Pope Leo was diagnosed with lung cancer after surgeons removed a part of his right lung on Tuesday, the Vatican said in a medical bulletin, marking a significant health setback for the 71-year-old pontiff.
The pope has adenocarcinoma, a common form of lung cancer, with tissue tests conducted during the operation confirming what doctors had suspected from preparatory examinations, the bulletin said.
Leo was admitted to Rome's Gemelli hospital on Tuesday for surgery to remove the growth that doctors had discovered in a recent health checkup.
The Vatican said earlier on Tuesday evening that the operation had been successful, then provided a more detailed update from the pope's lead surgeon, Dr. Stefano Margaritora, and his personal physician, Dr. Luigi Carbone.
"In order to make the procedure curative, the lower lobe of the right lung was removed using a video-assisted technique," the medical update said, making clear that the aim was to eliminate all cancerous tissue.
Human lungs have five lobes - three in the right lung and two in the left.
Medical experts said that in order to assess the pope's case, they would need to know the size of the tumor removed from him 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 Dr. 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," he told Reuters. "But if final analysis reveals a greater extent of cancer involvement, this indicates a poorer prognosis."
Resting in his hospital room
Tuesday's surgery lasted about 90 minutes and was successful with no complications, the Vatican said. The pope has woken up normally and is resting in his hospital room.
Leo left the Vatican shortly before 1 p.m. (1100 GMT) in Rome, ahead of the surgery, and was seen waving from the back of a black SUV as his convoy drove about 9 km (5.6 miles) north of the Vatican to the Gemelli.
Upon arriving at the hospital, Leo shook hands with several officials, walked in front of a waiting crowd of well-wishers, some of whom shouted 'Auguri' (best wishes), and entered through the main entrance.
The Vatican said earlier this week that the pope was expected to recover in hospital for about a week. All his public events have been canceled until October 20.
Leo, elected by the world's cardinals in May 2025, is relatively young for a Church leader. He enjoys sports, including tennis, and is not known to smoke or have had recent health issues.
The late Pope Francis, Leo's predecessor, was hospitalized several times as he grew frail in his later years. He died aged 88 in April 2025.
Leo, who spoke in a firm, clear voice at his only public event on Monday, keeps a very busy schedule. He is due to make an 11-day tour of Uruguay, Argentina and Peru from November 6 to 17, but it was unclear whether he would still go ahead.
Vatican operations continue without pope's approval during illness
The pope is the ultimate earthly authority for the world's 1.4 billion Catholics and has no deputy who steps in when he is sick.
When a pope is incapacitated, the business of the Vatican's vast bureaucracy carries on as usual, holding off on any decisions that require papal approval.
Leo, born in Chicago in 1955 as Robert Prevost, served for decades as a missionary and bishop in Peru before becoming pope. In 1985, when he was a young priest, he came down with typhoid fever in Chulucanas, Peru, and was hospitalized.
He recounted the experience in his only major interview given as pope, in a book for Penguin Peru.
Leo said the pain was so bad that he asked God to die rather than continue suffering. He took his survival as a sign from God that "We need you here (on Earth)," he said.
"I never looked back," said Leo.