What is a lung nodule? Pope Leo undergoes surgery after cancer diagnosis

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This article was originally published on October 13, 2026, and is being republished by The Independent after the Pope was diagnosed with lung cancer.

Lung nodules are small growths found in the spongy tissue of the lungs. They are no more than 3 centimetres in diameter, and can be round or irregularly shaped. Anything larger is referred to as a mass.

Lung nodules are usually detected by imaging of the chest, often using an X-ray or a computed tomography (CT) scan. While some people undergo screening specifically for lung nodules due to their increased risk of cancer, many nodules are picked up incidentally from unrelated scans.

Lung nodules are very common. In a study of 10,431 non-smoking (never or former smoking) participants given a chest CT scan in the northern Netherlands, 37.7% of women and 47.5% of men had at least one lung nodule.

The Australian National Lung Screening program suggests that lung nodules will be found in up to half of all people screened, but that most are neither symptomatic nor cancer-related.

As imaging technology improves, and scans are performed more often, more lung nodules are likely to be detected.

Older people, those who smoke, people with a family history of lung cancer and those exposed to asbestos are more likely to have lung nodules.

Fortunately, most lung nodules are harmless. Around 95% of lung nodules tend to be benign (non-cancerous), and are instead caused by factors such as infections, immune-related diseases, and genetic abnormalities.

A major challenge for clinicians is deciding which nodules are likely to be harmless (or benign), and which are likely to be cancerous and require removal.

Risk assessment considers factors such as the nodule size, density and location, as well as the patient’s age, smoking status and family history of cancer.

Sarah Diepstraten is a Senior Research Officer, Blood Cells and Blood Cancer Division, WEHI (Walter and Eliza Hall Institute of Medical Research).