no 3 suppl):108S-130S.

MacMahon H, et al. Guidelines for Management of Small Pulmonary Nodules Detected on CT Scans: A Statement from the Fleischner Society. Radiology. 2005. 237:395-400.

McWilliams M, et al. Probability of Cancer in Pulmonary Nodules Detected on First Screening CT. The New England Journal of Medicine. 2013. 39:910-919.

Wahidi M, et al. Evidence for the Treatment of Patients With Pulmonary Nodules: When Is It Lung Cancer? ACCP Evidence-Based Clinical Practice Guidelines (2nd Edition). Chest. 2007. 132(no 3 suppl):94S-107S.

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