It often takes a chest X-ray or CT scan to spot small lung (or pulmonary) nodules, especially when a patient is asymptomatic.
At less than 3 centimeters (1.1 inches), lung nodules are less likely to press against your airway and cause any chest pain or shortness of breath or wheezing.
In the case of Pope Leo XIV, who told a gathering at the Vatican on October 11, 2026, doctors had found a nodule on his lung, it is unclear exactly how large that nodule is.
What we know so far
All we know (at time of writing on October 12, 2026) is that it was "detected at a very early stage," and that it was "well localized."
That suggests it has not spread or metastasized, although its full status is not publicly known. Doctors advised the pontiff to have his lung nodule removed.
Whether his was a chance finding — or whether the pope had presented with symptoms — we do not know.
But "incidental findings of lung nodule(s) in asymptomatic individuals" is considered an "increasingly common clinical dilemma," according to a 2019 paper published in the Annals of Thoracic Medicine.
This "dilemma" rests in part on the fact that biopsies — removing a small sample of tissue from the spot or nodule to determine whether it's malignant (cancerous) — are difficult to perform on small nodules.
The risks involved in a surgical diagnosis are considered "excessive compared to the relatively low prevalence of malignancy in the small nodules."
That's according to a 2017 paper published in the European Respiratory Review. And that may also be the dilemma that Pope Leo's doctors have faced.
Fortunately many — if not most — early-stage lung nodules are benign. It is also possible to have more than one nodule at a time, and they can all be benign.
It's said the pope will need a week to recover after his operation to remove the lung nodule. He is due to travel to Uruguay, Argentina and Peru between November 6-17.
What are lung nodules?
Lung nodules are generally defined as a white spot or lesion on the lung. They have a rounded or irregular shape.
Radiologists refer to their "opacity" because, compared to the surrounding air-filled lung tissue, lung nodules appear as white or gray spots on a CT scan — that is, they have a certain density.
Causes and symptoms of lung nodules
Lung nodules can be caused by old lung infections, foreign particles that are inhaled and get lodged in the lung, inflammation, scar tissue and indeed the onset of cancer.
At more than 3 centimeters, the nodule is defined as a mass. The bigger it gets, the greater the chance that it will obstruct your airway and the lung's ability to function.
Symptoms may start with chest pain, shortness of breath and wheezing. They may then progress to a chronic cough or coughing up of blood, fatigue, hoarseness, loss of appetite, unexplained weight loss and recurring respiratory infections like bronchitis or pneumonia.
What makes lung nodules cancerous?
It is hard to determine when lung nodules become life-threatening cancer. But one indicator of a lung nodule's malignancy is its size.
At 2 milimeters or smaller, the risk of cancer is very small and remains so up to a nodule size of about 6-7 milimeters.
The risk of cancer becomes 9%-10% at about 8 to 10 milimeters. And at larger than 1 centimeter, the risk of cancer is about 15%.
The density of a lung nodule is also a vital indicator of malignancy.
There are two main categories of lung nodule density: solid and subsolid. Subsolid nodules are further divided into pure ground-glass (nonsolid) and part-solid nodules.
According to a 2026 review article published in the New England Journal of Medicine, subsolid nodules are less prevalent than solid nodules, but they have "a higher likelihood of being malignant."
A journey through lung health
Lung nodules and lung cancer are common
It is said that radiologists see lung nodules in about 30% of chest CT scans. But that number may be rising.
A Dutch study published in 2023 cited an increase in lung nodule detections from 38% of scans in 2008 to 50% in 2019. The same study said "the proportion of patients in whom significant new nodules (≥ 5 mm) were reported increased from 9% in 2010 to 17% in 2017."
However, this may also be a result of the development of better scanning technology in recent years and the use of artificial intelligence to spot tumors.
Bearing in mind that most lung nodules are benign, lung cancer does tend to start with a lesion or nodule. And lung cancer remains the most common type of cancer and the most common cause of cancer death in the world.
The World Health Organization's International Agency for Research on Cancer says that in 2024 almost 2.65 million people were diagnosed with lung cancer and more than 1.8 million people died from the disease.
Edited by: Tim Rooks