Shape of Pope Leo's papacy more uncertain after cancer diagnosis

When US Cardinal Robert Prevost emerged on the balcony of St Peter's Basilica in May 2025 as Pope Leo XIV, the new leader of the Catholic Church, he struck a stark contrast with his predecessor Francis.

Leo, young for a pope at 69, appeared energetic, spoke in a strong voice and had no known history of health issues. Francis, who died at 88, had become increasingly frail during his 12-year papacy.

With the Vatican's announcement on Tuesday that Leo, now 71, had been diagnosed with lung cancer after surgeons removed part of his right lung that afternoon, the world's 1.4 billion Catholics are once again unexpectedly facing the reality of a sick pope.

Leo, the first US-born pontiff, has emerged as an increasingly influential voice beyond the Church, raising the alarm about the risks posed by artificial intelligence and drawing the ire of US President Donald Trump by criticising the Iran war.

The future shape of Leo's papacy — once expected to be dynamic, with many foreign trips and the pope taking on a leading moral role on the global stage — is now more uncertain. Medical experts say the pope's prognosis will depend on several factors, including whether the cancer has spread to his lymph nodes, which is currently unknown.

"It's too early to say how this will affect Pope Leo's agenda and his ability to carry on the duties of the papacy," John Thavis, a Vatican expert and author, told Reuters.

"If his recovery is complete and no aggressive therapy is needed, the pope may be able to carry on as usual," he said.

Planned South America trip in question

One immediate question Leo faces is whether to proceed with an 11-day tour of Uruguay, Argentina and Peru from 6 to 17 November. The trip is known to be a high priority for the pope, who spent decades as a missionary and bishop in Peru.

The original schedule, announced last month, would have made it one of the most intense foreign trips ever undertaken by a pope, with Leo leading some 50 events and giving 36 speeches across a 10-city tour.

Dr Stephen Liu, a lung cancer expert at Georgetown University in Washington and division chief of haematology-oncology at MedStar Georgetown University Hospital, said the trip might need to be postponed, depending on Leo's recovery.

"A trip to South America that quickly is possible, if this is an early-stage lung cancer and no further therapy is needed, but it is a tight timeline, and recovery is highly variable," said Liu.

Leo had been maintaining a rapid pace of foreign travel, already making four tours in 2026 and attracting large crowds. More than 800,000 people turned out to see him in Paris last month.

'One day at a time'

Catholics have often witnessed a pope dealing with illness. Francis, who had part of one lung removed as a young adult, was prone to respiratory infections. He was also hospitalised as pope for colon and hernia surgery.

John Paul II began to show symptoms of Parkinson's disease in the 1990s, although the Vatican did not confirm his diagnosis until 2003.

John XXIII died in 1963 from stomach cancer, which the Vatican did not disclose until after his death.

Benedict XVI, however, who succeeded John Paul, was the first pope to resign in 600 years, stepping down in 2013 after saying he no longer had the strength for the job.

The Vatican, long reluctant to discuss papal health issues, has been unusually transparent in Leo's case.

The pope himself announced to pilgrims in St Peter's Square on Sunday that a "localized nodule" had been found in his lung and that he needed surgery. He also said it had been detected early and was well contained.

The Vatican later provided a detailed medical bulletin hours after Leo had undergone surgery.

Another statement may be released on Wednesday afternoon, but details of the pope's prognosis are expected to take a few days as doctors carry out the necessary tests.

According to the American Cancer Society, the five-year relative survival rate for non-small-cell lung cancer is 67% when the disease remains confined to the lung.

Dr Giuseppe Cardillo, chief of thoracic surgery at Rome's San Camillo Forlanini Hospital, said removing lung cancer detected at an early stage usually resulted in an "excellent" prognosis.

Elise Allen, author of a biography of Leo for Penguin Peru, said people should not "jump the gun" in drawing conclusions about how the pope would recover.

"Let's take it one day at a time," she said.