A solitary pulmonary nodule (SPN) is a single round or oval growth that may appear in your lungs. This type of growth is also called a solitary coin lesion. Typically, an SPN causes no symptoms. It’s usually found during a chest X-ray or CT scan.

Your doctor may perform a biopsy to find out whether the nodule is cancerous or noncancerous. About half of all SPNs are noncancerous, or benign.

These SPNs are the result of scarring, inflammation, or infections. As long as the benign nodule remains the same size, it generally won’t need to be treated.

You’re at a higher risk for developing a cancerous SPN if you smoke or have been exposed to carcinogens, or cancer-causing agents. You may also develop an SPN if you have cancer in another part of your body and it spreads (metastasizes) to your lungs.

More than half of all SPNs are noncancerous. They may have one of several causes, such as infection or scarring. Most develop as a reaction to a previous infection. When this happens, it’s called a granuloma.

Some common lung infections that can cause SPNs include:

Primary lung cancer is the most common cause of SPNs that are malignant, or cancerous. The association between lung cancer and SPN is based on multiple risk factors, including:

  • age
  • history of smoking
  • history of lung infections
  • travel history
  • work history
  • previous cancer diagnosis

It’s important to discuss all parts of your medical history with your doctor to determine whether an SPN is cancerous.

There are usually no symptoms of an SPN. Your doctor will generally discover an SPN during a chest X-ray or CT scan. These tests are usually ordered to diagnose another condition.

After your doctor discovers a nodule, they may take steps to learn whether it’s cancerous. First, your doctor will conduct a complete physical exam and take your medical history. They’ll ask whether you’re a smoker or have been exposed to agents that cause cancer.

The SPN is likely to be noncancerous if it’s less than 3 centimeters (cm) wide and has a smooth border with an even appearance. It’s also less likely to be cancerous if you’re a young nonsmoker.

In this case, your doctor may want to take a “wait and see” approach. They may order follow-up X-rays or CT scans to monitor the nodule. Your doctor may decide that a biopsy isn’t necessary if the nodule doesn’t change in 2 years.

A biopsy may be recommended if:

  • the nodule is larger than 3 cm across
  • the nodule has changed in size or appearance
  • you have other symptoms of lung cancer
  • you smoke

During a biopsy, your doctor removes a tissue sample from the SPN. They then send the sample to a laboratory for examination under a microscope. Your doctor can perform a biopsy in one of the following ways:

  • Lung needle biopsy. A needle is inserted into your lungs through your chest wall.
  • Bronchoscopy. A scope is passed through your mouth into your lungs.
  • Mediastinoscopy. A lighted instrument is inserted into the area between your lungs, called the mediastinum.

Your doctor may also order simple skin or blood tests to rule out various bacterial and fungal infections, such as tuberculosis or coccidioidomycosis.

Based on your X-ray or CT images and your physical examination, your doctor will decide whether you should have a biopsy. If not, they may recommend careful follow-up testing.

If the nodule is noncancerous and doesn’t change over the course of 2 years, you most likely won’t need any more treatment.

If a biopsy indicates that you have cancer, you should consult an oncologist, a doctor who specializes in cancer, as soon as possible. A quick diagnosis and immediate treatment can be crucial in lung cancer cases.