Inside a dark room at Bács-Kiskun County Hospital outside Budapest, Dr. Éva Ambrózay, a radiologist with more than two decades of experience, peered at a computer monitor showing a patient’s mammogram.

Two radiologists had previously said the X-ray did not show any signs that the patient had breast cancer. But Dr. Ambrózay was looking closely at several areas of the scan circled in red, which artificial intelligence software had flagged as potentially cancerous.

“This is something,” she said. She soon ordered the woman to be called back for a biopsy, which is taking place within the next week.

Advancements in A.I. are beginning to deliver breakthroughs in breast cancer screening by detecting the signs that doctors miss. So far, the technology is showing an impressive ability to spot cancer at least as well as human radiologists, according to early results and radiologists, in what is one of the most tangible signs to date of how A.I. can improve public health.

Hungary, which has a robust breast cancer screening program, is one of the largest testing grounds for the technology on real patients. At five hospitals and clinics that perform more than 35,000 screenings a year, A.I. systems were rolled out starting in 2021 and now help to check for signs of cancer that a radiologist may have overlooked. Clinics and hospitals in the United States, Britain and the European Union are also beginning to test or provide data to help develop the systems.

A.I. usage is growing as the technology has become the center of a Silicon Valley boom, with the release of chatbots like ChatGPT showing how A.I. has a remarkable ability to communicate in humanlike prose — sometimes with worrying results. Built off a similar form used by chatbots that is modeled on the human brain, the breast cancer screening technology shows other ways that A.I. is seeping into everyday life.

Widespread use of the cancer detection technology still faces many hurdles, doctors and A.I. developers said. Additional clinical trials are needed before the systems can be more widely adopted as an automated second or third reader of breast cancer screens, beyond the limited number of places now using the technology. The tool must also show it can produce accurate results on women of all ages, ethnicities and body types. And the technology must prove it can recognize more complex forms of breast cancer and cut down on false-positives that are not cancerous, radiologists said.

The A.I. tools have also prompted a debate about whether they will replace human radiologists, with makers of the technology facing regulatory scrutiny and resistance from some doctors and health institutions. For now, those fears appear overblown, with many experts saying the technology will be effective and trusted by patients only if it is used in partnership with trained doctors.

And ultimately, A.I. could be lifesaving, said Dr. László Tabár, a leading mammography educator in Europe who said he was won over by the technology after reviewing its performance in breast cancer screening.

“I’m dreaming about the day when women are going to a breast cancer center and they are asking, ‘Do you have A.I. or not?’” he said.

Hundreds of images a day

In 2016, Geoff Hinton, one of the world’s leading A.I. researchers, argued the technology would eclipse the skills of a radiologist within five years.

“I think that if you work as a radiologist, you are like Wile E. Coyote in the cartoon,” he told The New Yorker in 2017. “You’re already over the edge of the cliff, but you haven’t yet looked down. There’s no ground underneath.”

Mr. Hinton and two of his students at the University of Toronto built an image recognition system that could accurately identify common objects like flowers, dogs and cars. The technology at the heart of their system — called a neural network — is modeled on how the human brain processes information from different sources. It is what is used to identify people and animals in images posted to apps like Google Photos, and allows Siri and Alexa to recognize the words people speak. Neural networks also drove the new wave of chatbots like ChatGPT.

Many A.I. evangelists believed such technology could easily be applied to detect illness and disease, like breast cancer in a mammogram. In 2020, there were 2.3 million breast cancer diagnoses and 685,000 deaths from the disease, according to the World Health Organization.

But not everyone felt replacing radiologists would be as easy as Mr. Hinton predicted. Peter Kecskemethy, a computer scientist who co-founded Kheiron Medical Technologies, a software company that develops A.I. tools to assist radiologists detect early signs of cancer, knew the reality would be more complicated.

Mr. Kecskemethy grew up in Hungary spending time at one of Budapest’s largest hospitals. His mother was a radiologist, which gave him a firsthand look at the difficulties of finding a small malignancy within an image. Radiologists often spend hours every day in a dark room looking at hundreds of images and making life-altering decisions for patients.

“It’s so easy to miss tiny lesions,” said Dr. Edith Karpati, Mr. Kecskemethy’s mother, who is now a medical product director at Kheiron. “It’s not possible to stay focused.”

Mr. Kecskemethy, along with Kheiron’s co-founder, Tobias Rijken, an expert in machine learning, said A.I. should assist doctors. To train their A.I. systems, they collected more than five million historical mammograms of patients whose diagnoses were already known, provided by clinics in Hungary and Argentina, as well as academic institutions, such as Emory University. The company, which is in London, also pays 12 radiologists to label images using special software that teaches the A.I. to spot a cancerous growth by its shape, density, location and other factors.

From the millions of cases the system is fed, the technology creates a mathematical representation of normal mammograms and those with cancers. With the ability to look at each image in a more granular way than the human eye, it then compares that baseline to find abnormalities in each mammogram.

Last year, after a test on more than 275,000 breast cancer cases, Kheiron reported that its A.I. software matched the performance of human radiologists when acting as the second reader of mammography scans. It also cut down on radiologists’ workloads by at least 30 percent because it reduced the number of X-rays they needed to read. In other results from a Hungarian clinic last year, the technology increased the cancer detection rate by 13 percent because more malignancies were identified.

Dr. Tabár, whose techniques for reading a mammogram are commonly used by radiologists, tried the software in 2021 by retrieving several of the most challenging cases of his career in which radiologists missed the signs of a developing cancer. In every instance, the A.I. spotted it.

“I was shockingly surprised at how good it was,” Dr. Tabár said. He said that he did not have any financial connections to Kheiron and that other A.I. companies, including Lunit Insight from South Korea and Vara from Germany, have also delivered encouraging detection results.

Proof in Hungary

Kheiron’s technology was first used on patients in 2021 in a small clinic in Budapest called MaMMa Klinika. After a mammogram is completed, two radiologists review it for signs of cancer. Then the A.I. either agrees with the doctors or flags areas to check again.

Across five MaMMa Klinika sites in Hungary, 22 cases have been documented since 2021 in which the A.I. identified a cancer missed by radiologists, with about 40 more under review.

“It’s a huge breakthrough,” said Dr. András Vadászy, the director of MaMMa Klinika, who was introduced to Kheiron through Dr. Karpati, Mr. Kecskemethy’s mother. “If this process will save one or two lives, it will be worth it.”

Kheiron said the technology worked best alongside doctors, not in lieu of them. Scotland’s National Health Service will use it as an additional reader of mammography scans at six sites, and it will be in about 30 breast cancer screening sites operated by England’s National Health Service by the end of the year. Oulu University Hospital in Finland plans to use the technology as well, and a bus will travel around Oman this year to perform breast cancer screenings using A.I.

“An A.I.-plus-doctor should replace doctor alone, but an A.I. should not replace the doctor,” Mr. Kecskemethy said.

The National Cancer Institute has estimated that about 20 percent of breast cancers are missed during screening mammograms.

Constance Lehman, a professor of radiology at Harvard Medical School and chief of breast imaging and radiology at Massachusetts General Hospital, urged doctors to keep an open mind.

“We are not irrelevant,” she said, “but there are tasks that are better done with computers.”

At Bács-Kiskun County Hospital outside Budapest, Dr. Ambrózay said she had initially been skeptical of the technology — but was quickly won over. She pulled up the X-ray of a 58-year-old woman with a tiny tumor spotted by the A.I. that Dr. Ambrózay had a hard time seeing.

The A.I. saw something, she said, “that seemed to appear out of nowhere.”