What Is a Lung Nodule? Is It Cancer, and How Is It Treated?

Growths in the lungs called pulmonary nodules may be of two types: benign (noncancerous) or malignant (cancerous). Lung nodules can have many causes, ranging from infections to noninfectious sarcoidosis.

Note: A tumor, also known as a neoplasm, is an abnormal mass of tissue that may be solid or fluid-filled. Not every tumor is cancer.

Tumors

• benign (noncancerous)
• premalignant (a growth that is not currently cancerous but has the potential to become cancerous in the future)
• malignant (cancerous)

What Is a Lung Nodule (Pulmonary Nodule)?

A pulmonary nodule is a small, round or oval-shaped growth in the lung. It may also be described as a “spot on the lung” or a “coin” appearance. Pulmonary nodules are smaller than 3 cm in diameter (approximately 1,2 inches). If a growth is larger than this, it is called a pulmonary mass and is more likely to represent cancer than a simple nodule.

How Common Are Lung Nodules?

Countless pulmonary nodules are discovered each year during chest X-rays or computed tomography (CT) scans. Most nodules are noncancerous (benign). A solitary (single) pulmonary nodule is found on 0.2% of all chest X-rays. Lung nodules can be found on up to half of all lung CT scans. Risk factors for a pulmonary nodule being malignant (cancerous) include a history of smoking and older age.

What Causes Lung Nodules?

There are two main types of pulmonary nodules: malignant and benign. More than 90% of pulmonary nodules smaller than two centimeters (approximately 3/4 inch) in diameter are benign.

Benign (noncancerous) pulmonary nodules can have a wide range of causes. Many result from inflammation in the lung caused by an infection that produces inflammation or illness in the body. The nodule may represent an active infection or may result from scar tissue formed after previous inflammation. Benign developmental lesions may also appear as nodules.

• Infections: Most infections associated with pulmonary nodules have a relatively mild course and are often inactive. Examples include mycobacterial infections such as Mycobacterium tuberculosis or Mycobacterium avium-intracellulare, and fungal infections such as aspergillosis, histoplasmosis, coccidioidomycosis, and cryptococcosis. Inflammation related to infections often forms what is called a granuloma . A granuloma is a small cluster of cells that forms when lung tissue becomes inflamed. Granulomas form when the immune system isolates substances it considers foreign. They are most often seen in the lungs but can also occur elsewhere in the body. Because calcium tends to accumulate in healing tissue, they may become calcified over time; this is then called a calcified nodule in the lung .
• Noninfectious causes of benign inflammatory lung nodules: Noninfectious diseases such as sarcoidosis, granulomatosis with polyangiitis (GPA), and rheumatoid arthritis also manifest as granulomas in the lungs.
• Neoplasms: Neoplasms are abnormal growths that may be benign or malignant.

Types of benign neoplasms include:

• Fibroma (a lump of fibrous connective tissue)
• Hamartoma (an abnormal grouping of normal tissues)
• Neurofibroma (a lump made of nerve tissue)
• Blastoma (a growth made of immature cells)

Types of malignant tumors include:

• Lung cancer
• Lymphoma (a growth involving lymphoid tissue)
• Carcinoid (a small, slow-growing cancerous tumor)
• Sarcoma (a tumor arising from connective tissue)
• Metastatic tumors (tumors that spread to the lungs from cancer elsewhere in the body)

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What Are the Symptoms of a Lung Nodule?

Pulmonary nodules are generally not associated with specific symptoms. If a lung nodule causes symptoms, they will be related to its underlying cause. If the nodule comes from lung cancer, the patient is often asymptomatic, but may have a new cough or hemoptysis (bloody sputum).

Most patients do not know they have a lung nodule until a chest X-ray or computed tomography (CT) scan is performed.

How Is a Lung Nodule Diagnosed?

Although most lung nodules are not malignant, identifying a nodule is very important for the early diagnosis of cancer.

Chest X-rays and CT scans: Often, the first indication of a pulmonary nodule is a spot that appears on a chest X-ray or CT scan. These tests are generally performed when a person visits a doctor with a respiratory illness.

If an X-ray or CT scan shows a lung nodule, your doctor will ask about your medical history, including whether you have had cancer before. They will want to know whether you smoke or used to smoke, and whether you have been exposed to potentially toxic or harmful environmental chemicals.

The doctor will examine the X-ray to assess the nodule’s size, shape, location, and overall appearance. Solitary pulmonary nodules visible on chest X-rays are generally at least 8 to 10 millimeters in diameter. Smaller nodules are unlikely to be visible on a chest X-ray. As a nodule becomes larger and more irregular in shape, it is more likely to be cancerous. Nodules in the upper parts of the lungs are also more likely to be cancerous.

If you have older chest X-rays, you should let your doctor examine them to determine the nodule’s growth rate. In general, malignant (cancerous) nodules approximately double in size every 6 months. Nodules with slower or faster growth rates are less likely to be cancerous.

Your doctor may recommend a CT scan to obtain a more detailed image of the nodule, or your nodule may first have been noticed on a CT scan. CT scans can provide information about specific features of the nodule, including its shape, size, location, and internal density. They are more sensitive than chest X-rays when determining the nature of a nodule. A CT scan can identify very small nodules measuring as little as 1-2 mm in diameter.

If the nodule is quite small or its characteristics suggest a very low likelihood of cancer, your doctor will probably monitor it over time with repeated chest imaging. If it does not grow over time, it is confirmed to be benign. If a concerning growth pattern is observed, further evaluation will be recommended. The interval between scans and the duration of follow-up depend on the nodule’s size and risk of malignancy.

• Positron emission tomography (PET): A PET scan can also help determine whether a nodule is malignant or benign. It uses a radioactively labeled substance, such as glucose, that is absorbed by the nodule, providing an image of its metabolic activity. Malignant cells have a faster metabolism than normal cells, consume more energy, and therefore absorb more of the radiolabeled substance. Nodules appear brighter on PET imaging when they are malignant or when active inflammation is present. PET scans must be interpreted cautiously when nodules are smaller than 8-10 mm, as they may not be clearly visible on PET imaging. For pulmonary nodules larger than 20 mm (2 cm), PET-CT is a good diagnostic tool.
• Biopsy: A biopsy is a procedure in which a small tissue sample is removed from the nodule for examination under a microscope. It may be performed when other tests are insufficient to rule out the possibility that the growth is malignant.
• Bronchoscopy: This procedure is used when it appears possible to reach the nodule through the breathing tubes. It uses a bronchoscope, a thin, light, flexible tube that can be inserted through the mouth or nose into the windpipe and the lung’s bronchus. The bronchoscope has a very small camera and biopsy instruments at its tip.
• Needle biopsy (also known as transthoracic needle biopsy): This is currently the most frequently used method for diagnosing lung nodules suspicious for cancer. The test is most successful when the nodule is near the chest wall, toward the edge of the lung. Transthoracic needle biopsy is usually performed under guidance from a CT scan called Cone Beam CT .

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How Is a Lung Nodule Treated?

If a pulmonary nodule is benign, it generally does not require treatment. If an active infection is found or an inflammatory disease is diagnosed, treatment will depend on the condition identified and the symptoms present.

If the nodule is cancerous, the cancer has not spread, and the patient is suitable, the cancer should be removed surgically.

Surgical techniques used to remove pulmonary nodules include:

• Thoracotomy: This procedure is considered open lung surgery. An incision is made in the chest wall to remove portions of diseased lung tissue. Patients generally need to remain in hospital for several days after surgery. The risk of death is low. When possible, a less invasive mini-thoracotomy may be performed.
• Video-Assisted Thoracoscopy: This procedure uses a thoracoscope, a flexible tube with a miniature camera at its tip. The thoracoscope is passed through a small incision in the chest wall. The camera allows the surgeon to view the nodule on a television screen. This technique requires a smaller incision and a shorter recovery time than a thoracotomy.

How Can Malignant Pulmonary Nodules Be Prevented?

The best way to avoid being diagnosed with a malignant lung nodule is to quit smoking if you smoke.

People without any symptoms suggesting lung cancer (asymptomatic individuals) who are aged 55-77 and have smoked for at least 30 years—even if they quit within the past 15 years—should be screened once a year with a low-dose radiation chest CT scan.

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