The pope is recovering in hospital after the Vatican confirmed doctors detected cancer in his lung during surgery.
Pope Leo had a lower lobe of his right lung removed on Tuesday and was diagnosed with lung adenocarcinoma, a common form of lung cancer, the Vatican said in a medical bulletin.
Leo, 71, was admitted to Rome's Gemelli hospital on Tuesday for surgery to remove a growth on his lung that doctors found in a recent health check-up.
The pope has woken up normally and is resting in his hospital room.
Here's what to know about his diagnosis.
What is adenocarcinoma?
Adenocarcinoma is a type of cancer that starts in mucus-producing or glandular cells.
It can develop in the lungs, bowel, breast, cervix, kidney, oesophagus, pancreas, prostate and stomach.
Less commonly, it accounts for types of anal, bladder, vaginal and vulvar cancers.
Lung adenocarcinoma is often found in the outer part of the lungs.
Cancer Australia says it is the most common form of lung cancer in non-smokers and is also more likely to occur in younger people than other types of lung cancer.
What is lung cancer?
Lung cancer begins when abnormal cells grow and multiply in an uncontrolled way in the lungs.
Lung cancer can spread to the lymph nodes, pleura, brain, adrenal glands, liver and bones.
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There are two types of lung cancers: non-small cell lung cancer (NSCLC) and small cell lung cancer (SCLC), according to the Cancer Council.
NSCLCs make up about 85 per cent of lung cancers and may be classified as adenocarcinoma, squamous cell carcinoma or large cell undifferentiated carcinoma.
Squamous cell carcinoma starts in thin, flat cells and is most often found in larger airways.
Small cell lung cancers start in the middle of the lungs and usually spread faster than NSCLC.
What is the prognosis for lung adenocarcinoma?
Lung Foundation Australia says the prognosis for lung cancer is dependent on the stage, overall health of the patient and whether genetic mutations are present.
Stage 1 has a 5-year survival rate of 68 per cent.
Early detection dramatically increases the survival rate.
The Cancer Council estimates that 15,108 people were diagnosed with lung cancer in 2025 in Australia.
The average age of diagnosis is 72.
More men than women get lung cancer but rates have steadily decreased among both genders since the 1980s due to falling smoking rates.
However, the Australian Institute of Health and Welfare said that lung cancer was estimated to be the fourth most commonly diagnosed cancer in Australia.
Among the five most common cancers in Australia, its survival rates are the lowest.
Will the Pope's treatment be successful?
The pope's lead surgeon, Stefano Margaritora, and his personal physician, Luigi Carbone, said in a statement that the procedure lasted about 90 minutes and was successful, with no complications.
"In order to make the procedure curative, the lower lobe of the right lung was removed using a video-assisted technique," they said.
Human lungs have five lobes — three in the right lung and two in the left.
A medical expert told Reuters that to assess the pope's case, they would need to know the size of the tumour and whether the cancer had spread to his lymph nodes, information the Vatican did not immediately provide.
"While we have the diagnosis, we do not yet have the stage. This is critical to prognosis and treatment," said Stephen Liu, a lung cancer expert at Georgetown University in Washington and division chief of hematology-oncology at MedStar Georgetown University Hospital.
"If this is a small lung cancer with no lymph nodes involved, surgery itself is likely to be curative.
"But if final analysis reveals a greater extent of cancer involvement, this indicates a poorer prognosis."
