Thousands of people congregated in the Vatican’s St. Peter’s Square on Wednesday for a Mass that Pope Leo should have been presiding over. Instead, another senior Catholic Church official took his place, while the first American pope recovered in a hospital after being diagnosed with lung cancer following an operation to remove a lobe of his right lung.

The pope’s cancer diagnosis, confirmed on Tuesday, has caused alarm across the Catholic world. Pope Leo was elected less than 18 months ago at the age of 69, the youngest man chosen to lead the Catholic Church since Pope John Paul II almost 40 years earlier. Given his relatively youthful age, the view in the Vatican and among church leaders was that Leo had a long papacy in front of him. That assumption is now being tested.

The era of papal health struggles had, many in the Vatican hoped, been put aside in the short term. Leo’s predecessor Pope Francis, elected at 76 and with part of his right lung missing, had a series of health problems towards the end of his pontificate, and spent weeks in the Gemelli hospital with pneumonia. Francis, who had served as pope since 2013, died of a stroke and heart failure in April 2025.

Pope Leo’s approach to his health has been steady, sensible and balanced. He goes to the papal retreat at Castel Gandolfo outside of Rome every Tuesday for a day off. He plays tennis, he swims, and as a cardinal had a personal trainer.

All of that added to the shock of his hospital admission. “No one expected it,” Cardinal Pietro Parolin, the Holy See Secretary of State, told reporters, likening it to a “bolt from the blue.”The cardinal, speaking before the cancer diagnosis was confirmed, added: “I am worried.”Leo XIV has cancelled all his audiences until October 20 as he continues his recovery. The doctors are confident that the cancer was removed during surgery, but further tests are needed.

For the pope, near term plans are up in the air. Leo went into hospital in the middle of a major Vatican gathering of bishops and church leaders, which he had convened. The discussions focused on how the church can support couples and families a decade on from a major document issued by Pope Francis, which opened the possibility of divorced and remarried Catholics being able to receive communion.

The meeting was an example of Leo, in his own style, seeking to implement the reforms begun by his predecessor. But his operation meant he could not take part in the Mass that concluded the gathering or take an active part in the meetings.

“It’s very concerning and I think the more recent news that it is actually a cancer is very worrying for everybody,” Archbishop Tim Costelloe, the president of the Australian Bishops’ Conference, said just off St Peter’s Square following the Mass on Wednesday. The archbishop had been taking part in the gathering and said he’d written to the pope on behalf of his country’s bishops assuring him of prayers and support.

Questions are being asked of future papal travel. From Nov. 6-17, the pope is due to be in Latin America for an intense three country tour to Uruguay, Argentina and an emotional “homecoming” to Peru, where he served as a missionary and bishop. His packed itinerary includes 14 flights, 50 events and visits to some high-altitude parts of the continent.

Archbishop Costelloe says the latest developments “inevitably” raise questions about the forthcoming trip, but stressed Leo is “a strong man, he’s a fit man” and there was plenty of hope he “can get past this.”As of Wednesday, no changes have been announced to the dates of the trip.

Leo XIV, a meticulous and details-oriented leader, made sure everything was in order before his operation. A couple of days before announcing he was going in for surgery, the pope confirmed the election of Cardinal Luis Antonio Tagle, a high-ranking Vatican official from the Philippines, to the important role of Dean of the College of Cardinals. This is the position held by the fictional Cardinal Lawrence played by Ralph Fiennes in the movie “Conclave,” released in the months before the real-life papal election that chose Leo.

The appointment of Tagle, who stood in for Leo to preside at Wednesday’s mass at the Vatican, has acquired a new significance with the pope in the hospital. The dean, who is the “first among equals” leader of the college, plays a crucial role in presiding over a conclave (providing he’s under 80) and the pre-conclave meetings. Any future papal election is considered far into the future. But the appointment of the 69-year-old Tagle, a charismatic figure previously tipped as a possible pope, was an important piece of housekeeping.

Leo’s cancer diagnosis has been met by an outpouring of public support. It offers an opportunity for him to connect with so many other individuals and families who have been affected by the illness.

“Pope Leo has shown compassionate solidarity with so many people encountering struggles and challenges in their lives,” Fr. Joseph Farrell, the leader of the Augustinian religious order and a friend of the pope, told CNN. “As Augustinians, we invite all people to show that same loving, prayerful solidarity with the Holy Father.”Leo is an Augustinian and a former leader of the order.

There is a history of cancer in the pope’s family, with his eldest brother Louis Prevost currently being treated for the illness, which he was first diagnosed with in 2017. The pope’s mother, Mildred, died of cancer in 1990. His father, also Louis, died of colon cancer and heart disease in 1997.

While inside the Vatican there is worry about his health, the cogs of the church’s central administration will keep on turning. “It’s not a case of running around pulling hair out,” one official told CNN. “We are getting on with the work inside the dicasteries (Vatican departments) which support the pope’s ministry.”And the pope can still govern the church from his hospital bed.

Those who know the pope well say he will be keen to bounce back. Elise Allen, who interviewed the pope in July 2025 for her book on Leo XIV, described the situation as a “waiting game” but it was important not to jump to too many conclusions. “He’s a very hard worker, he’s very determined, he’s going to want to get back into the swing of things very quickly if that’s possible,” she told CNN.

Allen said, however, that his hospitalization may lead him to “scale back” some of his appointments and commitments. She also pointed out that his last major health crisis, as a young missionary sent to Peru, was definitive. In 1985, soon after arriving in the country, Leo was struck down with Typhoid fever. Allen said that it was a turning point as, following his recovery, it led him to embrace his work in South America.

Both popes John Paul II and Francis show how the role of pontiff involves an element of public suffering. And as recent conclaves have elected men in their late 60s and 70s, health difficulties are never far around the corner. “Fragility deserves special attention,” Leo XIV said in his speech to the family life gathering last week. “The experience of families has something to teach everyone, since fragility belongs to our common human condition and therefore also to the life of the Church.”The pope is now embracing that same fragility and uncertainty that many others with a similar diagnosis have faced.