What to know about pulmonary adenocarcinoma following Pope Leo's cancer diagnosis

The lower section of Pope Leo XIV's right lung was removed Tuesday by surgeons at Rome’s Gemelli hospital after the papal leader was diagnosed with pulmonary adenocarcinoma, the most common type of lung cancer.

While lung cancer is the leading cause of cancer death worldwide, experts said the disease is very treatable if caught early, as the pope’s tumor appears to have been.

Here's what to know about the pope's cancer and his prognosis.

What is pulmonary adenocarcinoma?

Lung adenocarcinoma is a common form of non-small cell lung cancer, accounting for about 40% of all lung cancer cases.

The cancer, doctors said, forms on the outer layers of the lung and typically spreads to other parts of the body more slowly than small cell lung cancer does, often allowing doctors to find tumors early.

That appears to be the case with Leo, 71, who told a crowd on Sunday that doctors had detected a growth in his lungs at "a very early stage."

"The fact that the pope got surgery first tells me that it most likely was clinical Stage 1," said Dr. David Zeltsman, director of minimally invasive thoracic surgery at Long Island Jewish Medical Center in New Hyde Park. "And now that he had an operation, we'll have to wait for the final pathology, and hopefully it will stay as pathological Stage 1."

What are the primary causes of pulmonary adenocarcinoma?

As with any lung cancer, smoking is the No. 1 risk factor for lung adenocarcinoma, according to the Lung Cancer Foundation of America. The pope is not a smoker.

However, adenocarcinoma is also the most common type of lung cancer for nonsmokers, as well as for women and people younger than 45. 

Other leading risk factors include exposure to radon gas, air pollution, asbestos and radiation, according to the American Cancer Society.

How is lung adenocarcinoma typically treated?

Surgery is often the preferred first step when an individual is diagnosed with this form of cancer.

The right lung has three sections, or lobes, while the left has two. After one lobe is removed, the rest of the lung can gradually compensate for the loss of the lobe.

"Additional therapy after surgery is dependent on the size of the tumor and whether the lymph nodes are involved," said Dr. Amna Sher, an associate professor of medicine in the hematology and oncology division at Stony Brook University Hospital. "So, generally speaking, if the tumor is large and there are lymph node involvement, in those cases we recommend adjuvant chemotherapy after surgery to decrease the chances of recurrence and improve survival."

What do we know and what do we not know about the pope's cancer and treatment?

The Vatican said surgeons removed the cancerous growth, and on Wednesday Leo underwent blood tests and a chest X-ray that confirmed his postoperative recovery was progressing normally.

"His recovery is proceeding as expected," the Vatican said in its statement Wednesday, which did not cite what stage Leo's cancer was at.

But medical experts said additional tests were needed on Leo's lymph nodes to determine if the cancer had spread and, if so, the next course of treatment.

Those options could include chemotherapy, a combination of chemotherapy and immunotherapy, or targeted therapy, experts said.

The Vatican, meanwhile, has also not released details about the size of the tumor or how many spots in the lung are involved.

Based on what we know now, what is Pope Leo's prognosis?

While the "devil will be in the details, and it's crucial to know what stage of the disease it is," Zeltsman said he suspects Leo has an excellent chance of recovery.

"All things considered, the prognosis will be OK," he said. "I think he has a very good prognosis."

While the Vatican canceled all of Leo’s audiences through Oct. 20, there was no immediate word on whether he would be able to take a planned trip to South America next month.

By Robert Brodsky

robert.brodsky@newsday.com@BrodskyRobert

Robert Brodsky is a breaking news reporter who has worked at Newsday since 2011. He is a Queens College and American University alum.